Racehorse Bone Health: From a Nutritional Perspective

By Louise Jones

Strong, healthy bones are the foundation for racehorse soundness, but unfortunately skeletal injuries are an issue that every trainer will face. There are many factors involved in the production of strong bones; however, two key factors that we can influence are training and nutrition. 

Every trainer knows how important exercise is to ‘condition’ the bones, and we are constantly striving to improve training programmes so that sufficient strain is applied to signal an increase in bone development, whilst not straining the bones to the point of fracture; this is a difficult balancing. Perhaps more fundamental to this is the role of diet in supporting bone density, strength and repair.  Even minor nutrient deficiencies or imbalances can mean that the horse doesn’t receive the nutrients it requires for healthy bones and thus increases the risk of potential problems down the track.

Understanding how bone is formed and adapts in response to training, alongside the critical role optimal nutrition plays in these processes, can help to ensure skeletal soundness and minimise the risk of bone-related injuries.

Bone formation & remodelling

Bone formation occurs by a process of endochondral ossification; this is where soft cartilage cells are transformed into hard bone cells. Bone consists of three types of cells and an extracellular matrix. This extracellular matrix is made mainly from the protein collagen, which makes up to 30% of mature bone and is a key element in connective tissue and cartilage. The three types of cells in bone are:

• Osteoblasts: These are the cells that lay down the extracellular matrix and are responsible for the growth and mineralisation/hardening of bone.

• Osteoclasts: These cells are involved in the breakdown of bone, so that it can be replaced by new stronger bone. 

• Osteocytes: These cells work to maintain and strengthen when a bone requires modelling or remodelling.

Bone mineral content (BMC) is a measure of the amount of mineral in bone and is an accurate way of measuring the strength of a bone. Interestingly, about 70% of bone strength is due to its mineral content; calcium being the most notable and accounting for 35% of bone structure. A horse’s bones do not fully mature until they are about 5-6 years old. So, whilst a horse will have reached 94% of their mature height when they are a yearling, they will have only reached 76% of their total BMC. 

Although it may seem like mature bone is inert, it is in fact a highly dynamic tissue, and BMC is constantly adapting in response to exercise and rest by a process called remodelling.zBone remodelling is a complex process involving several hormones and nutrients. Essentially when mature bone ages or is placed under stress, such as exercise, small amounts of damage occur. This results in the osteoclast cells removing the old or damaged bone tissue. In turn, this triggers osteoblasts and osteocytes to repair the bone by laying down collagen and minerals over the area, thus strengthening the bones. It’s estimated that 5% of the horse’s total bone mass is replaced (remodelled) each year. It should be noted that during the remodelling process, bone is in a weakened state. Therefore, if during this period, the load applied to the bones exceeds the rate at which they can adapt, injuries such as sore shins can occur.

Bone strength & exercise

When galloping, a horse places up to three times its body weight in force on the lower limbs. The more load or pressure put on a bone, the greater the bone remodelling that will need to take place. Ultimately, this will result in new, stronger bones being formed. 

Studies have shown that correct exercise can increase bone density in the cannon bone, the knee and sesamoid bones; and this can help reduce the likelihood of skeletal injury. However, the intensity of training is key; low intensity exercise (trotting), whilst essential for muscle development, has been shown to only result in small change in cannon bone density. Whereas training at high speeds for a short amount of time (sprinting), rather than repetitive slow galloping, has shown to result in a significant increase in bone density. This is highlighted in a study using a treadmill where short periods of galloping at speeds over 27mph (43 km/hour) were associated with a 4-5% increase in the density of the cannon bone.

Whilst exercise clearly plays a pivotal role in bone density, doing too much too soon can be disastrous and result in issues such as:

• Sore/buck shins: This is a common injury in young racehorses. It is caused by excessive pressure on the bones resulting in tiny fractures on the cannon bone, which may not have fully mineralised (strengthened and hardened). This results in the periosteum (a fibrous membrane of connective tissue covering the cannon bone) becoming inflamed. 

• Bone chips: Another common skeletal injury in racehorses, mostly seen in joints, particularly in the knee. This is when a tiny fracture occurs in the joint, weakening the bone and ultimately resulting in a ‘chip’ of the bone becoming separated. 

When trying to maximise skeletal strength, periods of lower intensity exercise or rest are just as important as gallop work, as they give the bone a chance to remodel. However, prolonged rest will have a negative effect on skeletal health.  Research has looked at the loss of BMC in the cannon bone when horses were placed on box-rest (with 30 minutes on the walker) and found overall BMC was reduced. Therefore, even horses returning to work after a short period of 1-2 weeks of box-rest could potentially have a significant decline in bone density and thus be at increased risk of skeletal injury once exercise recommences. 

It’s also important to bear in mind that when a young horse starts training, it is normally coming from a 12–24-hour turnout. This is where the horse has the ability to gallop and play. However, once training begins, they are typically stabled from long hours with short intervals of low intensity training. Consequently, bone demineralisation can occur. In addition, during this early stage of training, bone will undergo a significant degree of remodelling in response to exercise. Initially this process makes the bone more porous and fragile before it regains its strength. As a result, research has shown that horses can have reduced bone density during the first few months of training, with bones being at their weakest and the horse more prone to issues such as sore shins between day 45–75 of training. 

It should be noted that even when training is carried out slowly, conditions such as sore shins can still happen as bone remodelling occurs at different rates in every horse and is influenced by factors such as track surface and design. While there is some information on exercise and bone development from which to make inferences, a definitive answer as to the perfect amount of exercise to support optimal bone development has not yet been found.

Nutrition & bone health

Exercise is essential to bone health, but nutrition plays an equally important role. Bone is continuously being strengthened, repaired and replaced. And if we can aid bone remodelling with good nutrition, we can decrease the likelihood of skeletal injury. The essential nutrients for bone health are protein, minerals and vitamins, including calcium (Ca), phosphorus (P), zinc (Zn) copper (Cu), vitamins A, D and K. 

Protein: Collagen is a protein and forms the bony matrix on which minerals are deposited. Feeding sufficient high-quality protein, rich in essential amino acids such as lysine and methionine, is therefore a key factor in the development of strong healthy bones. When selecting an appropriate feed for horses in training, both the level and quality of the protein it provides should be carefully considered; not all protein is equal.  

Calcium & Phosphorus: It is well documented that these essential minerals are the foundation of strong and healthy bones, making up 70% of the BMC. The ratio of calcium and phosphorus in the diet is also very important for bone mineralisation. This is because imbalances in the Ca:P ratio can result in the removal of calcium from the skeleton and may lead to bone demineralisation. The minimum Ca:P ratio in the diet should be 1.5:1, with the ideal ratio being at least 2:1 for young horses. It is important to note that adding other feedstuffs such as chaffs or cereals to the horse’s feed can alter the Ca:P ratio in the overall diet. For example, adding oats, which are high in phosphorus, will reduce the calcium to phosphorus ratio and this may adversely affect calcium absorption. On the other hand, including some alfalfa, which is high in calcium, can help to increase the Ca:P ratio if required. 

Copper & Zinc: Copper is an important mineral for bone, joint and connective tissue development. Lysyl oxidase is an enzyme that requires copper. It is responsible for cross-linking of collagen, and therefore copper plays an important role in the formation of new bone which requires a collagen matrix. Similarly, zinc is integrally involved in cartilage turnover; and research has shown that horses supplemented with zinc, as part of a complete mineral package, have increased bone mineral density compared to horses fed an unsupplemented diet. Copper and zinc are frequently found to be low in forage and therefore must be provided in the form of a hard feed or supplement. 

Vitamins: A number of vitamins play essential roles in skeletal health. For example, vitamin A is involved in the development of osteoblasts—the cells responsible for laying down new bone—whilst vitamin D is needed for calcium absorption. More recent research has also shown that feeding vitamin K improves the production of osteocalcin, the hormone responsible for facilitating bone metabolism and mineralisation. Furthermore, research in two-year-old thoroughbreds suggests that feeding vitamin K may help increase bone mineral density and thus potentially be beneficial for decreasing the incidence of sore shins. Although standard feed manufactures include vitamin A and D in their feeds, a few also now include vitamin K.

Supplementation for bone health

Young horses in training, those recovering from injury or returning to work following a rest will benefit from additional nutritional support targeted at maintaining improving bone health. In these situations, supplementing with elevated levels of calcium and phosphorus will help improve bone health. Look for a supplement containing collagen, which is rich in type I and II collagen, proteoglycans and glycosaminoglycans—all of which aid the bone remodelling process and help to maintain bone health. Choosing a supplement that also contains chelated copper and zinc, as well as vitamins A and D, will also help support bone mineralisation. 

In summary, skeletal injuries have a huge adverse effect on the racing industry and are a common cause of lost training days. Undoubtedly, adapting our training regimes, modifying our gallops and improving our management practices will all help to reduce the risk of bone-related injuries. Equally, the role of nutrition in bone health should not be overlooked. A balanced diet, rich in nutrients, minerals and vitamins, can contribute significantly to bone density and strength. Proper nutrition is an essential parameter of skeletal health, participating in both the prevention and treatment of bone diseases.  To achieve a strong, sound skeleton, you must feed the bones.

The Importance of forage testing

Forage (hay/haylage) is an important source of nutrients for horses in training. However, the levels of minerals such as calcium, phosphorus and copper present can vary enormously and depend on factors such as the species of grass and the land on which it was grown. It is recommended that you regularly test the nutritional value of your forage. This will highlight any mineral excess/deficiencies and allow for the ratios of certain minerals such as calcium and phosphorus to be assessed. In most cases, any issues identified can be corrected through using an appropriate hard feed and/or supplement.

Gut Health - Aspects of bad behaviour and how to fix it

By Bill Vandergrift, PhD

When performance horses behave or react in ways that are less than desirable, we as trainers and handlers try to figure out what they are telling us.  Is there a physical problem causing discomfort, or is it anxiety based on a previous negative experience? Or, is the bad behaviour resulting from a poor training foundation leading the horse to take unfamiliar or uncomfortable situations into their own hands? This usually triggers the fright and flight reflex instead of relying on the handler for direction and stability.  

Often when the most common conditions that cause physical discomfort are ruled out, it may be tempting to assume that the bad behaviour is just in the horse’s head or that the horse is just an ill-tempered individual. In my experience, most unexplainable behaviour expressed by performance horses is rooted in the horse’s “other brain,” otherwise known as the digestive system. In this article, I will explain what causes poor digestive health, the link between digestive health and brain function, and what steps can be taken to prevent and/or reverse poor digestive health.

Digestive health

While most trainers are familiar with gastric ulcers, symptoms and common protocols utilised to heal and prevent them, there still remains a degree of confusion regarding other forms of digestive dysfunction that can have a significant effect on the horse’s performance and behaviour. In many cases, recurrent gastric ulcers are simply a symptom of more complex issues related to digestive health.  Trainers, veterinarians and nutritionists need to understand that no part of the horse’s digestive tract is a stand-alone component. From the mouth to the rectum, all parts of the digestive system are in constant communication with each other to coordinate motility, immune function, secretion of digestive juices and the production of hormones and chemical messengers. If this intricate system of communication is interrupted, the overall function of the digestive system becomes uncoupled, leading to dysfunction in one or more areas of the digestive tract.

For example, a primary cause of recurrent gastric ulcers that return quickly after successful treatment with a standard medication protocol is often inflammation of the small and/or large intestine. Until the intestinal inflammation is successfully controlled, the gastric ulcers will remain persistent due to the uncoupling of communication between the stomach and lower part of the digestive tract.

How do we define digestive health? Obviously, digestive health is a complex topic with many moving parts (figuratively and literally). The main parts of a healthy digestive system include, but are not limited to 1) the microbiome, 2) hormone and messenger production and activity, 3) health of epithelial tissues throughout the digestive system, 4) normal immune function of intestinal tissue and 5) proper function of the mucosa (smooth muscle of the digestive tract) to facilitate normal motility throughout the entire length of the digestive tract.

Microbiome is key

A healthy and diverse microbiome is at the centre of digestive health. We now recognise that reduced diversity of the microbiome can lead to digestive dysfunction such as colic and colitis, development of metabolic disorders such as insulin resistance, reduced performance and increased susceptibility to disease. Research efforts leading to greater understanding of the microbiome have recently been aided by developing more sophisticated techniques used to identify and measure its composition in horses, laboratory animals, pets, livestock and people. While these research efforts have illustrated how little we really understand the microbiome, there have been significant discoveries stemming from these efforts already.  For example, a specific bacteria (probiotic) is now being used clinically in people to reverse depression resulting from irritable bowel syndrome (IBS). Bifidobacterium longum NCC3001 reduces depression in IBS patients by directly affecting the activity of the vagus nerve which facilitates communication between the brain and the digestive tract. It should be noted that Bifidobacterium longum NCC3001 has been demonstrated to be more effective at reducing depression in IBS patients than antidepressant drugs commonly used in these same cases. While we do not commonly recognise clinical depression as a physiological condition in horses, the same mechanisms that affect the function of the vagus nerve and brain chemistry in IBS patients can affect a horse’s behaviour and reactivity due to intestinal dysfunction, resulting in a horse that bites, kicks, pins its ears or otherwise demonstrates hyper-reactivity for no apparent reason, especially if this behaviour is a recent development.

One case in particular I dealt with years ago that had underlying suggestions of depression in a horse, and underscores the importance of a diverse and healthy microbiome for performance horses, was a horse that had been recently started in training and was working with compliance on the track. The problem was this horse seemed to be unable to find the “speed gear.” The trainer had consulted with various veterinarians, physical therapists, chiropractors and others in an attempt to pinpoint the cause for this horse’s apparent inability to move out; and it was everyone’s opinion that this particular horse had the ability but he simply wasn’t displaying the desire. In other words, he was “just dull.”  After reviewing this horse’s case and diet, I had to concur with everyone else that there was no obvious explanation for the lack of vigor this horse displayed on the track even though his body condition, muscle development and hair coat were all excellent. Despite any outward signs of a microbiome problem other than the horse’s “dullness,” I recommended a protocol that included high doses of probiotics daily, and within 10 days, we had a different horse. The horse was no longer dull under saddle; and when asked to move out and find the next gear, he would readily comply; by making an adjustment to the microbiome, this horse’s career was saved.

There is always a change to the microbiome whenever there is a dysfunction of the digestive system, and there is always digestive dysfunction whenever there is a significant change to the microbiome. Which one occurs first or which one facilitates a change in the other may be dependent upon the nature of the dysfunction, but these two events will almost always occur together. Therefore, efforts to maintain a viable and diverse microbiome will reduce the chances of digestive dysfunction and increase the speed of recovery when digestive dysfunction occurs.

Leaky gut

Even though the physiological basis of leaky gut has been understood for some time, leaky gut has not been a condition recognised to affect behaviour, performance or health in horses until recently. Today, leaky gut is quickly becoming a recognised dysfunction of the digestive system that has a multitude of negative effects on the overall well-being of horses including allergies, insulin resistance, uncharacteristic behaviour, picky appetite and reduced performance. As illustrated in Figure 1, leaky gut refers to a breakdown of the structures, referred to as tight junctions that hold adjacent intestinal cells together.

When the small and large intestines are healthy, the tight junctions between individual intestinal cells remain closed, forming a barrier between the inside of the intestinal lumen and the inside of the horse’s body. This barrier normally serves as a very important function by preventing complex molecules such as undigested proteins and carbohydrates as well as pathogenic and non-pathogenic bacteria from “leaking” through the intestine and entering the horse’s blood stream. Also note in Figure 1 that as you move your focus from left to right in the diagram, not only do the tight junctions become open, but the intestinal cells become more and more inflamed, eventually leading to total breakdown of the intestinal cells themselves. At this point, you not only have leaky gut, but now the condition has progressed from a leak to a flood, so to speak. This illustrates that the severity of leaky gut can vary from mild to severe with increasing severity also being associated with increasing intestinal inflammation.

Figure 1. Basic Physiology of Leaky Gut

 Image Courtesy of Kemin Industries.

As the severity of leaky gut increases, the communication between the different components of the digestive system is disrupted, and the coordination between the different sections of the digestive tract becomes uncoupled. The production of hormones such as serotonin and dopamine is altered, which has a direct effect on digestive function and brain function concurrently. This is one of the most obvious reasons why intestinal inflammation causes a horse’s behaviour and temperament to change.  Inflammation of intestinal cells initiates a self-propagating process that stimulates additional inflammation of the intestine and initiates systemic inflammatory processes throughout the entire body.  The self-propagating nature of intestinal inflammation is the reason why horses don’t just simply recover from it without assistance. In fact, I have worked with individual horses that have suffered from leaky gut for years based on their case history. The longer leaky gut has existed, the longer it will take to reverse in most cases.

In addition to leaky gut causing changes in behaviour and performance, leaky gut can also alter immune function and metabolic status. There is growing evidence that the initial cause of insulin resistance in many horses is in fact leaky gut. Intestinal inflammation causes a marked change in glucose homeostasis, which in turn reduces insulin sensitivity. Unfortunately, it appears that once insulin resistance is established, it is near impossible to reverse completely even if the leaky gut condition that caused it in the first place is successfully reversed.  

Leaky gut is also a common trigger for allergies in horses. It is well known that the majority of the horse’s immune system is located in the intestine. When the intestine “leaks,” undigested proteins, bacteria and other immune-stimulating agents gain access to the bloodstream, thus putting the immune system on high alert. Many horses respond to this situation by presenting with multiple allergies, many of which are reactive enough to warrant immunotherapy (allergy shots). I often hear in these situations that “my horse is allergic to everything”; and in many instances, this would seem to be the case. Fortunately, by reversing leaky gut and removing these immune-stimulating agents from the horse’s body, many of these allergies simply disappear. Keep in mind that horses can in fact be truly allergic to certain feeds and environmental agents, and these allergies have nothing to do with digestive health. It is best to consult with an experienced veterinarian and nutritionist to distinguish between true allergies and those caused by an overactive immune system triggered by leaky gut.

As illustrated in Figure 2, leaky gut can be caused by many different “triggers.” In performance horses, the most common triggers for leaky gut are: 1) stress (physical and emotional), 2) intense exercise, 3) heat stress and 4) various medications. Of these, stress is the strongest trigger for leaky gut due to the fact that stress of any kind increases circulating levels of cortisol. Cortisol breaks down the tight junctions of the intestine, which in turn results in leaky gut.

Figure 2.  Possible Factors Causing Leaky Gut in Horses

Preventing and reversing leaky gut

Almost all performance horses will present with digestive dysfunction or leaky gut at some point in time in their career. The reason is simple: stress is the strongest trigger for leaky gut, and all performance horses experience stress to one degree or another. Unfortunately, there is no exclusive marker for leaky gut at the present time. Researchers are getting close to developing a reliable diagnostic test for leaky gut as this article is written, but in the meantime it is best to detect digestive dysfunction and leaky gut by evaluating changes and observing symptoms presented by the horse. A partial list of symptoms to look for includes: a) not performing to the previous level or level that is expected, b) change in personality (e.g., grouchy or “leave me alone” behaviour, c) resistance to leg aids especially on right side (right dorsal colon is often inflamed), d) backing ears or biting when being saddled especially when the cinch is tightened, e) dull, f) prefers to eat hay rather than grain, g) manure has a funny odor or consistency, h) low fecal pH (herd specific), i) constantly shifting weight from one hind leg to the other in the stall, j) tight and “sunk in” in flank area, k) tight in back and hamstrings, l) eating a lot of grain but not gaining weight, m) dull coat and/or skin disorders, n) poor hoof quality, o) multiple allergies, p) improves while on omeprazole but quickly reverts when taken off, q) recurrent or chronic diarrhea and r) irreconcilable behaviour. (Note: No two horses will present with all of these symptoms or the same symptoms, but this list provides a guide for the most common symptoms to evaluate.

Since stress is the strongest trigger for intestinal inflammation and leaky gut, steps should be taken to remove as much stress as possible. For example, paying attention to biosecurity measures, transporting at times and with methods that reduce stress, adjusting training schedules to avoid heat stress and overexertion are things that can be done to reduce stress. Keeping forage (hay and/or pasture) in front of horses 24/7 is critical. Controlling the amount of grain-based feed fed per day can help in many cases. As a guideline, if you are having to feed more than 7 kgs (or 15 lbs) of grain per day to maintain a horse’s condition and energy level, you should suspect digestive dysfunction as one of the reasons so much feed is required.

If you suspect your horse is presenting with leaky gut, how can you help reverse it? Begin by continuing to provide “good quality” forage 24/7 and utilise a high-fibre, high-fat, low-soluble carbohydrate feed in place of a grain-based feed.

Second, utilise nutritional tools that are now available to stimulate closure of the tight junctions. These include nutraceuticals such as butyric acid, glutamine, bioactive peptides (plasma or colostrum), specific probiotics such as Bacillus subtillus PB6 and carnitine. There are products available currently that provide one or more of these nutraceuticals in the proper dosage.

Third, support a diverse and healthy microbiome with the use of probiotics and prebiotics. When selecting probiotics, numbers matter! It is preferred that any probiotic strain be dosed at a minimum of 1 billion CFUs (colony forming units) per day. Be sure to understand that this is per strain and not cumulative for a mixture of different probiotic strains. I would rather administer 10 billion CFUs of a single probiotic strain than 5 billion CFUs of a product containing a mixture of seven different strains.  Additionally, for optimal effectiveness of any probiotic, it is imperative that it be dosed in combination with prebiotics such as yeast cultures, mannan-oligosaccharides, fructooligosaccharides, or inulin, for example. Prebiotics and probiotics work synergistically to alter the diversity and overall activity of the microbiome in a manner that provides far superior results compared to either one by itself.

Fourth, provide anti-inflammatory activity to the intestine with omega-3 fatty acids. Flaxseed, chia seed, hemp oil, and fish oil all contribute to reducing inflammation in the intestine. The omega-3 fatty acid EPA from fish oil is especially effective as an anti-inflammatory agent for the intestine. DISCLAIMER:  In cases of severe leaky gut and severe intestinal inflammation, omega-3s may exacerbate the inflammation rather than reduce it. This will be noted within just 2–3 days by the horse presenting with notable diarrhoea. Additionally, omega-3s and coconut products are contraindicated for horses presenting with severe or chronic diarrhoea, as this is usually a reliable symptom of severe leaky gut, which is often made worse by these dietary components.

Fifth, include nutraceuticals to improve production of intestinal hormones and provide additional protection for intestinal cells. Possible choices include liquorice, slippery elm, aloe, arginine, citrulline, theanine, tryptophan, or alpha lipoic acid. Consult with a reputable supplement company for suggestions on which products and dosage are appropriate for your horse.