by: Betsy Wagner, Ph.D. PAS
Department of Animal Sciences, Auburn University

Understanding the protein requirements of horses is helpful in selecting the right type of concentrate to complement your forage source. Last time we reviewed the protein needs of mature, idle horses and those being used for work or performance. This month we will review the needs of broodmares and young growing horses, where the quality and quantity of protein in the diet can have serious impacts on animal health and growth.

Once again, let's assume we have a horse of average body condition with a mature weight of 1,100 pounds. If this horse is a broodrnare, we can expect her to gain almost 150 pounds during gestation. A weanling that is expected to mature to this size is usually about 475 pounds at six months of age, 700 pounds at 12 months, and 850 pounds at 18 months of age. Pregnant mares will easily consume two percent of their body weight in dry matter per day, and lactating mares and growing horses may eat as much as 2.5 percent of their body weight in dry matter.

Selecting a highly digestible, high quality source of protein is important, especially for horses with a high protein requirement such as pregnant or lactating broodmares and young growing horses. Protein digestibility and quality are of greater concern in horses compared to cattle, in that the rumen microbes in cattle are capable of supplying some of the cow's amino acid needs. For the horse, the major site of protein digestion and amino acid absorption is the small intestine, before the feedstuffs ever reach the microbial digestion of the hind gut. While some protein is digested and absorbed in the hindgut of the horse, it is not known how efficient the horse is at utilizing this protein source.

Protein quality as well as quantity is important in choosing concentrates for broodmares and young growing horses. Lysine is the first limiting amino acid, so if lysine is in short supply in the diet, overall protein utilization will be affected. Good sources of lysine, and therefore good quality protein sources, include soybean meal and whey. Legume forages like alfalfa can also be a good source of lysine for adult horses and yearlings with fully developed hindgut.

Meeting protein needs for proper growth begins during gestation. During the first five months, a pregnant mare's needs are not that different from those of a mature, non-working horse with an average level of activity. In months five through eight there is a slight increase in protein needs. The final three months of gestation coincide with a period of rapid fetal growth, and protein and lysine needs increase dramatically during this period. Good quality forage fed with a 12 percent crude protein concentrate at a rate to maintain moderate to fat body condition will generally meet the protein requirements of mid- to late-gestation.

During lactation the mare needs to meet her own maintenance requirements as well as those of the foal she is nursing. Protein content of the mare's milk is greatest immediately after parturition, and peak lactation occurs around 30-45 days post-foaling.

Depending on the quality of forage available a commercial concentrate containing 12-16 percent crude protein and at least 0.7 percent lysine will help meet the mare's requirements. If the foal has access to the mare's concentrate, it should contain 16 percent crude protein in order to meet the foal's needs.

The key to feeding weanlings is providing a high-quality concentrate as their hindgut is not yet able to efficiently digest forages. Their protein requirement seems similar to that of a mature horse, but keep in mind weanlings can only consume about 1/3 the amount of feed of a mature horse. A good quality, highly digestible source of protein such as soybean meal is important in designing diets for these youngsters. When buying a commercial concentrate, look for one with at least 0.7 percent lysine and 14 or 16 percent crude protein depending if the weanling is receiving alfalfa or grass hay.

Yearlings do have a more developed hindgut, and can better utilize the protein in forages. They require more pounds of protein per day compared to weanlings, but they are also able to consume a greater quantity of feed per day. A commercial concentrate with 12-14 percent crude protein usually meets the needs of yearlings when fed to maintain a moderate body condition.


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