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Can fractures be predicted?

While catastrophic fractures are relatively rare - less than 2 percent of all horses racing worldwide sustain them - they account for nearly 80 percent of racing-related fatalities. Even with advances in modern veterinary medicine, fracture diagnosis can often be elusive. What if a simple blood test could reveal a fracture or a predisposition to one before it became a crisis?
Kimberly French (10 July 2008 - Issue 9)

While catastrophic fractures are relatively rare - less than 2 percent of all horses racing worldwide sustain them - they account for nearly 80 percent of racing-related fatalities. Even with advances in modern veterinary medicine, fracture diagnosis can often be elusive. What if a simple blood test could reveal a fracture or a predisposition to one before it became a crisis?

Dr. C. Wayne McIlwraith, BVSc, Ph.D., the Barbara Cox Anthony University Chair in orthopedics at Colorado State University, professor of surgery and director of the university’s Orthopedic Research Center, said, "We have been working with biomarkers for more than 10 years. If we get good biomarkers to predict a fracture, then we can draw blood samples to identify horses at risk. We are working with a company to develop a commercially viable platform for a blood test to be available within two years."

A biomarker is a substance in the blood or urine that indicates a certain disease state. In normal bone, anabolic and catabolic processes are balanced and release molecular entities as they function. Biomarkers are these molecular entities and when their levels deviate from normal, they depict a risk or progression of disease. 
There are two types of biomarkers: direct and indirect. A direct biomarker supplies a straightforward assessment of what disease process is happening while an indirect biomarker reflects inflammation, which is usually a secondary result of damage or disease.

 "We have a collection of biomarkers, which are antibody-based, that we do the testing with," McIlwraith said. "The principle is to get early degradation of the molecule and we have the antibodies to mark changes in the collagen or protein of the cartilage and bones."

In a study published in 2005 and funded by the Grayson Jockey Club Research Foundation, McIlwraith, in conjunction with fellow faculty members Dr. David Frisbie, DVM, Ph.D. and Dr. Chris Kawcak, DVM, Ph.D., studied the biomarkers of 2-and 3-year-old Southern California Thoroughbred racehorses over 10 months. They analyzed biomarkers for four types of musculoskeletal disease: bone chips, damage to the tendon and/or ligament structure, stress fractures and bucked shins.
 
From the group of 145 horses, 74 sustained an injury during the study with 60 percent incurring either bone chips or stress fractures."Not all of the markers were specific for bone but that doesn’t always mean something," Frisbie said. "It’s weird because you would think if it’s a fracture you would see the bone turnover biomarker go up, but we realized that is not always the case and as long as the marker, whatever it’s for, is related to the disease, it doesn’t really matter in the end. If you don’t have something which can predict injury in general, it’s not going to be worthwhile. What we wanted was a screening tool to say there is an impending injury and then use diagnostics like radiographs to deduce the specific injury."

The four disease processes examined are the most common in Thoroughbred racehorses and the researchers found they could predict a disease was going to occur 65 or 66 percent of the time before it did.Bone disease is "a pretty innocuous thing, but it’s like cancer," Frisbie said. "Picking it up doesn’t have to be horribly accurate because you throw a big net. If there’s a possibility, you would want to take a closer look and are happy when it’s a false alarm. As long as you do a better job, even if it only improves your percentage 10 or 15 percent, you are not letting somebody that has cancer go undetected."

Biomarkers were endorsed as useful predictors of disease in the laboratory but only one prior study was performed in a clinical setting.  A study conducted at the Royal Veterinary College in London, England, at roughly the same time as the Colorado State University project, showed significant biomarker variances in horses with bucked shins compared to horses with normal shins.

 "We wanted biomarkers to hit the pavement and work in a clinical situation," Frisbie said. "The studies in the United Kingdom were at the tracks but concentrated mainly on shin splints. We wanted to run the entire gamut of the most common Thoroughbred diseases and as far as I know, we were the first to do that." 

Racehorses are prone to fracture because they place intense pressure on their musculoskeletal system. Any location where damage from repetitive loading surpasses a horse’s innate ability to lay down new bone can become a fracture. In normal bone, cells called osteoclasts eradicate damaged or diseased bone and cells named osteoblasts replace the unsound bone with healthy tissue. When the bone cannot be restored quickly enough, open pockets develop, which make the entire bony structure susceptible to an eventual catastrophic fracture.

Dr. Susan Stover, DVM, a professor at the University of California, Davis School of Veterinary Medicine, in Davis, California, has examined numerous post-mortem fractured bones from Thoroughbred racehorses and determined that stress fractures are the precursor to catastrophic fractures.

Stover discovered a predominant fracture pattern with new bone structure on opposite surfaces in the identical site for each bone. The bone was fresh and therefore, formed shortly before the complete catastrophic fracture. Stover approximates almost 90 percent of the catastrophic fractures she has studied originated from a prior injury.
Most veterinarians believe fractures rarely occur from spontaneous events, such as a bad step or hitting the starting gate, but are the end result of insidious bone disease. 
 "I’m not saying that a misstep can’t complete the fracture propagation but the disease is already there," McIlwraith said. "All fractures start as subchondral bone disease, with subchondral bone being the bone under the cartilage. If you can identify that bone disease before the fracture then you can save the horse."

Subchondral bone’s two primary functions are to absorb stress and maintain the shape of joints.  Undue stress to this bone causes micro-damage which alerts the body to increase production to strengthen the bone. If the bone cannot remodel itself quickly enough, micro-cracks develop and could lead to bone sclerosis, an abnormal hardening of the bone, or necrosis, when cells that create bone cells die. All these forms of subchondral bone disease ultimately weaken bone structure, paving the way for catastrophic fracture and/or joint disease.Signs of disease are subtle."That’s the trouble," McIlwraith explained.

"When you have a complete fracture you can see it on radiographs but you can’t see that early bone disease. That is why we want to screen with biomarkers and go from there." 
Radiographs or x-rays illustrate pathologic change in bone and have been the main tool to diagnose fractures. While computer and digital radiography systems have improved bone definition, the bone must lose 50 percent of its density before disease can be found.

In bone scanning or nuclear scintigraphy (a subject covered in depth in Issue 8 of North American Trainer magazine), a horse is injected with radioactive technetium bonded to phosphorus and is scanned several hours later with a gamma camera for "hot spots." This technique works well by identifying early areas of inflammation and stress fractures but is very expensive and is usually used only after a horse comes up lame.

Computerized tomography (CT) diagnoses inflammation, stress fractures, early subchondral bone sclerosis and variations in subchondral bone density, but most machines require anesthesia. A portable machine is under investigation in France, but until this becomes widely available, it will remain difficult to use.
Magnetic Resonance Imaging (MRI) could prove instrumental in detecting early disease but like CT, until a portable model or standing model is developed, it’s difficult to use because it requires anesthesia.

Even though biomarkers are an exciting breakthrough, they have limitations. The liver and kidneys play a crucial role in the metabolism; therefore, the function of these organs must be considered whenever biomarkers are measured. Other factors that affect biomarker levels are exercise, age, breed, diet, sex, surgical history and general anesthesia. 
Biomarkers originate from all the bones or joints in the body, so they may not show what is happening in a specific location.

 "Biomarkers do vary," McIlwraith said. "In our study we took monthly blood samples and when a horse was injured, we looked at that horse’s biomarkers compared to a horse that was the same age and the same sex. The blood test is only a screening tool. If you find a horse at risk, then you would have to do imaging to localize it to a certain area." 
Can biomarkers discern the difference between diseased bone and bone that is remodeling to accommodate stress, but is otherwise perfectly healthy?

"In our control study, we were able to differentiate between normal exercise and pathologic change," Frisbie explained. "All the horses in the study were exercising and we were still able to deduce they were experiencing disease, so it stands to reason we could distinguish between remodeling and disease."

When the blood test is presented on the open market, its initial use will probably be relegated to trainers and owners, and not sales agencies.
 
"In a sales environment you don’t necessarily know the horse’s history," Frisbie explained. "A trainer or owner knows when a horse isn’t performing well and a blood test showing biomarkers three deviation levels above the mean would scream out to you something was wrong."
Biomarkers alone are not a cure for bone and/or joint disease, but they do hold tremendous promise to predict or prevent catastrophic injury.

Kimberly French
 (10 July 2008 - Issue 9)

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Pelvic asymmetry in racehorses - increased risk of injury?

Steeplechase racing in particular is a high risk sport for the horse. There is currently some fairly extensive research into racehorse injuries and fatalities on the racecourse, with previously published scientific reports on the subject being widely available. The racing industry is aware of the need for such reports, as the industry itself is very much in the public eye with regard to injury rates on the racecourse.

Nicole Rossa (14 February 2008 - Issue Number: 7)

By Nicole Rossa

Steeplechase racing in particular is a high risk sport for the horse. There is currently some fairly extensive research into racehorse injuries and fatalities on the racecourse, with previously published scientific reports on the subject being widely available. The racing industry is aware of the need for such reports, as the industry itself is very much in the public eye with regard to injury rates on the racecourse. 

Lameness is one of the main reasons for wastage in the racehorse industry, and was the reported cause of 68% of total horse days lost to training in a study of racehorses in England (Rossdale et al. 1985). This study also suggested that 10% of all diagnosed lameness cases were caused by tendon injury.  Overstrain injuries to the superficial digital flexor tendon (SDFT) are amongst the most common injuries observed in the athletic horse (Goodship, 1993).  It is therefore important to determine all possible causative factors of SDFT injury so that methods for preventing injury can be implemented as part of a training programme.

Hindquarter Asymmetry


The hindquarters of the horse provide the propulsion, and the forelimbs support 60% of the horse's weight.  Problems affecting the pelvic structure in the horse can lead not only to poor performance, but also to an unlevel gait and to lameness of the hindlimb.  There are to date very few scientific reports on the frequency of hindquarter asymmetries in the horse, although Bathe (2002) found that most hard working horses were likely to have some degree of pelvic asymmetry.   This factor may not always affect performance, as many successful horses have been found to have asymmetry of the pelvis.


Dalin et al. (1985) investigated the hindquarter asymmetry in Standardbred Trotters for any correlation with poor performance. He measured differences in height between the left and right tuber sacrale when the horse was standing square.  Of the 500 horses measured 39 of them showed marked hindquarter asymmetry.  In 30 horses the tuber sacrale was lower on the left, and in 9 horses it was lower on the right.  The asymmetric horses had significantly inferior performance (measured by total earnings) compared to the symmetrical horses.  All the horses were trained and raced in Sweden on a left handed track. The asymmetrical horses were also of significantly larger body size than the symmetrical horses.


In a recent study undertaken by Stubbs et al. (2006) in conjunction with the Hong Kong Jockey Club, a number of racehorses were presented for euthanasia (for injury and/or lameness).  Racing and training details were examined in detail, and a clinical examination was carried out before the horses were euthanased. Following post mortem the thoracolumbar spine and pelvis were dissected out and examined.  Although not part of the study it was noted that asymmetry of the pelvis was prevalent in many of the horses that had been dissected, the reason probably being due to a natural torsion of the pelvis as a result of training and racing on right handed tracks only.


It is suggested that asymmetrical loads on the pelvic structure caused by external factors (such as racetrack), and by internal factors (such as locomotor apparatus pain) may lead to a higher stress being placed on one hindlimb, and as a result lead to the development of pelvic asymmetry which may be apparent as pelvic rotation.  Improper movement patterns of the hindquarters, due to pain caused by overuse or from fatigue, may also result in abnormal alignment of the pelvic structure.  This in turn may then cause overloading on the forelimbs (by off loading the hindquarters) and therefore predisposing the forelimbs to injury.  If this can be proved then surely this would emphasise the importance of correcting pelvic misalignments using manipulation techniques such as chiropractic, osteopathic and myofascial release approaches.  There is some unpublished material available to support the use of McTimoney manipulation methods and other soft tissue manipulation in the correction of pelvic rotation.


Hindquarter asymmetry is often associated with sacroiliac joint lesions or with chronic hindlimb lameness.  The tuber sacrale can appear asymmetrical in clinically normal horses as well as in horses with misalignment of the sacroiliac joint (Dyson, 2004). Horses with longstanding poor performance attributed to chronic sacroiliac damage were investigated by Jeffcott et al. (1985).  The majority of these horses showed some asymmetry of the hindquarters with the tuber coxae and tuber sacrale lower on the same side that the animal was lame on. Hindquarter asymmetry may be due to some tilting or rotation of the pelvis in addition to muscle wastage of one quarter, usually the side the horse is lame on.


Abnormal Alignment 
of the Pelvis


Pelvic rotation or abnormal alignment of the pelvis to the thoracolumbar spine can be measured by the level of the tuber coxae to the ground.  If the horse is unable to produce the propulsion from its hindquarters due to discomfort in the pelvic region, then the forelimbs may be required to provide more horizontal propulsion.  The horse will in effect be pulling himself forward with his forelimbs, rather than pushing from his hindquarters.  This may result in over development of the shoulder muscles, thereby reducing the efficiency of the forelimb movement by adding unnecessary weight.


Unpublished data has suggested a positive relationship between injury to the forelimb stay apparatus and pelvic asymmetry, particularly where the presence of functional asymmetry in the hindquarters was found to be due to pelvic rotation, and not as a result of differences in individual bone lengths of the hindlimb.


Lameness and Compensatory Movement Patterns


The compensatory mechanisms of horses with lameness have been extensively researched and reported.  The potential for secondary injuries resulting from a horse's attempt to compensate for lameness by altering its gait pattern are still unclear.  Clayton (2001) found that when a lame limb is supporting body weight, the horse minimises pain by decreasing the load on that limb, resulting in a compensatory increase in the vertical forces in other limbs.  The compensating limbs are therefore subjected to abnormally high forces, and these may lead to lameness in the compensating limbs.


Uhlir et al. (1997) found that in all cases of diagnosed hindlimb lameness that true lameness of the left hind caused a compensatory lameness of the left fore, and that true stance phase lameness of the left fore caused a compensatory lameness in the right hind.


Tendon Injury
The SDFT is the most frequently injured tendon in horses. 

 In a recent study of steeplechase horses diagnosed with tendon and ligament injuries sustained during training, 89% occurred in the SDFT (Ely et al. 2005).  It has been suggested that an optimum level of exercise is required at an early age for tendon adaptation to training, but with increasing age accumulation of microdamage and localised fatigue, failure to the tendon will occur with increasing exercise (Smith et al. 1999).


The induction of injury to the SDFT occurs when loading overcomes the resistive strength of the tendon. Factors which increase the peak loading of the SDFT, such as weight of rider, ground surface, shoeing, conformation, incoordination, jumping, and speed will act not only to increase the rate of degeneration, but will also increase the risk of the onset of SDFT strain (Smith, 2006).  Therefore the prevention of tendon strain-induced injuries by reducing some of the risk factors that increase loading on the tendon may provide the most satisfactory answer.
Animal Manipulation Techniques
McTimoney Animal Manipulation aims to improve asymmetries through manipulation.  There has been much anecdotal evidence for the benefits of McTimoney Manipulation Techniques on animals (Andrews and Courtney, 1999).  There is anecdotal evidence to suggest that McTimoney and other manipulative therapies can make a difference where veterinary medication has failed (Green, 2006), although the application of manipulation techniques in veterinary medicine may be dependent of further research into the clinical effects of manipulation.


Manipulation techniques are thought to cause muscle relaxation and to correct abnormal motor patterns which may be the result of muscular imbalances and restricted joint motion or altered joint mobility (Haussler, 1999).  There is some unpublished material to support that there are significant changes in the symmetry of the pelvis after the application of McTimoney manipulation techniques, and that there is continued improvement one month after initial treatment.


Current Research into Pelvic Alignment


In a recent unpublished study a group of 40 steeplechase horses in training, all using the same gallop, were measured for pelvic asymmetry. The measurement technique used was a somewhat simple (but reliable) method.  Each horse was measured on flat, level concrete while standing completely square and weight bearing on all four limbs.  Measurements were taken vertically using a horse measuring stick with a spirit level, from the most dorsal aspect of the lateral wing on the ilium (the tuber coxae) to the ground, on the left and right sides.
Various data was collected on each horse, regarding race history, how many races run, whether "bumper" (flat races for steeplechase bred horses), hurdle or steeplechase, prize money earnings, handicap rating, and also brief veterinary history.


The aim of the study was to compare pelvic rotation in 20 sound horses to the incidence and degree of pelvic rotation in a group of 20 horses with SDFT strain in either one or both forelimbs. Both the sound horses and the injured horses were in training with the same trainer, and therefore had used the same gallops, and underwent the same training regime.


Although no significant difference was found in the number of horses with pelvic rotation in sound horses compared with the number of horses with tendon strain, there was a high incidence of pelvic rotation in the group as a whole, with a predominance towards pelvic rotation on the right. This could have been due to training methods or gallops used, and certainly warrants further research.


There was no significant association between side of pelvic rotation and side of forelimb tendon strain, but again warrants further investigation using a larger number of horses.  Due to the prevalence of right side pelvic rotation it would not have been possible to show any significant associations anyway between left and right forelimb injury.


The study did present some trends for age of horse, sex, and race history; showing that the number of horses with pelvic rotation and tendon injury increased with age.  Geldings tended towards a higher incidence of tendon injury, and mares tended towards a higher incidence of pelvic rotation. There were equal numbers of sound and injured horses for each race type, but the degree of pelvic rotation in horses that had fallen was notably larger than in the horses that had not fallen.


Future Studies into Pelvic Asymmetry


The preliminary investigation as described above has formed the basis for further research into abnormal pelvic alignment in racehorses, and whether or not there is any association between side of misalignment and side of forelimb injury.  Further research is due to be carried out with a larger sample of horses, and from different yards, to investigate whether there is any prevalence as to the side of misalignment, or if pelvic alignment is affected by training methods and the use of different gallops and that there is continued improvement one month after initial treatment.


Current Research into Pelvic Alignment


In a recent unpublished study a group of 40 steeplechase horses in training, all using the same gallop, were measured for pelvic asymmetry. The measurement technique used was a somewhat simple (but reliable) method.  Each horse was measured on flat, level concrete while standing completely square and weight bearing on all four limbs.  Measurements were taken vertically using a horse measuring stick with a spirit level, from the most dorsal aspect of the lateral wing on the ilium (the tuber coxae) to the ground, on the left and right sides. Various data was collected on each horse, regarding race history, how many races run, whether "bumper" (flat races for steeplechase bred horses), hurdle or steeplechase, prize money earnings, handicap rating, and also brief veterinary history. The aim of the study was to compare pelvic rotation in 20 sound horses to the incidence and degree of pelvic rotation in a group of 20 horses with SDFT strain in either one or both forelimbs. Both the sound horses and the injured horses were in training with the same trainer, and therefore had used the same gallops, and underwent the same training regime.
Although no significant difference was found in the number of horses with pelvic rotation in sound horses compared with the number of horses with tendon strain, there was a high incidence of pelvic rotation in the group as a whole, with a predominance towards pelvic rotation on the right. This could have been due to training methods or gallops used, and certainly warrants further research.


There was no significant association between side of pelvic rotation and side of forelimb tendon strain, but again warrants further investigation using a larger number of horses.  Due to the prevalence of right side pelvic rotation it would not have been possible to show any significant associations anyway between left and right forelimb injury.


The study did present some trends for age of horse, sex, and race history; showing that the number of horses with pelvic rotation and tendon injury increased with age.  Geldings tended towards a higher incidence of tendon injury, and mares tended towards a higher incidence of pelvic rotation. There were equal numbers of sound and injured horses for each race type, but the degree of pelvic rotation in horses that had fallen was notably larger than in the horses that had not fallen.

 

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Strengthening Young Thoroughbreds' Limbs

One of the major challenges in training racehorses is keeping them sound. Not unlike a human athlete, a racehorse's ligaments, tendons, bones and joints are susceptible to injury throughout its career and, at times, it seems impossible to avoid some sort of musculoskeletal mishap.
Kimberly French (14 February 2008 - Issue 7)

One of the major challenges in training racehorses is keeping them sound. Not unlike a human athlete, a racehorse's ligaments, tendons, bones and joints are susceptible to injury throughout its career and, at times, it seems impossible to avoid some sort of musculoskeletal mishap.

A vast number of components can comprise any musculoskeletal injury but many believe the economics of the Thoroughbred industry - namely the preparation of young horses for 2-year-old sales and racing 2-year-olds - are the main culprits for these sorts of injuries.
Training for most race horses commences when they are 18 to 20 months old. The skeleton of a horse often does not reach full maturity until they are four years old so training at a young age might predispose horses to a multitude of career-limiting or -ending injuries.
Shin soreness or bucked shins is an extremely common condition in young racing Thoroughbreds and Quarter Horses (and occasionally Standardbreds.) It involves the front portion of the cannon or metacarpal bone and is the result of rapid bone modeling.
Before a horse begins training, its cannon bones have the same thickness all the way around. When horses start galloping, there is a considerable increase in stress on the front of the cannon bone.  To contend with the stress, the equine body responds by adding new bone to the area in duress. Ultimately, this creates stronger bones but early on this new bone is prone to microfractures similar to the stress fractures that human athletes endure during training.
The severity of bucked shins can vary greatly, but most horses will exhibit pain when the cannon bone area is massaged, will be lame while trotting, and have a short, choppy stride. Another symptom is swelling in this area of the leg.
The condition is usually diagnosed by recognizing the clinical indicators in a horse when it begins its first training and/or racing campaign. Horses suffering from shin soreness must be rested until all signs of lameness have disappeared, which can take several days or many months.
For example, New York-based trainer Barclay Tagg's then 2-year-old colt, Tale of Ekati, had sore shins and returned after a month of light training to triumph in the Grade 2, $250,000 Belmont Futurity on September 15th of last year.
"One shin was very sore, but he got over it very quickly," Tagg said. "I got two real good works into him."
While Maimonides, a 2-year-old, owned by Ahmed Zayat, exited the Grade 1 Hopeful Stakes held at Saratoga Race Course on September 3 with the same affliction, his recovery was expected to take a bit longer. Sonny Sonbol, Zayat's racing manager, said he needed "three to four weeks to get over his shins and start back training and get ready for the winter."
Estimates vary, but it is believed between 65 and 90 percent of all Thoroughbreds in the United States and more than 40 percent of all Thoroughbreds in Australia buck their shins early in training.
About only 12 percent of young English racehorses buck their shins. Unlike the United States and Australia, much less emphasis is placed on 2-year-old racing in England and English horses are trained on straight tracks, so less strain would be placed on the cannon bone.
However, the English are not immune to their young horses being injured. In a study of 314 young Thoroughbreds in Newmarket more than 50 percent experienced some period of lameness, and in roughly 20 percent of those horses, the lameness prevented them from racing.
Also, bucked shins are not exclusively relegated to 2-year-olds but to all horses which are just beginning intense training. Some horses can suffer recurrences of shin soreness after a period of stall of paddock rest. Therefore, bucked shins do not discriminate based on the age of a horse, but depend on how intense the training is and if the horse is undertaking the action for the first time.
Dr. David Nunamaker, VMD, PhD, is an orthopedic surgeon and chair of the research department at the University of Pennsylvania's New Bolton Center who had conducted extensive research on bone development from 1982 to the present. Dr. Nunamaker, Dr. William Moyer, DVM, chair of the Large Animal and Surgery Department at Texas A&M University and Dr. John Fisher, DVM, an equine veterinarian and Maryland horse trainer, analyzed their research results and established a training system created to reduce the severity of bucked shins or erase them.
"We found that a horse's bone shape alters in response to its training," Dr. Nunamaker said. "The way most conventional training is conducted, a bone changes in a way it should not and that is why you get into trouble with bucked shins. Also saucer fractures seem to occur only in horses that have previously bucked their shins. This could lead to catastrophic fracture."
Dr. Nunamaker concluded a problem will become evident after 50,000 cycles of trotting and galloping. A cycle is equal to one swift stride.
"The Standardbred doesn't have issues with bucked shins because you never see a pacer do anything but pace while Thoroughbreds train with a variety of gaits, such as walking, trotting and galloping," Dr. Nunamaker said. "Thoroughbreds do not run while they are training and when they do run it's only every 10 to 14 days. The bone remodels to what it experiences - which is not racing."
Speed work is very important because when a horse runs at speed, the angle of strain is much greater. So horses that breeze more often remodel their bones for racing.
Utilizing the research results, Dr. John Fisher adheres to a training program that stresses and stimulates the cannon gradually.
"When a horse is breezed, the bone sees it as an emergency and immediately begins laying down new bone," Dr. Fisher said. "This new bone is weak and needs to be strengthened through later remodeling, which would be triggered by further breezes spaced closer together. If remodeling is not allowed to take place and the horse is asked to do too much before he is ready, the new bone will be weak and prone to injury. The bone-strengthening is entirely based on stress and recovery to gradually increase bone density and strength."
In Dr. Fisher's program, horses transition from a one furlong work at 15 seconds to a half-mile or more in 13 seconds over a 16-week period.
If there are more than four days between short distance works, Drs. Nunamaker and Fisher have discovered the new bone will stop rebuilding and actually weaken, with no additional stress after five days.
Once the program has been finished, a horse is prepared to begin conventional training because he should have accumulated enough bone strength that he will not buck shins. However, if a horse is subjected to different track conditions or circumferences, such as a European horse racing on American dirt, the threat of shin soreness resurfaces.
Even though Dr. Fisher has modified the program throughout the years, he is still quite pleased with its performance.
"We just don't have many injuries at all," Dr Fisher said. "No more tendons, no more suspensories, no more fractures."
How much high-speed work and distance are required to signal the bone to remodel itself correctly and not form weaker bone? Research is still being conducted but Dr. Nunamaker claims the goal is to correctly change the bone at the slowest possible speed over the shortest possible distance.
 
"Maybe two furlongs, maybe one furlong," Dr. Nunamaker said. "Maybe it won't even have to be that far. We just don't know but there is a fine line during a crucial time period as to what is too much and what is not enough."
Once the bone has attained maximum strength by becoming thicker at its stress points, it should stay that way.
"When we looked at the timing of the injuries that occurred in horses that have shin injuries, we found that when the horse reached four years old, it no longer had shin injuries," Dr. Nunamaker said. "It may develop injuries to other parts of its body, but not to the shins. It is in the first two years of its training program, if it starts at two years of age, that it is going to have shin injury problems. After that no more shin injuries."
It is important to note the bones are the slowest part of the body to train. In most cases, the cardiovascular system and soft tissues are prepared for the stress of racing before the bones.
Study results presented at the 2005 Australian Veterinary Association depict shin soreness or bucked shins can be avoided. Certain training techniques place horses at risk for this condition.
The most significant factor was how far the horse trained and how quickly he went. If a horse trained at a speed greater than 33 mph during its first ten weeks of training, he tended to have some shin pain.
"A gradual increase in the weekly distances at these speeds is the key to reducing the number of cases," Dr. David Evans, BVSc, PhD and associate professor of veterinary science at the University of Sydney and one of the researchers on the project, said.
The study also revealed that using short gallops of 200-300 meters at 33 mph or greater can decrease shin soreness; training horses to induce shin soreness will not reduce the risk of contracting the condition during subsequent training; and shin pain occurred much less often in horses that began training at an average age of 30 months.
Dr. Evans acknowledged that much more research was necessary before any authoritative program could be implemented.
K.L.P. Verheyen, DVM, MSc, PhD, MRCVS, of the Royal Veterinary College (RVC) in London, agrees with Drs. Nunamaker and Evans that training methods are associated with injury risk.
"Stress injuries are repetitive loading injuries," Dr. Verheyen said. "Compare it to a paper clip and if you keep bending it, it will break. Interval training (alternate periods of hard exertion and rest) is a better option because high-speed exercise is as not bad as previously thought. It actually stimulates bone to respond, because bone is a living tissue and is constantly remodeling. If the same exercise is repeated again and again, the bone will stop responding, which is what we think is happening with the low-speed exercise and stress fractures."
While more research must be conducted to provide greater insight into how equine bones adapt and grow, even less is known about how tendons and ligaments respond to training. In a series of recent studies, Allan Goodrich, a professor at the Royal Veterinary College and the University College of London, discovered that the tendons of young horses (less than two years) strengthen in response to training. These results raise the possibility that early training enhances the development of the limb's support structures and could diminish injuries during training and racing.
After reviewing training methods and treatments, it is obvious much more research must be completed before any sound strength management program can be introduced.
"We just don't have all the answers yet," Dr. Nunamaker said.

Kimberly French 
(14 February 2008 - Issue 7)

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Current research on Pelvic Asymmetry in Racehorses

Steeplechase racing in particular is a high risk sport for the horse. There is currently some fairly extensive research into racehorse injuries and fatalities on the racecourse, with previously published scientific reports on the subject being widely available.

Nicole Rossa (European Trainer - issue 19 - Autumn 2007)

Steeplechase racing in particular is a high risk sport for the horse. There is currently some fairly extensive research into racehorse injuries and fatalities on the racecourse, with previously published scientific reports on the subject being widely available. The racing industry is aware of the need for such reports, as the industry itself is very much in the public eye with regard to injury rates on the racecourse. Lameness is one of the main reasons for wastage in the racehorse industry, and was the reported cause of 68% of total horse days lost to training in a study of racehorses in England (Rossdale et al. 1985).

This study also suggested that 10% of all diagnosed lameness cases were caused by tendon injury. Overstrain injuries to the superficial digital flexor tendon (SDFT) are amongst the most common injuries observed in the athletic horse (Goodship, 1993). It is therefore important to determine all possible causative factors of SDFT injury so that methods for preventing injury can be implemented as part of a training programme.

HINDQUARTER ASYMMETRY

The hindquarters of the horse provide the propulsion, and the forelimbs support 60% of the horse’s weight. Problems affecting the pelvic structure in the horse can lead not only to poor performance, but also to an unlevel gait and to lameness of the hindlimb. There are to date very few scientific reports on the frequency of hindquarter asymmetries in the horse, although Bathe (2002) found that most hard working horses were likely to have some degree of pelvic asymmetry.

This factor may not always affect performance, as many successful horses have been found to have asymmetry of the pelvis. Dalin et al. (1985) investigated the hindquarter asymmetry in Standardbred Trotters for any correlation with poor performance. He measured differences in height between the left and right tuber sacrale when the horse was standing square. Of the 500 horses measured 39 of them showed marked hindquarter asymmetry. In 30 horses the tuber sacrale was lower on the left, and in 9 horses it was lower on the right. The asymmetric horses had significantly inferior performance (measured by total earnings) compared to the symmetrical horses.

All the horses were trained and raced in Sweden on a left handed track. The asymmetrical horses were also of significantly larger body size than the symmetrical horses. In a recent study undertaken by Stubbs et al. (2006) in conjunction with the Hong Kong Jockey Club, a number of racehorses were presented for euthanasia (for injury and/or lameness). Racing and training details were examined in detail, and a clinical examination was carried out before the horses were euthanased. Following post mortem the thoracolumbar spine and pelvis were dissected out and examined. Although not part of the study it was noted that asymmetry of the pelvis was prevalent in many of the horses that had been dissected, the reason probably being due to a natural torsion of the pelvis as a result of training and racing on right handed tracks only.

It is suggested that asymmetrical loads on the pelvic structure caused by external factors (such as racetrack), and by internal factors (such as locomotor apparatus pain) may lead to a higher stress being placed on one hindlimb, and as a result lead to the development of pelvic asymmetry which may be apparent as pelvic rotation. Improper movement patterns of the hindquarters, due to pain caused by overuse or from fatigue, may also result in abnormal alignment of the pelvic structure.

This in turn may then cause overloading on the forelimbs (by off loading the hindquarters) and therefore predisposing the forelimbs to injury. If this can be proved then surely this would emphasise the importance of correcting pelvic misalignments using manipulation techniques such as chiropractic, osteopathic and myofascial release approaches. There is some unpublished material available to support the use of McTimoney manipulation methods and other soft tissue manipulation in the correction of pelvic rotation. Hindquarter asymmetry is often associated with sacroiliac joint lesions or with chronic hindlimb lameness.

The tuber sacrale can appear asymmetrical in clinically normal horses as well as in horses with misalignment of the sacroiliac joint (Dyson, 2004). Horses with longstanding poor performance attributed to chronic sacroiliac damage were investigated by Jeffcott et al. (1985). The majority of these horses showed some asymmetry of the hindquarters with the tuber coxae and tuber sacrale lower on the same side that the animal was lame on. Hindquarter asymmetry may be due to some tilting or rotation of the pelvis in addition to muscle wastage of one quarter, usually the side the horse is lame on.

ABNORMAL ALIGNMENT OF THE PELVIS

Pelvic rotation or abnormal alignment of the pelvis to the thoracolumbar spine can be measured by the level of the tuber coxae to the ground. If the horse is unable to produce the propulsion from its hindquarters due to discomfort in the pelvic region, then the forelimbs may be required to provide more horizontal propulsion. The horse will in effect be pulling himself forward with his forelimbs, rather than pushing from his hindquarters. This may result in over development of the shoulder muscles, thereby reducing the efficiency of the forelimb movement by adding unnecessary weight. Unpublished data has suggested a positive relationship between injury to the forelimb stay apparatus and pelvic asymmetry, particularly where the presence of functional asymmetry in the hindquarters was found to be due to pelvic rotation, and not as a result of differences in individual bone lengths of the hindlimb.

LAMENESS AND COMPENSATORY MOVEMENT PATTERNS

The compensatory mechanisms of horses with lameness have been extensively researched and reported. The potential for secondary injuries resulting from a horse’s attempt to compensate for lameness by altering its gait pattern are still unclear. Clayton (2001) found that when a lame limb is supporting body weight, the horse minimises pain by decreasing the load on that limb, resulting in a compensatory increase in the vertical forces in other limbs. The compensating limbs are therefore subjected to abnormally high forces, and these may lead to lameness in the compensating limbs. Uhlir et al. (1997) found that in all cases of diagnosed hindlimb lameness that true lameness of the left hind caused a compensatory lameness of the left fore, and that true stance phase lameness of the left fore caused a compensatory lameness in the right hind. TENDON INJURY The SDFT is the most frequently injured tendon in horses. In a recent study of steeplechase horses diagnosed with tendon and ligament injuries sustained during training, 89% occurred in the SDFT (Ely et al. 2005). It has been suggested that an optimum level of exercise is required at an early age for tendon adaptation to training, but with increasing age accumulation of microdamage and localised fatigue, failure to the tendon will occur with increasing exercise (Smith et al. 1999). The induction of injury to the SDFT occurs when loading overcomes the resistive strength of the tendon. Factors which increase the peak loading of the SDFT, such as weight of rider, ground surface, shoeing, conformation, incoordination, jumping, and speed will act not only to increase the rate of degeneration, but will also increase the risk of the onset of SDFT strain (Smith, 2006). Therefore the prevention of tendon strain-induced injuries by reducing some of the risk factors that increase loading on the tendon may provide the most satisfactory answer.

ANIMAL MANIPULATION TECHNIQUES

McTimoney Animal Manipulation aims to improve asymmetries through manipulation. There has been much anecdotal evidence for the benefits of McTimoney Manipulation Techniques on animals (Andrews and Courtney, 1999). There is anecdotal evidence to suggest that McTimoney and other manipulative therapies can make a difference where veterinary medication has failed (Green, 2006), although the application of manipulation techniques in veterinary medicine may be dependent of further research into the clinical effects of manipulation. Manipulation techniques are thought to cause muscle relaxation and to correct abnormal motor patterns which may be the result of muscular imbalances and restricted joint motion or altered joint mobility (Haussler, 1999). There is some unpublished material to support that there are significant changes in the symmetry of the pelvis after the application of McTimoney manipulation techniques, and that there is continued improvement one month after initial treatment.

CURRENT RESEARCH INTO PELVIC ALIGNMENT

In a recent unpublished study a group of 40 steeplechase horses in training, all using the same gallop, were measured for pelvic asymmetry. The measurement technique used was a somewhat simple (but reliable) method. Each horse was measured on flat, level concrete while standing completely square and weight bearing on all four limbs. Measurements were taken vertically using a horse measuring stick with a spirit level, from the most dorsal aspect of the lateral wing on the ilium (the tuber coxae) to the ground, on the left and right sides. Various data was collected on each horse, regarding race history, how many races run, whether “bumper” (flat races for steeplechase bred horses), hurdle or steeplechase, prize money earnings, handicap rating, and also brief veterinary history. The aim of the study was to compare pelvic rotation in 20 sound horses to the incidence and degree of pelvic rotation in a group of 20 horses with SDFT strain in either one or both forelimbs. Both the sound horses and the injured horses were in training with the same trainer, and therefore had used the same gallops, and underwent the same training regime. Although no significant difference was found in the number of horses with pelvic rotation in sound horses compared with the number of horses with tendon strain, there was a high incidence of pelvic rotation in the group as a whole, with a predominance towards pelvic rotation on the right.

This could have been due to training methods or gallops used, and certainly warrants further research. There was no significant association between side of pelvic rotation and side of forelimb tendon strain, but again warrants further investigation using a larger number of horses. Due to the prevalence of right side pelvic rotation it would not have been possible to show any significant associations anyway between left and right forelimb injury. The study did present some trends for age of horse, sex, and race history; showing that the number of horses with pelvic rotation and tendon injury increased with age. Geldings tended towards a higher incidence of tendon injury, and mares tended towards a higher incidence of pelvic rotation. There were equal numbers of sound and injured horses for each race type, but the degree of pelvic rotation in horses that had fallen was notably larger than in the horses that had not fallen.

FUTURE STUDIES INTO PELVIC ASYMMETRY

The preliminary investigation as described above has formed the basis for further research into abnormal pelvic alignment in racehorses, and whether or not there is any association between side of misalignment and side of forelimb injury. Further research is due to be carried out with a larger sample of horses, and from different yards, to investigate whether there is any prevalence as to the side of misalignment, or if pelvic alignment is affected by training methods and the use of different gallops.

 

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Nutritional Support for bone - maintaining a strong skeleton

The expression ‘no foot no horse’ should perhaps be extended to cover all the bones of the skeleton, for as far as racehorses are concerned, without strength and durability in this area a trainer’s job is fraught with difficulties.

Dr Catherine Dunnett (European Trainer - issue 16 - Winter 2006)

The expression ‘no foot no horse’ should perhaps be extended to cover all the bones of the skeleton, for as far as racehorses are concerned, without strength and durability in this area a trainer’s job is fraught with difficulties. The number of training days lost to lameness in a season is testament to this. A racehorse’s diet should help to maintain the skeletal system during rigorous training. This task is no doubt easier when the skeletal foundations have been firmly laid in utero and during the rapid growing phase.

The formation of cartilage and its subsequent conversion to bone ‘proper’ is one of the key processes to highlight. Long bones develop in the foetus from early bone templates that are composed entirely of cartilage. Conversion of cartilage to bone occurs initially within a central area of ossification (bone formation) within the long bones, known as the diaphysis and then also at each end of the bone (epiphysis). There are various abnormalities that can occur during the development of bones and joints that may involve problems during the localised conversion of cartilage to bone, or with bone lengthening, or changes within the bone after it has formed, once a horse has commenced training. Nutrition is only one of many factors involved in DOD Osteochondrosis (OCD) involves disruption to the normal conversion of cartilage to bone within the areas of ossification. For many years, researchers viewed nutrition as the key to OCD, however, it is now recognised that genetic predisposition, body size and mechanical stress, as well as trauma are all additional factors that must be considered.

Whilst diets that simply oversupply energy have been demonstrated to increase the incidence of OCD, the previously hypothesised causal link with excessive protein intake has not been proven. This suggests that the source of the energy in feed is an important issue. Recent research supports this, as it has been reported that diets with a high glycemic nature, i.e. those with a high starch and sugar content (typical of the more traditional stud and youngstock rations), appear to be more likely to trigger OCD. However, one would suspect that this would be more apparent in genetically susceptible animals. Many mineral imbalances in the diet have also been implicated as causative factors in OCD, but few have any strong evidence to support their role. For example, OCD lesions have been reproduced experimentally in foals maintained on a very high phosphorus intake.

This type of diet could arise inadvertently by feeding straight cereals such as oats, without a suitable balancer or complementary feed such as alfalfa to redress the low calcium to phosphorus ratio in the grain. Less extreme versions of this diet could occur through excessive top dressing of ‘balanced’ coarse mix or cubes with additional cereals such as oats or barley, as is common practice in many yards. A low copper intake, especially during the last trimester of pregnancy, has also been implicated in OCD. Copper has received particular focus due to its functional role in the activity of a key enzyme involved in formation of the collagen cross-links. However, other trace minerals including manganese and zinc may be equally important during this key stage in a foal’s development in utero, as they are necessary co-factors for important enzymes involved in regulating cartilage metabolism. Blood tests that challenge the premise that horses are unaffected by molybdenum levels in grazing In grazing youngsters, a secondary copper deficiency can be caused by excessive molybdenum levels in pasture. In cattle, bacteria in the rumen form complexes between molybdenum and sulphur.

These thiomolybdate complexes will bind copper within the gut and when absorbed will then search out further copper to bind, either circulating in the blood or in association with copper dependent enzymes. This can severely impair the activity of some key enzymes involved in growth processes and cartilage turnover. However, as a horses gut is somewhat different from a cow’s, in that the hindgut (the equivalent of the rumen) is positioned after the small intestine and not before, there is theoretically less opportunity for these thiomolybdates to be absorbed and ‘cause trouble’. At least this is what has been largely accepted from previous studies in horses that focussed on plasma copper levels and copper absorption. However, new blood tests that can be used to measure the activities of key copper dependent enzymes, such as superoxide dismutase (SOD), in conjunction with traditional measurements of plasma copper status and the presence of thiomolybdate complexes suggest that this may not always be the case.

Dr Stewart Telfer of Telsol Ltd, routinely carries out such tests in cattle and has to date analysed about 100 samples in horses suspected of having an issue with molybdenum interactions. He says, “From our work, it is clear that horses do suffer from molybdenum (thiomolybdate) toxicity. The interactions between copper, iron, molybdenum and sulphur will take place in the horse’s gut and in certain situations, not always linked to a high molybdenum intake, will result in the horse suffering from molybdenum (thiomolybdate) toxicity. Dr Telfer however, acknowledges that only relatively small numbers of samples in horses have been tested and the laboratory does not currently have a definitive reference range for horses. Calcium and phosphorus may be mobilized from bone to compensate for ‘acidic diets’ When yearlings first move into training yards, they usually experience a significant change in their diet that has consequences for bone metabolism during this period in their lives when some continued growth occurs and the skeletal system is put under considerable strain. In general terms, a ‘stud diet’ has what’s called a high dietary anion to cation ratio (DCAB).

This is largely due to the high inclusion of ingredients like soya and forages. A ‘full race training diet’ on the other hand tends to have a much lower DCAB (is more acidic) due to the reduction in forage intake and higher inclusion of cereals such as oats. The significance of a low DCAB is that it reduces the efficiency of calcium absorption and retention within the body and may contribute to the reduction in bone density seen in horses in early training. This surely is an argument for limiting the intake of cereals and maximising forage intake during the early stages of training when a high cereal intake is largely unnecessary. Calcium is the most abundant mineral in the horse's body, with the majority being present in the skeletal system. Phosphorus is also found in large amounts in bone in close association with calcium.

A racehorse’s diet should provide an adequate intake of both minerals but also needs to provide a balanced calcium to phosphorus ratio of near to 2:1. Although exercise demands a slight increase in calcium intake above the requirements for maintenance, this is usually satisfied by the generalised increase in feed intake. However, the efficiency with which individual horses absorb calcium varies and should certainly be investigated when a calcium-related issue arises. This can be achieved by examining an individual horse’s calcium and phosphorus status, by looking at the diet and also within the body using a creatinine clearance test. Topdressing – a national pastime When using straight feeds, or when topdressing ‘straights’ onto a ‘balanced’ racing mix or cubes, be aware that certain types of feed are much higher in calcium relative to phosphorus and vice versa (see table). Alfalfa, with its high calcium to phosphorus ratio, makes an ideal partner for cereals, which are low in calcium relative to phosphorus. Conversely, the traditional combination of oats and bran is not ideal, as it combines two feeds, which are low in calcium.

Remember that you can use a supplement or feed balancer to carefully correct any deficiencies or imbalances when feeding straights. Equally excessive addition of oats to a balanced mix or cube can decrease the calcium to phosphorus ratio sufficiently to cause problems. Most commercial mixes or cubes have sufficiently high calcium to phosphorus ratios to practically be able to withstand the addition of 1-2kg of oats daily, however any increase beyond this is unwise without further corrective measures. Feeds High in Calcium &Low in Phosphorus Feeds Low in Calcium & High Phosphorus Alfalfa Oats Sugar Beet Barley Seaweed Maize Wheat Bran Horses have a complex regulatory system, involving certain hormones, for ensuring that the proportion of calcium in the body, relative to that of phosphorus, remains stable and that the level of active or ‘ionised’ calcium in the blood remains within tight limits. If for one reason or another the level of calcium relative to phosphorus in the blood drops, a number of safety systems will be triggered to redress the balance. Bone acts as a reservoir of both calcium and phosphorus, which can be drawn on when necessary. The body's balance of calcium and phosphorus is continually 'corrected' by either conservation or loss of calcium or phosphorus in the urine, via the kidneys or through the skeletal system. Sustained calcium and phosphorus imbalance can, however, contribute to developmental orthopaedic diseases (DOD) in young horses, or lameness and sometimes bone fractures in mature horses. Research shows silicon is a trace mineral worth a second look.

Moving on to a less well-recognised trace mineral as far as bone is concerned, there has been some interesting research carried out into the effects of supplemental silicon in the racehorse’s diet. Silicon is a natural constituent of plants and provides structure and rigidity to some of their cell walls. It therefore forms a natural part of the horse’s diet, however, the availability in horse feed is apparently limited. Silicon plays a role in the development of new bone and is also important for the calcification process. It is therefore a relevant micronutrient for horses in training, as bone is dynamic and is constantly undergoing change, in response to forces placed upon it during the training process.

Research carried out by Dr Brian Nielsen at Michigan State University in the early nineties reported a dramatic decrease in injury rates in quarter horses fed a bioavaiable form of silicon as sodium zeolite A. This program of research has also established that the silicon is available to foals via the milk of supplemented mares. However, thus far the group have not uncovered the mechanism by which the beneficial effects of silicon are brought about. However, the form in which sodium zeolite A is fed (a chalk like powder) and the level of intake used in these studies (about 200g per day for a 500kg horse) makes it impractical to use as a feed supplement unless it can be incorporated within a feed pellet. In conclusion, attention to those factors within the diet that support bone turnover is likely to contribute to a reduction in injuries observed, however, the implementation of appropriate training techniques and use of suitable training surfaces also has a huge impact on the durability of horses in training in comparative terms.

 

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Bones of contention - how to maintain a strong skeleton

The expression no foot no horse’ should perhaps be extended to cover all the bones of the skeleton, for as far as racehorses are concerned, without strength and durability in this area a trainer’s job is fraught with difficulties. The number of training days lost to lameness in a season is testament to this. A racehorse diet should help to maintain the skeletal system during rigorous training. This task is no doubt easier when the skeletal foundations have been firmly laid in utero and during the rapid growing phase.

Dr Catherine Dunnet (19 October 2006 - Issue Number: 2)

By Catherine Dunnett

The expression ‘no foot no horse’ should perhaps be extended to cover all the bones of the skeleton, for as far as racehorses are concerned, without strength and durability in this area a trainer’s job is fraught with difficulties.  The number of training days lost to lameness in a season is testament to this.   A racehorse’s diet should help to maintain the skeletal system during rigorous training.  This task is no doubt easier when the skeletal foundations have been firmly laid in utero and during the rapid growing phase.

The formation of cartilage and its subsequent conversion to bone ‘proper’ is one of the key processes to highlight.  Long bones develop in the foetus from early bone templates that are composed entirely of cartilage.  Conversion of cartilage to bone occurs initially within a central area of ossification (bone formation) within the long bones, known as the diaphysis and then also at each end of the bone (epiphysis). 

There are various abnormalities that can occur during the development of bones and joints that may involve problems during the localised conversion of cartilage to bone, or with bone lengthening, or changes within the bone after it has formed, once a horse has commenced training.

Nutrition is only one of many factors involved in DOD
Osteochondrosis (OCD) involves disruption to the normal conversion of cartilage to bone within the areas of ossification.  For many years, researchers viewed nutrition as the key to OCD, however, it is now recognised that genetic predisposition, body size and mechanical stress, as well as trauma are all additional factors that must be considered.  Whilst diets that simply oversupply energy have been demonstrated to increase the incidence of OCD, the previously hypothesised causal link with excessive protein intake has not been proven. 

This suggests that the source of the energy in feed is an important issue.  Recent research supports this, as it has been reported that diets with a high glycemic nature, i.e. those with a high starch and sugar content (typical of the more traditional stud and youngstock rations), appear to be more likely to trigger OCD. 

However, one would suspect that this would be more apparent in genetically susceptible animals.

Many mineral imbalances in the diet have also been implicated as causative factors in OCD, but few have any strong evidence to support their role.  For example, OCD lesions have been reproduced experimentally in foals maintained on a very high phosphorus intake.  This type of diet could arise inadvertently by feeding straight cereals such as oats, without a suitable balancer or complementary feed such as alfalfa to redress the  low calcium to phosphorus ratio in the grain.  Less extreme versions of this diet could occur through excessive top dressing of ‘balanced’ coarse mix or cubes with additional cereals such as oats or barley, as is common practice in many yards. 

A low copper intake, especially during the last trimester of pregnancy, has also been implicated in OCD.  Copper has received particular focus due to its functional role in the activity of a key enzyme involved in formation of the collagen cross-links.  However, other trace minerals including manganese and zinc may be equally important during this key stage in a foal’s development in utero, as they are necessary co-factors for important enzymes involved in regulating cartilage metabolism. 


Blood tests that challenge the premise that horses are unaffected by molybdenum levels in grazing

In grazing youngsters, a secondary copper deficiency can be caused by excessive molybdenum levels in pasture.  In cattle, bacteria in the rumen form complexes between molybdenum and sulphur.  These thiomolybdate complexes will bind copper within the gut and when absorbed will then search out further copper to bind, either circulating in the blood or in association with copper dependent enzymes.  This can severely impair the activity of some key enzymes involved in growth processes and cartilage turnover. 

However, as a horses gut is somewhat different from a cow’s, in that the hindgut (the equivalent of the rumen) is positioned after the small intestine and not before, there is theoretically less opportunity for these thiomolybdates to be absorbed and ‘cause trouble’.  At least this is what has been largely accepted from previous studies in horses that focussed on plasma copper levels and copper absorption.

However, new blood tests that can be used to measure the activities of key copper dependent enzymes, such as superoxide dismutase (SOD), in conjunction with traditional measurements of plasma copper status and the presence of thiomolybdate complexes suggest that this may not always be the case.  Dr Stewart Telfer of Telsol Ltd, routinely carries out such tests in cattle and has to date analysed about 100 samples in horses suspected of having an issue with molybdenum interactions.  He says, “From our work, it is clear that horses do suffer from molybdenum (thiomolybdate) toxicity.  The interactions between copper, iron, molybdenum and sulphur will take place in the horse’s gut and in certain situations, not always linked to a high molybdenum intake, will result in the horse suffering from molybdenum (thiomolybdate) toxicity.  Dr Telfer however, acknowledges that only relatively small numbers of samples in horses have been tested and the laboratory does not currently have a definitive reference range for horses.
 

Calcium and phosphorus may be mobilized from bone to compensate for ‘acidic diets’
When yearlings first move into training yards, they usually experience a significant change in their diet that has consequences for bone metabolism during this period in their lives when some continued growth occurs and the skeletal system is put under considerable strain.  In general terms, a ‘stud diet’ has what’s called a high dietary anion to cation ratio (DCAB).  This is largely due to the high inclusion of ingredients like soya and forages.  A ‘full race training diet’ on the other hand tends to have a much lower DCAB (is more acidic) due to the reduction in forage intake and higher inclusion of cereals such as oats.  The significance of a low DCAB is that it reduces the efficiency of calcium absorption and retention within the body and may contribute to the reduction in bone density seen in horses in early training.  This surely is an argument for limiting the intake of cereals and maximising forage intake during the early stages of training when a high cereal intake is largely unnecessary. 

Calcium is the most abundant mineral in the horse's body, with the majority being present in the skeletal system.  Phosphorus is also found in large amounts in bone in close association with calcium.  A racehorse’s diet should provide an adequate intake of both minerals but also needs to provide a balanced calcium to phosphorus ratio of near to 2:1.  Although exercise demands a slight increase in calcium intake above the requirements for maintenance, this is usually satisfied by the generalised increase in feed intake.  However, the efficiency with which individual horses absorb calcium varies and should certainly be investigated when a calcium-related issue arises.  This can be achieved by examining an individual horse’s calcium and phosphorus status, by looking at the diet and also within the body using a creatinine clearance test.

Topdressing – a national pastime


When using straight feeds, or when topdressing ‘straights’ onto a ‘balanced’ racing mix or cubes, be aware that certain types of feed are much higher in calcium relative to phosphorus and vice versa (see table).  Alfalfa, with its high calcium to phosphorus ratio, makes an ideal partner for cereals, which are low in calcium relative to phosphorus. 

Conversely, the traditional combination of oats and bran is not ideal, as it combines two feeds, which are low in calcium.  Remember that you can use a supplement or feed balancer to carefully correct any deficiencies or imbalances when feeding straights.  Equally excessive addition of oats to a balanced mix or cube can decrease the calcium to phosphorus ratio sufficiently to cause problems. Most commercial mixes or cubes have sufficiently high calcium to phosphorus ratios to practically be able to withstand the addition of 1-2kg of oats daily, however any increase beyond this is unwise without further corrective measures.

Feeds High in Calcium & Low in Phosphorus 


Alfalfa, Sugar Beet,  Seaweed


 
Feeds Low in Calcium & High Phosphorus

Oats, Barley, Maize, Wheat Bran


Horses have a complex regulatory system, involving certain hormones, for ensuring that the proportion of calcium in the body, relative to that of phosphorus, remains stable and that the level of active or ‘ionised’ calcium in the blood remains within tight limits.  If for one reason or another the level of calcium relative to phosphorus in the blood drops, a number of safety systems will be triggered to redress the balance.  Bone acts as a reservoir of both calcium and phosphorus, which can be drawn on when necessary.  The body's balance of calcium and phosphorus is continually 'corrected' by either conservation or loss of calcium or phosphorus in the urine, via the kidneys or through the skeletal system.   Sustained calcium and phosphorus imbalance can, however, contribute to developmental orthopaedic diseases (DOD) in young horses, or lameness and sometimes bone fractures in mature horses. 

Research shows silicon is a trace mineral worth a second look. Moving on to a less well-recognised trace mineral as far as bone is concerned, there has been some interesting research carried out into the effects of supplemental silicon in the racehorse’s diet. Silicon is a natural constituent of plants and provides structure and rigidity to some of their cell walls.  It therefore forms a natural part of the horse’s diet, however, the availability in horse feed is apparently limited.   Silicon plays a role in the development of new bone and is also important for the calcification process.  It is therefore a relevant micronutrient for horses in training, as bone is dynamic and is constantly undergoing change, in response to forces placed upon it during the training process. 

Research carried out by Dr Brian Nielsen at Michigan State University in the early nineties reported a dramatic decrease in injury rates in quarter horses fed a bioavaiable form of silicon as sodium zeolite A.   This program of research has also established that the silicon is available to foals via the milk of supplemented mares.  However, thus far the group have not uncovered the mechanism by which the beneficial effects of silicon are brought about.  However, the form in which sodium zeolite A is fed (a chalk like powder) and the level of intake used in these studies (about 200g per day for a 500kg horse) makes it impractical to use as a feed supplement unless it can be incorporated within a feed pellet. 

In conclusion, attention to those factors within the diet that support bone turnover is likely to contribute to a reduction in injuries observed, however, the implementation of appropriate training techniques and use of suitable training surfaces also has a huge impact on the durability of horses in training in comparative terms.

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Osteochondritis dissecans - the development, causes and treatments of OCD

One of the most common orthopedic problems encountered in young horses is osteochondritis dissecans (OCD).  This is of particular concern in the Thoroughbred industry, where horses are often bought and sold before maturation is complete and are expected to perform starting at a relatively young age.  There are many common sources of confusion surrounding this disease.  Deborah Spike-Pierce, DVM discusses research into the development, causes and treatment of OCD.

Deborah Spike-Pierce, DVM (13 October 2006 - Issue Number: 1)

By Deborah Spike-Pierce, DVM

One of the most common orthopedic problems encountered in young horses is osteochondritis dissecans (OCD).  This is of particular concern in the Thoroughbred industry, where horses are often bought and sold before maturation is complete and are expected to perform starting at a relatively young age.  There are many common sources of confusion surrounding this disease.  Deborah Spike-Pierce, DVM discusses research into the development, causes and treatment of OCD.

Development


In the most basic sense, OCD is caused by a disruption of the normal growth process of bone. It most commonly occurs in young fast growing animals such as large breed dogs, pigs and horses.  Normally, a cartilage framework in the growth plate at the end of a bone is slowly converted into bone as an animal grows.  If this ossification process is interrupted, the syndrome of OCD can result. There are three major stages of this disease, although the term OCD is commonly used to refer to all parts of the syndrome.  The first phase is osteochondrosis (OC), which is a disturbance of ossification of cartilage into bone resulting in excess retained cartilage.  If this retained cartilage results in inflammation of the joint, this stage is termed osteochondritis.  The inflammation may manifest itself clinically as joint distention or lameness.  Osteochondritis dissecans (OCD) is the stage where a portion of the retained cartilage loosens from the parent bone and forms a fragment.  The separated fragment may remain cartilage or it may ossify into bone.  It is the disturbance of this fragment that can cause the most severe clinical form of the disease by shedding debris into the joint, thus causing synovial effusion and lameness.  Not all horses that develop OC will go on to develop OCD.  In many cases, horses will have no clinical signs and areas of retained cartilage will go on to ossify normally as the horses grow with no long term consequences.


Many different parameters have been described as having an affect on the development of OCD. There is no apparent common denominator in OCD formation and the disease is multifactorial.  Nutritional imbalances, trauma, rate of growth, biomechanical influences as well as genetic predisposition have all been documented as potential causes.


Recent research on the relationship between nutrition and development of OCD have found multiple correlations.  It has been shown recently in the United States that the time of year can affect OCD rates due to spring and autumn peaks in the energy content of the grass.  In studies, horses fed diets with low copper, excess zinc, excess phosphorus and high digestable energy have all shown increased rates of OCD.  There has been an emphasis placed on copper intake, especially in pregnant mares, as copper has been shown to play an important role in the repair of osteochondrotic lesions.  Since mineral content of feed and forage vary throughout the world it is recommended to concentrate on a sound nutritional program since the nutritional contribution to OCD formation itself is multifactorial.


Certain sites in each joint are predisposed for OCD formation.  It is thought that a high mechanical load in areas of thickened cartilage where the blood supply is tenuous can lead to OCD due to traumatic causes.  Conformation may play a role in the distribution of the weight that the horse places on the developing bone.   It has been proposed that horses with a toe-out and upright conformation of their hindlimbs may have higher levels of hock OCDs.  This issue is intertwined with genetics as conformation is influenced by genetics.  Conformational variations can also induce more mechanical stress in particular areas and affect the ossification process via trauma.


Research investigating a possible link between genetics and OCD development is ongoing.  Studies in Standardbreds assessing the prevalence of hock OC have shown heritability rates ranging from 0.25 to 0.52.  These numbers appear significant, however certain warmblood studbooks will not allow stallions with hock OCD into their registry and after 20 years the incidence within the breed has not decreased.  This again supports the claim that OCD is a multifactoral disease.The most recent research on OCD development is at the molecular level.  The focus is on the development and maturation of cartilage, growth factors, collagen types and the expression and metabolism of these factors in bone development.


Osteochondritis dissecans can occur in many different joints but is most commonly identified in fetlocks, hocks and stifles.  Generally, the fetlocks are the first joints affected, followed by hocks, where OCD develops between 2-6 months of age.  OCD of the stifle and shoulder joints usually emerges later, often between 6-9 months of age.  In short, the larger the joint or the longer it takes to ossify, the later OCD develops.  These are the typical windows of susceptibility but since OCD may be traumatic as well as purely developmental in nature the disease may manifest itself at a later time.


Clinical Signs


In many cases, OC and OCD may be clinically silent, with no outward signs that a problem is occurring.  In other cases, there are outward manifestations of the disease.  Fetlock OCD may present as a foal or weanling with persistent distention of one or more fetlocks, with or without lameness.  Radiographs of the affected joints may confirm an OCD lesion.  However, traumatic chip fractures of P1 and sesamoid bone fractures present with similar clinical signs, so radiographs may show those lesions instead.

 
A foal or weanling with hock distention (bog) with or without lameness may also have OCD.  Hock OCD is often bilateral, even if distention is only present in one leg.  High quality radiographs are essential in this diagnosis, since small lesions may cause significant joint distention.


Stifle OCD can have a slightly different presentation, often found in a lame yearling with stifle distention.  Radiographs taken at the onset of the lameness and joint effusion may not show an OC or OCD lesion; it may require several weeks for the lesion to be evident radiographically.  However, even without radiographic evidence of a lesion at the onset of the problem, it is important to restrict exercise because the joint debris causing the effusion may result in significant damage to the articular cartilage with excessive exercise.


Diagnosis

A diagnosis of OC or OCD is most often made from radiographs.  OC lesions are characterized by a lucent area in the bone representing an area of retained cartilage.  OCD lesions often have a similar lucent area as well as the presence of a bony fragment.  However, some lesions are not able to be identified on radiographs and exploratory arthroscopy may be necessary to make the proper diagnosis.


Osteochondrosis lesions occur in specific anatomic sites in horses.  In a stifle, OCD lesions most commonly occur in the lateral trochlear ridge of the distal femur (Figure 1), the medial trochlear ridge of the distal femur and less commonly in the patella.  The most common area of OCD in the hock is the distal intermediate ridge of the tibia (Figure 2), followed by the distal lateral trochlear ridge of the talus and the medial malleolus of the distal tibia.  Fetlock OCD most commonly occurs in the proximal (Figure 3) and distal sagittal ridge of the distal cannon bones.


Since Thoroughbreds are sold at ages ranging from a few months old to adulthood, many variations of this syndrome are seen on survey radiographs.  In young horses, a lucency is often seen where the cartilage in this location has not fully ossified.  Many of these areas  will continue to ossify as the horse matures and not develop OCD.  However, some will go on to develop OCD. This is a grey area purchasers face when buying immature horses.


Treatment


Since there is not a preventive solution for OCD, horses with this disease often need to be treated.  This usually consists of either conservative medical management or arthroscopic surgery.  Conservative medical management has been shown to be successful in very young horses that still have the capacity to heal an OC or OCD lesion.  Regimes may include a modified exercise program, medication, and supportive therapy.  Exercise modification may involve reducing the intensity and amount of exercise (changing from large field to small paddock turnout, for example) or it may be as drastic as stall rest in severe clinical cases.  Medications focus on improving the health of the joint, decreasing inflammation, and augmenting the blood flow to the area of OC or OCD.  Supportive therapy can be as simple as bandaging an effused joint.


If a lesion is non-responsive to conservative management it may need surgical intervention. Surgical treatment is generally the treatment of choice in true OCD lesions that have a flap (versus the OC lesions that characterize the initial phase of this disease).  Surgery is recommended in these types of lesions even if the horse is not showing clinical signs.  It is likely that a true OCD lesion visible on radiographs will become a clinical problem in training and thus require down time for surgical treatment during the training or racing process.  Therefore, it is best removed before the joint is inflamed and further damage occurs.  Prognosis varies by joint but is generally favorable, except in the case of the shoulder joint.


In a study of Thoroughbreds with stifle OCD affecting the femoropatellar joint the affected horses’ overall racing performance was not significantly different than their unaffected siblings.  Fewer of these horses started races at two years old, but there was no difference at three years of age.  The size of a stifle lesion can be a concern when a horse is marketed; however no study has been able to link the size of the lesion with performance.  It is also important to note that the radiographic size of an OCD is not always consistent with the true size identified at surgery because a portion of the OCD is cartilaginous and therefore not identifiable radiographically. 
A study of hock OCD in Thoroughbreds and Standardbreds who underwent arthroscopic removal of the OCD lesion showed the overall racing performance was not different between affected horses and their siblings. The site of the lesion also had no impact in  performance.


There has not been a study published assessing racing performace in horses with fetlock OCD lesions.  However, studies involving multiple breeds show favorable results from surgery.  Ninety perfect of horses who had proximal sagittal ridge OCD lesions arthroscopically debrided returned to athletic activity.


Conclusion
Osteochondritis dissecans can be a confusing and concerning disease.  Although research into its causes is ongoing, there are many effective treatment options available.  Many lesions will heal without requiring surgical intervention and the prognosis for those requiring surgery is generally favorable as well.

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