Grass, Yards and Drugs: Uncovering Some Surprising Aspects of Bone Health

Did you know that your horse’s skeleton is continuously influenced by its environment? Bone issues are common causes of lameness, but many of these problems can be avoided by how we manage horses. Bone-related lameness can be linked to training and nutrition, but also confinement, such as stabling, yarding, and stall rest.

Bone is dynamic living tissue, which means it is continuously remodelling through a process called bone turnover. This process involves the coordinated action of bone-resorbing cells called osteoclasts and bone-forming cells known as osteoblasts. Bone turnover serves multiple purposes in horses, including repair of microdamage, adaptation to mechanical loading, and maintenance of mineral balance. In general, the skeleton is strengthened by use and weakened by rest.

Mechanical impact on the bone from moderate exercise, whether it is daily training or simply playing in the paddock encourages osteoblasts to lay down bone tissue, which is converted into healthy, strong bones. When a horse does not exercise regularly, bone renewal slows down and bones can eventually demineralise. Over time, this demineralisation weakens bones, which reduces the strength of the entire skeleton leaving the horse at greater risk of fracture. Regularly exercised horses have stronger skeleton than their stabled peers.

Building Bone and Preventing Injury

A major concern with performance horses is the high incidence of skeletal injury. When the rate of bone adaptation lags with the demands placed on the skeleton—as happens with overtraining, increasing exercise too quickly after a spell, or overuse—microfractures, also known as stress fractures, can occur. These tiny fractures may go unnoticed at first, as some horses do not show any unsoundness. Horses with microfractures are at risk of developing full fractures which can be career-ending and even catastrophic.

Young, growing horses transferred from pasture to yards or stables at the beginning of training may also be predisposed to injury. A decrease in bone mineral density of the third metacarpal (cannon bone) has been demonstrated in young thoroughbreds entering training and housed in small yards and stables. This has not been shown in horses trained out of the paddock, where free access to exercise is likely to provide sufficient loading on the legs to promote normal bone growth. Though horses in paddocks may not run excessively, only a few fast strides per day may be necessary to prevent bone loss associated with limited physical activity available to horses housed in stables. Consequently, paddocked horses may have a skeletal structure that is better prepared for training and competition. Keep this information in mind when housing horses in yards or stables for convenience reasons. Muddy feet may be a small price to pay!

Stall Rest

Stall rest is often necessary during recovery from an injury or disease. In these cases, the reintroduction of exercise needs to be gradual and careful to ensure the bone has adequate time to adapt following a period of inactivity. During confinement, supplements can help combat the negative effects of extended stabling on bone demineralisation. A study by Kentucky Equine Research has shown that targeted supplementation using a combination of bone supporting nutrients coupled with a unique calcium source prevented the loss of bone mineral density in horses confined in stables.

Nutritional Considerations

It goes without saying that all horses must be provided a diet supplying quality roughage and balanced for energy, protein, vitamins, and minerals. Specific nutrients that support bone health include protein, calcium, phosphorus, magnesium, copper, zinc, and manganese. Vitamins C, D, A, and K also work to support bone-remodelling efforts. Correct and balanced nutrition is particularly important when growing and breeding, or for horses grazing tropical pastures, such as kikuyu, or when on certain medications. We highly recommend using an equine nutritionist to assess your horse’s diet and provide individual advice to ensure that their needs are being met.

Kikuyu Pastures

In subtropical areas of New Zealand, kikuyu pasture is common, which comes with advantages and disadvantages. Kikuyu is a productive and persistent warm-season grass that provides good ground cover, tolerates heat, and responds quickly to rain. It also copes well with heavy traffic. Unlike cool-season grasses, kikuyu doesn’t contain fructans, which are indigestible sugars that can lead to hindgut disturbances.

Despite its advantages, kikuyu has a few downsides. Kikuyu tends to dominate other grasses, dries off in winter, and is less digestible than cool-season grasses. However, a key problem with kikuyu relates to calcium and skeletal health. The ratio of calcium to phosphorus in equine diets should be at least 1.5:1, with the diet providing more calcium than phosphorus. Kikuyu is lower in calcium and higher in phosphorus than other grasses, which contributes to body-wide mineral imbalance. The grass also contains oxalate chemicals that bind calcium in the gut, which dramatically reduces calcium digestibility. Both of these factors lead to calcium being pulled from the skeleton to maintain adequate blood levels. As more calcium is removed from bones, they become weaker, which can cause reduced bone density with shifting lameness or fractures and big head disease characterised by enlargement of the upper jawbone.

Supplementing calcium and other minerals is vital in preventing big head disease in horses grazing kikuyu paddocks with large grass intakes. Adding lucerne hay to the diet will help as it has high calcium content. However, a feed or supplement with high levels of calcium, and other trace minerals and vitamins is typically necessary for these horses. If horses do not need extra energy, balancer pellets are an appropriate choice due to their low feeding rate and concentrated nutrients.

Ulcer Treatment

You may not be aware, but ulcer treatment can indirectly and negatively affect bone health. Omeprazole is the most common medication used to treat and prevent gastric ulcers and is widespread across the industry, especially for horses in training. Studies at Kentucky Equine Research have shown horses on omeprazole have reduced absorption of calcium from their diet. Because calcium is a vital substrate for bone growth, it is important to supplement these horses with a bioavailable source of calcium to prevent reduction in bone mineralisation and a weakened skeleton.

Balanced Diet, Balanced Training

Targeted supplementation in conjunction with a balanced diet can help support the growth of strong, healthy bones when used in conjunction with training regimes that match the horse’s level of skeletal fitness. Proper training and supplementation allow bone enough time to adapt to stress. A well-designed program should avoid overtraining with excessively fast works to protect bone health, with adequate rest periods to allow for remodelling, and a gradual increase in training loads after rest.

Equine bone health is a multifaceted aspect of equine management influenced by various factors including nutrition, confinement, training, and grazing practices. Understanding the dynamic nature of bone remodelling and implementing appropriate management strategies is essential for ensuring the long-term skeletal health and performance of horses. By prioritising balanced nutrition and regular exercise, owners can help their horses thrive and hopefully enjoy a lifetime of skeletal soundness.

For a tailored diet analysis or advice on optimising nutrition for bone health, please contact Kentucky Equine Research at [email protected]. For more information about equine nutrition, please click around this website!