Why bucked shins are so prevalent in the racehorse

Article by Adam Jackson MRCVS 

One of the most common causes of lost days to training and racing in racehorses is dorsal metacarpal disease (DMD), often referred to as “bucked shins” or “sore shins.” 

Often a frustration to trainers and owners, this problem rears its ugly head at the time of highest expectations, such as arising the last day of work before a horse’s first race, right after a horse’s first victory or after a horse was purchased at a two-year-old sale.

This disease presents with heat, pain with or without inflammation (swelling) on the dorsal (front) surface or the dorsomedial (front inside) surface of the third metacarpal bone (cannon), which is referred to as acute periostitis. With rest and reduced exercise, the condition can improve, but catastrophic fractures of the cannon may occur at the site of previous DMD episodes. A good understanding of this disease and strategies of prevention are vital in order to improve the welfare of the horse and reduce the potential expenses to all shareholders.  

Introduction

The cannon bone is an important structure in the weight bearing and absorbing shock. As the horse moves, the bone bends a little and then returns to its original shape like an elastic band, which is often referred to as elastic deformation. In addition, it has been observed that horses that work slowly have tension on the front of the cannon bone; in other words, the bone is stressed by a stretching force rather than a compressing force. However, at higher speeds, these forces change from stretching to compressing forces.

Repeated bending forces (stress cycle) on the cannon bone causes dorsal metatarsal disease. When the horse is young, it has a thin bone cortex. As the horse grows and is repeatedly subjected to these forces, the bones remodel and the cortex thickens, making it stronger. However, if the bending forces exceed the bone’s ability to remodel, then this leads to stress fatigue and bone damage.

The occurrence of bucked shins is most common when horses are developing, typically at two to three years old as training becomes more intensive. But it must be noted that if the horse is not bone fit, any aged racehorse is susceptible to these diseases when they begin training. Roughly at the age of five years, when a horse is fit, they are at a low risk of this disease. Within the first six months of training, DMD may present in one or both front limbs. If the condition does occur in both front limbs and the horse is being trained on a circular track, then it is likely the inside leg is where it will occur first. In other words, if the training tends to be in a counterclockwise training circuit, then there are greater forces on the left limb than the right, thus the left is more likely to develop the disease before the right limb.

Risk Factors of DMD

1. Age: DMD occurs most commonly in two to three-year-olds often within their first six months of training. It is rarely seen in horses with a mature skeleton (age four and over). However, this disease has been seen in five-year-olds especially if they have been stalled for a long amount of time after weaning and not racing until that age.

2. Gender: It is believed that the gender of the horse does not alter its risk to DMD.

3. Breed: Most common in Thoroughbreds but may be seen in both Standardbreds and Quarter horses. 

4. Genetics: The risk of DMD is influenced by genetics as variation in limb bone geometry (inherited) behaves differently to force/strains on the bone. In addition, the longer the cannon bone, the greater the load is at flexion of the dorsal cortex of the bone, making it more susceptible to DMD.

5. Training and racing surfaces: The different types of training and racing surface alter the risk to DMD because there are variations in the force applied to limbs as well as the acceleration rates of hoof impact.  Furthermore, the impact of these forces is increased with greater speed.  Dirt tracks tend to be the hardest surface, whereas synthetic tracks reduce hoof and limb impact and loading force. However, it is important to remember that the hardness all of these surfaces can be altered by a number of other factors such as:

Training and racing surfaces

• Different surface materials

• Changes in weather, temperature and humidity

• Surface maintenance (i.e., soaking, harrowing)

• Changes in horse body weight

• Age of surface, wear and tear of surface

• Human opinion of condition of track

  6. Training: The length of time for bones to respond to different training practices is unknown. Although further research is required, it is suggested that fast work should be avoided in the early stages of training as it is thought that high-speed exercise introduced too quickly (within one month) was detrimental to bone health.

  7. Direction of training: Track direction varies globally. Thoroughbreds tend to lead with the inside forelimb around turns then switch to the outer forelimb on the straight. It has been suggested that due to greater forces on the leading limb on the turn, that limb is more at risk of bucked shins. However, more research is required to make accurate conclusions.

  8. Speed: Current research is contradictory. Some research indicates a reduction in the risk of DMD if the horse is trained at high speeds with every extra mile worked, and canter work increases the risk. However, other research suggests that short periods of work (< 1 month) at high speed increases the risk of DMD.

  9. Camber: In the U.S., tracks are usually flat in contrast with European tracks, which tend to vary in their design and often include slopes, twists, turns, uphill sections, and cambers, with turf being the prevalent surface.   In addition, races may be run straight, clockwise or counterclockwise.  Although it is known that this variation in track characteristics alters the horse’s gait, thus altering forces on the forelimbs, further research is needed to understand if these variations increase the risk of DMD.

How does DMD develop?

Bucked shin is the formation of tiny stress fractures on the front or inside of the cannon bone of the horse’s front legs. DMD occurs when the stress on the legs with high-speed training exceeds the bone’s ability to adapt to those stresses. 

Bone is a dynamic tissue that is constantly adapting its structure. Once the bone is formed in immature animals, the bone grows and changes shape by a process called modeling. Bone remodeling is different to modeling in that its function is to renew the skeleton and involves both bone resorption and formation to occur at the same location in a sequential manner.   

With high-speed training, there is high-strain fatigue, which causes excessive compression of the bone. During this compression, there is an insufficient amount of bone remodeling at the point of stress. At this site, this new bone is much weaker; thus, it is susceptible to inflammation, and pain and may lead to fractures.

Treatment of dorsal metacarpal disease

Treatment of DMD is designed to alleviate pain and inflammation while allowing the remodeling process of the bone to catch up with the damage that has been caused from stress cycling.

The core of the treatment is rest and providing pain relief, followed by a slow and gradual increase in exercise levels. 

Fractures of the bone cortex can be treated with surgery using lag screw fixation and osteostixis. Osteostixis is the drilling of many holes around the site of fracture in order to promote bone healing. Lag screw fixation is the drilling of a screw across the fracture line to compress and stabilize the bone. However, fracture recurrence is common with both techniques and requires five to six months out of training.

There are additional treatments that may be used to complement core treatments. Extracorporeal shock wave therapy (ESWT) is commonly used for treatment and involves a highly concentrated, powerful acoustic (sound) energy source being applied to the site of injury. The rationale is that ESWT increases blood flow, increases growth of new blood vessels and increases the production of natural healing factors in the treated area. The research findings are limited on its effectiveness but anecdotally among the veterinary profession, it seems to work on bucked shins and stress fractures. 

In North America, horses are not permitted to race or breeze for 30 days following treatment as per the Horseracing Integrity and Safety Authority’s (HISA) rulings. In Europe, horses must not have had shock wave therapy on the day of racing, or on any of the five days before the race day in which the horse is declared to run. 

With all treatment options, there must be a careful and considered discussion with the veterinarian and all stakeholders on the desired outcome while bearing in mind the important factor of the horse’s welfare and wellbeing.

What about bisphosphonates?

Some clinicians are using a combination of shockwave and bisphosphonates (TildrenTM, OsPhosTM) to treat DMD. Bisphosphonates were first seen in human medicine and used for osteoporosis. Bones are constantly remodeling in a process that removes old bone cells and deposits new ones. Bisphosphonates help prevent bones from losing calcium and other minerals by slowing or stopping that natural process that dissolves bone tissue, thus, helping bones remain strong and intact. Veterinary surgeons report mixed results with these therapies, and long-term use of bisphosphonates is expensive and has serious consequences. Bisphosphonates are toxic to the gastrointestinal and renal systems, thus, potentially causing colic and kidney disease. Their safety has not been evaluated for the use in horses younger than four years old nor in pregnant and lactating mares.

RULES ARE CHANGING - Bisphosphonates

HISA’s Anti-Doping and Medication Control (ADMC) Program came into effect on March 27 and with it, new regulations regarding the presence and use of bisphosphonates.

The Horseracing Integrity & Welfare Unit (HIWU) states “The ADMC Program regulations categorize bisphosphonates as a banned substance, meaning that they are prohibited from being administered to, or present in, covered horses at any time. Covered horses that test positive for bisphosphonates under the ADMC Program are subject to lifetime ineligibility, and associated covered persons may incur an Anti-Doping Rule Violation.”

“HIWU will not pursue disciplinary action against Covered Horses or their associated covered person(s) for the presence of bisphosphonates if the covered person(s) can provide documentation (e.g., medical records or a positive test result) to HIWU of the administration or presence of bisphosphonates prior to the implementation date of the ADMC Program.” 

In Europe, bisphosphonates are not to be administered to a racehorse under the age of three years and six months as determined by its recorded date of birth, on the day of the race or on any of the 30 days before the day of the race in which the horse is declared to run as per The International Federation of Horseracing Authorities rulings.

Training Regimens

With DMD, it must be remembered that it is an appropriate response for new bone formation when the cannon endures cyclic stress and injury. This injury cannot be ignored but addressed to reduce the risk of serious consequences.  Exercise is the root of the problem; therefore, the solution is to alter the patterns of exercise.   

Dr. David Nunamaker, DVM, of the University of Pennsylvania, has developed a training program, which is believed to reduce the risk of DMD. The rationale when developing this modified training program is that horses are not born with the right bone structure for racing.  The bones are to develop and adapt to racing. By providing training programs that mimic racing, the bones can adapt to the forces that are applied during racing, thus, reducing the risk of developing bucked shins.

When initiating this training regimen, it is assumed that young horses are broken to ride in autumn and able to gallop a mile by January so that training can start. 

Stage 1 (5-week duration) – Horses finish the gallops two times a week with the last 1/8th of the mile (last 200 meters of 1600 meters) completed in an open gallop in 15 seconds.

Stage 2 (5-week duration) – Twice a week, open gallops for ¼ of a mile (400 meters of 1600 meters) in 30 seconds including a one-mile (1600 meters) gallop.

Stage 3 (7-week duration) – The addition of speed work once per week.  Breezing (moderate speed) for ¼ mile (400 meters) and daily gallops lengthened to 1¼ miles twice per week for four weeks. In the following three weeks, the ¼ mile breeze is continued with a strong gallop out for another furlong (roughly 40 seconds total for a breeze). 

Conclusion

The findings of exercise research are often varied and contradictory due to many research variables, making comparisons and conclusions difficult. In addition, most of the research of musculoskeletal issues in racehorses uses racing data, but most injuries occur during training.

Because more research is needed, there remain conflicting views of the effects of racing on horses before skeletal maturity and the most effective and safe way to introduce speed exercise. At present, the data suggests that distance and speed should be implemented gradually and should include high-speed work at full racing speed.

The racing industry must continue to work cooperatively to address the welfare concerns associated with horses experiencing DMD.

What We Need to Know from HISA

Keeping up with the legal evolution of HISA is like playing monopoly onboard a ship in pitching seas—the players, tokens and money are strewn all over the deck.

Article by Annie Lambert

When the Horseracing Integrity and Safety Act (HISA) went into effect on July 1, 2022, few people involved with the Authority or stakeholders operating under the new rules could have predicted the political path the statute would trudge down.

Specifically, HISA’s Anti-Doping and Medication Control (ADMC) rules, which were to go into effect January 1, 2023, were put on hold. If/when enacted, the Horseracing Integrity & Welfare Unit (HIWU) will handle daily operations and administration of the ADMC. Drug Free Sport International will conduct the drug testing.

Multiple legal challenges from multiple entities in multiple jurisdictions snarled any further implementation of HISA. There were cheers from those opposing the new rules and jeers from those looking forward to implementing national uniform safety rules and anti-doping and medication control rules for Thoroughbred racing in the United States.

Race trackers took issue with the fact that they had little to no input in the rules and implementation of HISA. The Authority responded by creating the Horsemen’s Advisory Group (HAG). The group is composed of 19 owners, trainers and veterinarians along with representatives of racing offices, backside employees, farriers and aftercare enterprises. They began meeting monthly last November and will serve one- to two-year terms.

While the HAG may have settled some issues for horsemen, the legal suits continue. HISA appears confident that their legislation—which was written by legal experts specifically adept in constitutional law—will remain intact. 

The Politics

Dating back to early 2021, the lawsuits against HISA have been detailed ad nauseam. While the courts have knocked down some suits, a few remain standing at this time. All challenges include some variations of the constitutionality of the legislation regarding specific regulations, with others challenging the assessment formula, definitions, search and seizure regulations and/or FTC enforcement and other specifics. 

In mid-November, just six weeks prior to implementation of the ADMC, the United States Court of Appeals for the Fifth Circuit ruled HISA to be unconstitutional. The court felt that the legislation delegated unsupervised government power to a private entity. HISA rules are authorized by the Federal Trade Commission (FTC), which the court felt should provide closer supervision and have more input into the legislation.

Judge Joseph Hood, of the Sixth District Court, sided with the federal government on December 7 2022, suggesting the legislation established clear boundaries on HISA’s power, including a requirement that all rules be approved by the FTC. There is no timetable set for the court’s final decision.

On December 12, the FTC disapproved of proposed ADMC rules as submitted. The designated, independent enforcement agency of the ADMC program (HIWU) was prepared to enforce anti-doping and medication rules on January 1, 2023, if approved by the FTC. 

The FTC denied approval of the program rules “without prejudice” due to pending legal uncertainties. HISA will be resubmitting the ADMC rules. During the interim, state law will govern medication issues. The suspension of the ADMC also puts a hold on assessments that would be used to fund the program.

Kentucky Senator Mitch McConnell wrote a quick, short-worded clarification of HISA that was submitted with the recent Omnibus bill and passed the Senate on December 19 2022. The fix gives the FTC the power to “abrogate, add to, and modify the rules” of HISA as they see fit. The Omnibus bill passed the House of Representatives the following day, and President Biden signed it into law on December 29.

Legal wranglers for HISA have since asked a federal appeals court to set aside its ruling that declared the Authority unconstitutional in light of the legislation’s rewrite by Senator McConnell.

The Assessments

Much of life seems to come down to money; it may not be the root of all evil, but it does guide a lot of policy.

When the FTC did not accept HISA’s proposed ADMC in mid-December, state-owed payments due to fund the Authority were put on hold. Roughly $58.1 million in payments for 2023 are currently pending legal outcomes. The majority of those assessments pertain to the launch of the anti-doping program that has also been put into a holding pattern. Assessments already incurred for 2022 are required to be paid by the state commissions and the racetracks.

HISA’s total budget for the current year (2023) is slightly north of $72.5 million. That number includes nearly $37.4 million for operating the HIWU and drug testing work to be done by Drug Free Sport International.

A staff of 35 full-time employees will be in place by the end of this year, charged with implementing sound collection protocols and working to maintain continuity with existing collectors. They will also work on testing operations, compliance, quality assurance, education and industry outreach, good relations with state racing commissions and collaboration with laboratories, investigations and technology. 

The budget for 2023 provides $18.7 million for lab and research expenses toward implementing the ADMC program. 

State racing commissions received their assessed HISA operational expenses last October. Using a methodology set by HISA and approved by the FTC, the formula is calculated from total starts and the percentage of purses paid of total United States purses, other than the Breeders’ Cup World Championship races. 

States given the top assessments by HISA are New York ($8,660,471), Kentucky ($7,445,145), California ($7,344,139), Pennsylvania ($6,611,479) and Florida ($6,445,226). Payments are due in monthly payments; and if state commissions do not pay their assessments, their expense is passed to the racetracks. In states with multiple tracks, each track will be charged with a portion of the obligation based on a proportionate share of starts.

State racing commissions are able to reduce their assessments if they negotiate with HISA and HIWU and choose to provide sample collection personnel and investigative services in compliance with new ADMC program rules. HISA has provided $23 million to fund these racetrack contributions.

The Strikes

The HISA crop, or whip, regulations have created some turmoil. The consequences for overuse during a race can be stringent. 

Crop regulations (which also apply to exercise riders during morning workouts) have been in effect since July 1 2022 as part of the Integrity and Safety Authority. The main source of contention regarding the rules is striking a horse during a race more than six times. 

For seven to nine strikes during a race, jockeys face a one-day suspension plus a fine of either $250 or 10 percent of their share of the purse, whichever is greater. But strikes exceeding nine are punishable by more severe consequences. Those infractions do not alter the pari-mutuel payouts but can lead to a horse losing its total share of the purse money distributed to the owner, jockey and trainer. 

Ten to 13 strikes results in a $500 fine to the rider or his share of the purse, whichever is greater, plus a three-day suspension. At 10 or more strikes, the horse is also disqualified.

Graded stakes, including Breeders’ Cup races, are no exception. A recent Breeders’ Cup jockey struck his mount seven times – just one strike over – and received a one-day suspension and was assessed three points on his license as an additional penalty.

HISA rules created a point system for multiple violations by repeat offenders that will eventually have penalties compounded. Riders with 11 to 15 points on their license would receive an additional seven days of suspension in addition to the newest penalty. Riders with 16 to 20 points receive an additional 15-day suspension. With 21 or more points, a jockey could get a full 30-day “vacation.”

Points expire over six to 12 months post-violation; expirations are decided on a sliding scale based on the violation class assigned to those infractions.

Riders have acknowledged that keeping an accurate count of their hits can be difficult. And there are situations when use of a crop might keep a horse from causing a dangerous situation, e.g., drifting in or out. Several top jockeys have also noted that the extreme penalties give them cause to be more cautious of the regulations.

One jockey, who was listed in the standings where he was riding, was given a 30-day suspension when stewards said he showed a lack of effort, a “lackluster” finish, not consistent with his usual riding style. It sounded like a cloaked suggestion that he had pulled his mount. The rider, who did not appeal, reported that he thought he had reached his six-strike limit.

The National Jockeys’ Guild filed litigation against HISA, which they have recently dropped. There are purportedly ongoing negotiations with concern on rules, which HISA seems willing to negotiate to some degree. 

Whip violations are handed out after the race card is over. The stewards review race video prior to issuing the rulings. Both jockey and owner will have an opportunity to appeal.

The Contraband

There are two basic lists of drugs within the ADMC rules: “banned substances” and “controlled medications.” The FTC, of course, has not approved this portion of HISA, and there are only guesses as to when it will be put to use. 

During the interim, state regulators will continue to be responsible for medication rules, drug testing and enforcement.

In the past, trainers and veterinarians have relied on suggested withdrawal times to decide how far ahead of a race to give a particular drug. The new rules do not rely on withdrawal times. Federal laws, as written, require the Authority and HIWU to base medication rules on international standards for racehorses.

Foreign countries base their medication rules on the International Federation of Horseracing Authority guidelines, which do not provide withdrawal times. Instead, they provide “detection times.”

Detection times are based on peer-reviewed studies of a drug. In the study, a sample of horses are all given a drug and tested at periods of time afterwards. The detection time is the first time point at which all the horses in the study were negative for the drug given.

Due to variations in how drugs are metabolized in individuals, the detection times are a starting point for vets and trainers to decide when to withdraw a drug. Based on the individual horse, dosage and how it was administered the connections to the horse must be aware the outcome may change due to the variables.

If the lines between legal dosages and overages are so fine, it could lead one to assume racing officials would prefer horsemen not use the drug at all.

One trainer was suspended for seven calendar days, fined $3,000 and assessed two points on the Association of Racing Commissioners International scale for multiple medication violations for a lidocaine positive. Testing showed the horse had tested above the allowed amount of a “permissible medication.”

The involved horse was disqualified from the Maiden Special Weight race win and the purse redistributed. 

Shoeing regulations have been a big issue with trainers and farriers from the get-go. The initially approved shoe dimensions were not manufactured, and those dimensions eventually changed several times. It left horsemen confused.

The federal regulation that prevents the use of toe grabs on front shoes became an issue again when connections of a second-placed horse in a Gr. 2 stake questioned if the winner had front grabs. It was determined the winner was shod legally. The finish stood.

Horses are commonly trained in different shoes than those they run in. Blacksmiths and examining veterinarians who see horses with prohibited shoes in the morning are said to be making trainers aware there would most likely be a problem if the horse were to race as shod. 

The voided claim is another regulated area that was foreign to some racing jurisdictions, while a state like California has been practicing for some time. 

HISA policy requires claims be voided if a horse is unsound in the test barn, experiences bleeding or has a post-race medication violation. These rules are in addition to policies many tracks had in place to void claims, such as a horse dying on track or having to be vanned off. To date, most voided claims were a result of post-race unsoundness or horses that bled.

In spite of legal frustrations and rules that horsemen feel are too restrictive and not beneficial to the Thoroughbred racing industry, HISA marches on. More horsemen being involved should help, but the learning curve seems too long for everyone in racing.

Prohibited Substances Overview

• Banned substances prohibited at all times, such as anabolic agents and diuretics or masking agents

• Banned methods prohibited at all times, such as chemical castration or immunocastration

• Controlled medication substances prohibited during the race period, such as analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs)

• Controlled medication methods prohibited during the race period, such as the use or administration of an alkalinizing agent

• Prohibited substances and methods may be included in the prohibited list by general category or with specific reference to a particular substance or method. 

The prohibited list will be updated yearly.

Lazarus’ Lessons Learned

Lisa Lazarus, the chief executive officer for the Horseracing Integrity and Safety Authority (HISA), pointed to the importance of sport-wide unity within the United States racing industry. Lazarus spoke during the Global Symposium on Racing held in early December at the University of Arizona in Tucson.

A year after taking her position with HISA, Lazarus pointed to 10 lessons she has learned:

1. Racing’s strength is the diversity of viewpoints, which creates a lot of debate among industry leaders.

2. Participants in the industry have a role in making HISA better, even those groups that have been critical of the Authority. That was her reason for adding the Horsemen’s Advisory Group to include all viewpoints in the rulemaking process.

3. Criticism is expected and welcomed from the people who make a living at the track with skin in the game. 

4. Stakeholder’s engagement, even criticism, is welcomed and will help make HISA and the industry better. 

5. The vulnerability of jockeys, who must trust that the system has reduced the risk of injury to horses and riders, will be able to depend on jockey health initiatives via the racetrack safety program.

6. Despite robust debate regarding the Authority, the racing industry has wanted uniform medication regulation for years. Racing participants who compete fairly deserve to know their competition is also competing fairly.

7. The sport of racing has tried independent regulation because a voluntary system has not worked.

8. Uniform rules must be accompanied by uniform implementation to work successfully.

9. The Authority’s regulators should not be the focal point for the sport. They should be operating in the background to root out those with bad intentions, leaving the industry a focus on integrity.

10. The Authority has incredible people who are committed to doing what is best for the industry. The intent is not to complicate people’s lives, but to help grow the industry through uniformity.