Craig Wood, University of Kentucky
The growing period from birth to 12 months of age is a critical time in a horse’s life because 90 percent of mature height and 80 percent of mature weight are achieved during this time. This surge in growth is largely because foals have a high feed efficiency rate that decreases with age.
All young, growing horses have a high requirement for protein, calcium, phosphorous, zinc, and copper for growth and skeletal development. The concentration of lysine in the diet is also important. Soybean meal, canola meal, and animal-source proteins are high in lysine and should be included in the diet of growing horses. In addition, the energy requirement of young, growing horses is higher than can be provided by certain cereal grains and forages. Therefore, a concentrate mix must be fed to meet the requirements. Feeding growing horses a diet low in energy and protein will decrease growth rate and may mask other nutrient deficiencies. However, feeding too much protein and energy may result in rapid growth rate, which increases the incidence of developmental orthopedic diseases (DOD) or skeletal deformities such as osteochondrosis or epiphysitis.
The use of fat as an energy source (10 percent added to grain) has been recommended to decrease DODs; however, the exact mechanism for this effect has yet to be determined. Deficiencies in calcium, phosphorous, copper, and zinc may also cause growth abnormalities. It is also especially important for young horses to consume a diet containing 2:1 ratio of calcium to phosphorous. Providing a trace-mineralized salt high in copper and zinc should alleviate deficiencies in these minerals.
In the nursing foal, milk adequately meets all its nutritional needs for the first 2 months of age and its entire mineral needs for the first 4 months. Within two days, the nursing foal will begin to imitate the mare's behavior and eat hay and/or the mare’s grain, which also provide the foals with nutrients. After two months of age, milk production by the mare decreases, while the foal’s nutritional needs continue to rise. By providing creep feed, which is feed to which only the foal has access, the foal's additional nutrient needs can be met.
Many foals show signs of "post-weaning slump," with which intake and average daily gain decrease. This slump is followed by a compensatory rapid growth spurt (one of the many causes of developmental orthopedic disease). Stress of weaning and the drastic dietary change to solid food have been identified as causes of post-weaning slump. The post-weaning slump can be somewhat alleviated if the foals are creep-fed several weeks prior to weaning. When using a creep feed, use approximately 1 percent of the foal’s body weight per day or 1 lb per month of age. Never provide creep feed free choice to foals, because this can increase the incidence of developmental orthopedic disease and growth-related problems.
Weanlings and yearlings should be fed as individuals. Certain characteristics, such as a variable growth rate, may mean that one horse is more susceptible to developing DOD than another. In both weanlings and yearlings, forages should be provided either by free access to a non-legume hay or restricted feeding of legume hay because of its high energy and protein content. Research has shown that young horses will voluntarily intake a legume hay at a rate of about 20 to 50 percent higher DE than is needed for a moderate growth rate.
The amount of grain to feed weanlings will depend on the quality of hay or maturity of pasture. For weanlings, about 1 lb grain/month of age is a general guideline, with a maximum of 0.7 to 0.9 lb/100 lb mature body weight (7 to 9 lb/d for a 1,000 lb mature weight). For weanlings grazing early-growth pastures, the grain amount may be decreased or eliminated during early pasture growth and added back as the pasture matures and nutritive value of the pasture decreases. The crude protein concentration in the grain should be at least 15 percent when fed to weanlings. Yearlings on a good quality spring pasture may not need grain, but yearlings will need grain during the winter months. Their crude protein requirement is 12 percent but may be higher, depending on the type and quality of forage.