Equine Nutrition in the Management of Flexural DeformitiesBy Dr. Peter Huntington · June 21, 2011
Nutrition often plays an important role in the onset of developmental orthopedic disease (DOD) in horses. Deficiencies, excesses, and imbalances of nutrients may result in an increase in both the incidence and severity of physitis, angular limb deformity, wobbler syndrome, flexural deformities, osteochondrosis, and osteochondritis dissecans (OCD). Genetics, environment, body size, growth rate, mechanical stress, trauma, and hormonal factors are also risk factors for DOD.
Flexural deformities are often called contracted flexor tendons, and the young horse is frequently described as “upright” or “uppish.” The functional length of the muscle/tendon unit is shorter than needed to maintain normal limb conformation. These problems may be congenital (present at birth) or acquired during growth, and can involve all four limbs or just the forelimbs. These cases tend to respond quickly to management or veterinary treatment.
Acquired flexural deformities tend to involve the forelimbs and can be unilateral or bilateral. They can involve the deep digital flexor tendon and therefore the coffin joint. The horse will have a raised heel and a club foot. This tends to occur in foals up to six months of age. Older weanlings and yearlings usually suffer from superficial flexor tendon contraction, which means the pastern and fetlock go upright but the heel stays on the ground. In severe cases in which both flexor tendons and the suspensory ligament are involved, the fetlock may knuckle forward. In chronic cases, the tendons and ligaments do not lengthen normally, and these case become more difficult to treat.
There has been no specific research on the role of nutrition and flexural deformities, but we think that nutritional factors such a mineral deficiencies, mineral excesses, mineral imbalances, and dietary energy excess can be involved as risk factors. In addition, feeding practices such as overfeeding grain, inappropriate grain for forage/pasture, and inadequate mineral and vitamin fortification can lead to an increased incidence of DOD. Minerals of importance are calcium, phosphorus, copper, zinc, and manganese. Rapid growth is a key risk factor for many forms of DOD, especially flexural deformities.
Proper nutrition of the broodmare is a vital factor in minimizing the risk of flexural deformities, especially during mid to late pregnancy. The foetus begins to develop rapidly after seven months of pregnancy, and its nutrient requirements become significantly greater than the mare's maintenance requirements; therefore adjustments should be made in the mare's diet. Digestible energy requirements only increase about 15% over early pregnancy. Protein and mineral requirements increase to a greater extent. This is because the foetal tissue being synthesized during this time is quite high in protein, calcium, and phosphorus. Trace mineral supplementation is also very important during this period because the foetus stores iron, zinc, copper, and manganese in its liver for use during the first few months after it is born. The foetus has developed this nutritional strategy of storing trace minerals during pregnancy because mare's milk is quite low in these elements.
Mares in late pregnancy are often overfed energy in an attempt to supply adequate protein and minerals to the developing foal. Fat mares may have a greater incidence of foals with angular limb and flexural deformities. If the pregnant mare becomes fat during late pregnancy, she should be switched to a feed that is more concentrated in protein and minerals so that less can be fed per day. This will restrict her energy intake while ensuring that she receives adequate quantities of other key nutrients.
The most critical stage of growth for preventing DOD is from about three months to one year of age, when the skeleton is most vulnerable, and when nutrient intake and balance is most important. Weanlings should be grown at a moderate or optimum rate with adequate mineral supplementation. In temperate regions, the contribution of pasture is often underestimated, leading to excessive growth rates and DOD with only moderate grain intakes.
Environmental factors are a key risk factor with flexural deformities. Hard ground or poor hoof trimming that leads to foot soreness and lameness is thought to contribute to many cases of weanlings and yearlings going upright. The same situation can apply with conformational defects that lead to physitis or uneven loading patterns on joints and bones. This can lead to pain and the development of flexural deformities. Restricting exercise, applying heel wedges, and using nonsteroidal anti-inflammatory drugs are strategies designed to reduce leg pain in young horses with contracted tendons.
Excessive growth is commonly associated with many types of DOD, and in the case of flexural deformities, growth spurts in weight or height are commonly seen prior to the horse going upright. Regular monitoring of height and weight and interpretation of changes using a growth-tracking program identifies at-risk horses before they go upright.
The goal of a feeding program for young horses is to reduce or eliminate the incidence of DOD. Unfortunately, it will still occur in some foals. Nutritional intervention can help reduce the severity of many forms of DOD, but not all of the damage resulting from DOD is reversible. However, it is important to alter the feeding programs of foals with flexural deformities or other DOD. The type of alteration will depend on what risk factors are identified, but changes tend to follow a similar pattern. In almost every instance, energy intake should be reduced while maintaining adequate levels of protein and minerals. The rationale for this type of modification is that skeletal growth should be slowed, but adequate substrate should be available to promote healthy bone, muscle, tendon, and ligament development.
Grain should be removed from the diet, and pasture/hay intake restricted to a level supplying around 75% of the foal's normal energy requirement. This restriction, however, should not compromise protein and mineral intake, so a different type of feed will be required. Just feeding hay and chaff will lead to a diet deficient in minerals and vitamins. The best approach involves the use of a low-calorie, low-intake balancer pellet. This would be fed at approximately 2.2 lb (1 kg) per day for a weanling or yearlings with a mature weight of 1,000-1,300 lb (450–600 kg) and supplies key amino acids, minerals, and vitamins missing from the forage. This type of diet will reduce growth rate and body condition and assist in resolving the flexural deformity whilst still supplying the nutrients needed for development of the skeleton and connective tissues. This type of supplement is typically fortified with 25-30% protein, 2.5-3.0% calcium, 1.75-2.0% phosphorus, 150-175 ppm copper, and 375- 475 ppm zinc. This is an extremely useful type of supplement to correct underfortified rations for all types of horses.
With time and good management, many cases of flexural deformities can be rectified so that surgical treatment options are not required. Early action is vital as the longer the condition is present, the more difficult it is to treat.