Racehorse Bone Health: From a Nutritional Perspective

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. 

By Louise Jones

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.