Regardless of breed, a horse needs a solid nutritional foundation for the development of strong bones and joints. A growing horse’s diet and the correct balance of nutrients have a major impact on this foundation.
Several nutrients are especially important for a horse’s skeletal growth and development. Adequate intake and proper balance of these nutrients are key to optimizing growth and minimizing nutritional orthopedic problems.
Energy and protein
Supporting growth requires an optimal balance of energy and protein. As the horse matures, the growth rate changes, and energy and protein requirements change accordingly. Adequate energy intake is essential for growth and development. Protein quality in the diet is also important. Crude protein in the diet is a measure of nitrogen, not an indication of protein quality. Protein quality is determined by the amino acid composition of the feed and the digestibility of those amino acids. Therefore, the amino acid composition of the diet—not the crude protein percentage itself—is what matters for a growing horse. A steady growth rate can be achieved by avoiding excesses or deficiencies in energy or protein, and this helps reduce the incidence and severity of developmental orthopedic disease.
Excess dietary energy and protein
If certain nutrients in the diet (vitamins and minerals) are unable to support accelerated growth due to excess energy and protein, it can lead to weak or fragile bones, an increased risk of tibial fracture, or deformities. Excess energy also leads to an overweight horse. Excess protein alone has not been found to cause skeletal developmental problems in horses; in practice, however, excess protein usually also means excess energy. Especially in young horses, weight and body condition should be monitored at least monthly and the feeding program adjusted as needed.
Deficiency of energy and protein
Too little protein and energy slows growth rate and may, on the other hand, lead to compensatory growth later when nutrients become sufficiently available again. If energy and protein are not adequately provided during the winter months (due to inadequate feeding, poor-quality hay, etc.), growth slows. In spring, when pastures are lush, growth rate accelerates rapidly. This is called compensatory growth, which can lead to orthopedic problems.
Minerals: calcium and phosphorus
In addition to energy and protein, many minerals are important for proper formation and development of bone and cartilage. Bone contains about 35% calcium (Ca) and 14–17% phosphorus (P). A deficiency of calcium and/or phosphorus can cause thickening of cartilage, slow growth rate, and reduced bone density. While meeting calcium and phosphorus requirements is critical, the ratio in the diet is just as important. The safest calcium-to-phosphorus ratio is between 1.4 and 1.8:1 (Ca:P). Too much calcium can reduce the absorption of other minerals, including iron, magnesium, manganese, phosphorus, and zinc, and thus cause orthopedic problems. Too low a ratio (excess P) can lead to poor bone development, cartilage growth problems, and impaired calcium absorption, which may result in chronic calcium deficiency.
Minerals: copper and zinc
Copper (Cu) and zinc (Zn) are also essential for proper bone growth. Copper is necessary for connective tissue synthesis, while bone contains moderate levels of zinc. Copper deficiencies lead to orthopedic issues, and a lack of zinc in the diet slows growth rate. In general, most feeds and grains are slightly below the horse’s copper requirement, but contain only about half of the horse’s zinc requirement. In practice, the zinc-to-copper ratio in the horse’s diet should be between 3:1 and 5:1. Excess zinc can interfere with calcium and phosphorus absorption and the proper utilization of copper, leading to physitis, lameness, and stiffness.
Vitamins: A & D
Vitamins, especially A and D, are essential for normal growth and development. Beta-carotene, the precursor to vitamin A, is abundant especially in fresh green grass or newly cut hay. Horses must convert beta-carotene into vitamin A in their bodies. Winter storage destroys vitamin levels in hay, especially vitamins A and E.
Vitamin A has many functions in the body. Vitamin A deficiency is unlikely in horses that eat enough green forage. However, horses fed dry or poor-quality hay and/or with very limited grazing time may need vitamin A supplementation. In Finland, many horses require vitamin A supplementation during the indoor feeding season. Vitamin A deficiency slows growth, but it has not been directly shown to cause bone problems in horses.
Vitamin D promotes absorption of calcium and phosphorus from the intestine, resorption of calcium from bone, and reabsorption of calcium in the kidneys. In sunlight, a substance in the skin is converted into a vitamin precursor form and ultimately into an active form in the liver and kidneys. Deficiencies can occur if horses are not exposed to direct sunlight (for example, when blanketed) and do not receive fresh grass. Deficiency can cause various bone abnormalities. Excess intake of vitamin D is rare, but signs of overdose include skeletal abnormalities and calcification of blood vessels, the heart, and other soft tissues.
Summary
The ultimate goal for growing horses is to achieve a steady growth rate and avoid orthopedic problems. This can be ensured by securing adequate nutrient intake in the right balance. Seasonal variation in feed quality and individual body condition require adjusting the feeding program to match needs.
If feed (grain) is reduced, minerals may be needed to correct deficiencies.
Source: Alltech
