Racehorse Bone Health
Strong, healthy bones are the foundation for racehorse soundness. Skeletal injuries are a huge cause for concern in the racing industry. Trainers, owners, and vets are constantly looking to improve training programs and identify any potential gaps in the horse’s diet to help minimise and prevent skeletal injuries. To do this it is important to understand how bone is formed and how it adapts with training.
There are many factors involved in the production of strong bones (for example genetics), however, the two key factors that we can influence are nutrition and training. Strong healthy bones cannot develop without a suitable training regime and good nutrition. In this article, we are going to look at bone development and how optimal nutrition, plus appropriate exercise, can positively affect bone density.
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 is comprised 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 it can be replaced by new stronger bone.
- Osteocytes: These cells work to maintain and strengthen the bones when a bone required 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 and calcium makes up 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, but 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. Bone 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 occurs. This results in the osteoclast cells removing the old or damaged bone tissue. In turn this triggers the osteoblast cells to repair the bone by lay 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 take place. Ultimately, this will result in new, stronger bone being formed.
Studies have shown that correct exercise can increase in bone density in the cannon bone, the knee, and sesamoid bones and that 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 have 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, have 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 some of the common issues caused include:
- 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 (strengthen 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 occur 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 therefore 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, they are normally coming from 12-24 hour turn out where they have ability gallop and play. However, once training begins, they are typically stabled from long hours with short intervals of low intensity training. Consequently, bone de-mineralisation can occur. In addition, during this early stage of training bone will undergo a significant degree of remodelling and this process initially makes the bone more porous and fragile before they regain their strength. As a result, research has shown that horses can have reduced bone density during the first 2 months of training, with bones being at their weakest and the horse more prone to issues such as sore shins between at 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 heath, 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), vitamin 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 lysine and methionine, is therefore a key factor in the development of strong healthy bones.
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 calcium to phosphorus 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 in the calcium to phosphorus ratio if required.
Copper & Zinc: Copper is an important mineral for bone, joint, and connective tissue development. Lysyl Oxidase is an enzyme which 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 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 deficient in a forage-only diet 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 resent 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 to increase bone mineral density and thus potential be beneficial for decreasing the incidence of sore shins.
Connolly’s RED MILLS feeds have been specifically formulated to help support bone health. All our feeds provide high quality protein from soya, which is a rich source of essential amino acid such as lysine. Our Pro Balance vitamin and mineral package ensures your horses receive optimal levels and the correct ratios of essential minerals and vitamins such as calcium, phosphorus, copper, vitamins A, D and K.
Supplementation for Bone Health
Young horses in training, those recovering from injury or returning from work following a rest will benefit from additional nutritional support targeted at maintaining improving bone health. In these situations, we recommend adding Foran Equine Osteo-Glycan to the ration. This is a superior powdered supplement containing highly available calcium with a calcium to phosphorus ratio of 2.4:1. It also contains marine collagen, which is rich in type I and II collagen, proteoglycans and glycosaminoglycans all of which aid the bone remodeling process and help to maintain bone health. Chelated copper and zinc, as well as vitamins A and D are included to support bone mineralization. Finally, Foran Equine Osteo-Glycan also includes clinoptilolite, an organic silica, as research has shown that this may positively affect bone density and improve the synthesis of collagen.
Understanding how to increase and maximise bone strength and health by combining appropriate training and good nutrition is crucial. If you have any questions or want to know more about how nutrition can support bone health, get in touch with our team of expert nutritionists.