Dangers of Overfeeding
There is more than one way to reach certain goals, yet there are absolutes every horseman should keep in mind when feeding young horses. First, the foal is a potential athlete. Management decisions and nutrition early in life can have major effects on performance potential as an adult. Secondly, his most rapid growth phase is from birth to weaning, and any mistakes you make at this stage of his life may be greatly magnified. His requirements must be considered and supplied in a way to meet his needs and to optimize his genetic potential for growth and performance (rather than compromise them by inadequate nutrition or by overfeeding). Some breeders find that overfeeding defeats their purposes in growing larger youngsters; once a foal starts getting too fat, he may not grow as tall. Optimum growth occurs when the foal continues to grow in height, without becoming fat.
Many breeders select for early maturity, which results in fast growth, heavier muscling and more body condition (which results in more fat) at an earlier age. This has been a major contributing factor in increased incidence of skeletal and leg problems in young horses. It's also difficult to correctly balance a ration when you are feeding maximum amounts, since excessive amounts of one nutrient may hinder proper absorption of another. The combination of fast growth (early maturity) and an unbalanced diet caused by overfeeding accounts for a high percentage of the skeletal defects seen in young growing horses.
A foal grows rapidly his first months, often gaining 2.5 to 3 pounds a day; the nutrition he gets at an early age will determine his growth rate. A foal that is underfed or on an unbalanced diet with serious deficiencies will take longer to reach mature size and weight. If mineral imbalances are so severe that his bones do not grow properly, he may never quite reach full potential. Generally, however, the main effect of underfeeding is slower growth and later maturity. At the other extreme, overfeeding can make the youngster too fat and heavy (putting too much stress on growing bones and joints) or push him to maximum growth, creating defects in the skeletal system -- and bone lesions that may cause unsoundness later.
Many foals today at the age of 6 months have obtained about 45 percent of their mature body weight, 84 percent of their height, 75 percent of their heart girth measurement and about 80 to 90 percent of their bone growth. Rate of growth declines as the youngster matures. Body weight gain is the major growth factor in the weanling period, rather than skeletal growth. In young animals, skeletal growth comes first (suckling foals make the most bone growth), then muscle (weanling phase), then fat. A growing animal gains skeletal size first, then fills out, adding muscle and fat. If a young animal adds body mass too quickly on the growing frame (as can happen when overfed), the extra weight puts too much stress on immature bones.
In the past several decades, horsemen have been pushing foals to faster growth, expecting more from them than in earlier times. Growth rates of light horse (as compared to draft horse) breeds in reports prior to 1945 stated the average foal attained 40 percent of mature weight by 6 months, 60 percent by 12 months, and 72 percent by 18 months. A young horse in 1925, for instance, would have been expected to weigh 400, 600 and 720 pounds at 6, 12 and 18 months of age, respectively, if he was to mature at 1000 pounds.
The average growth rates of foals in reports from 1969 to 1981 were 45 percent, 66 percent and 81 percent of mature weight by 6, 12 and 18 months (meaning that youngsters maturing at 1000 pounds would weigh 450, 660 and 810 by these ages), and many horsemen were feeding for even faster rates. This kind of growth rate began to create problems in the form of skeletal and joint deformities that were unheard of in earlier years. These problems are still plaguing horse breeders today.
Feeding practices have changed dramatically since the early days when horses were allowed to grow up slowly and normally; in recent years much greater amounts of grain are fed. Textbooks in the early 1900s suggest that weanlings be fed unlimited amounts of hay, and 2 to 5 pounds of grain daily. By the 1980s, weanlings were more apt to be fed 7 to 10 pounds (or more) of grain, and less hay. When their energy and protein intake increases, growth rate increases, and the demand for nutrients needed for bone formation is thus also greatly increased.
The daily calcium requirements of a foal fed only 2 pounds of grain is much less than for a foal fed 12 pounds of grain. It is much more critical that the ration be properly balanced, especially for minerals, when foals are growing rapidly. The more rapidly a foal grows, the higher his mineral requirements to build a larger, faster growing skeletal frame. The concentration of nutrients needed in the grain or supplements will depend on the kind and the amount of hay being fed, and the amounts of hay and grain being fed will also depend on the desired rate of growth.
A mare that milks well gives her foal properly balanced and adequate nutrition, without him needing any other feeds than good pasture or good hay -- if the mare is fed a balanced diet containing her nutrient requirements. Milk produced by the mare increases in quantity the first 2 months, then begins to decline. The protein and energy content of milk start to decline also. This fits the foal's needs, since his requirement for energy and protein is highest his first 2 months of life. After he starts eating other feed, his needs are partly supplied by pasture grass, hay or grain.
During the first few months, the foal's digestive system is dependent on milk. Mare's milk is relatively low in trace minerals, but the foal has adequate stores in his liver (if the mare had proper nutrition during pregnancy). His stores of copper, for instance, will last up to 13 weeks. After that he'll need to get much of his trace minerals from feed. The foal is generally eating a fair amount of forage by then, and most forages (pasture and hay) contain adequate amounts of trace minerals. If a foal is pushed for fast growth, however, eating grain and concentrates, the feed must contain an adequate amount (in proper balance) of the minerals he needs, since faster growth will increase those needs.
Heavy milking mares, fed a lot of concentrates, sweet feed or supplements to increase milk production, may increase a foal's risk for skeletal problems, since his appetite may be satisfied by milk . He'll eat very little grain or supplement himself --continuing to grow rapidly in height and weight -- and be short of minerals. Mineral content of the mare's milk drops as lactation progresses. Mares that have produced foals with DOD (developmental orthopedic disease -- which can include a number of bone growth disorders) should have their rations drastically reduced.
At various times during the past two decades, nutritionists have blamed high protein levels, excess calories and various mineral imbalances for creating skeletal problems in young horses. However, they now realize bone and joint problems are usually not caused by any one of these factors alone, but an imbalance among them. For example, if high protein and energy levels speed a foal's growth while the minerals necessary for bone development are in short supply, DOD may result. Foals fed too much grain, or weanlings on low protein grass pasture and high-energy grain mixes that are not balanced for minerals, are also at risk.
Most horse owners feed mares and foals grain, but not all of them need it. In fast-growing foals, it may be harmful. Nursing mares and growing foals should never be underfed, but it's just as unhealthy to overfeed. This can mean too much feed (especially grain) or too much of a specific nutrient such as protein, carbohydrate, calcium or phosphorus.