Craig Wood, University of Kentucky
Energy is the most important nutirent when balancing a diet for breeding stallions and broodmares. Energy for reproduction is defined as energy that is required for maintenance plus the process of reproducing. During the off-season, when a breeding stallion is not breeding or a broodmare is in the first eight months of gestation, the requirements will be the same as a horse at maintenance. It is during the active breeding season or during late gestation through lactation that energy requirements will increase.
The stallion’s nutrient requirements are very similar to the nutrient requirements for maintenance. The primary difference is the need for increased energy. The actual energy that the stallion needs for reproduction is small (i.e., sperm production), but the energy for the physical activity associated with breeding is large and variable from stallion to stallion. Some stallions will become very excitable and prance around prior to and after breeding a mare, whereas others do not. Therefore, it is common for the breeding stallion to be fed a diet higher in energy to maintain a desirable body condition score and behavior. Stallions should always have access to forages, either pasture or hay. If grain is needed, a good rule is no more than 0.75 lb/100 lb body weight (0.75 kg/100 kg) should be provided to meet the stallion's energy requirements. Adjustment in this rule should be made to maintain desirable body condition. High-energy dense grains such as corn or oils at 10 to 20 percent can be added to the diet to increase the energy density, if necessary. However, individual stallions will respond differently to increased energy. Some stallions may become more difficult to handle when fed a high-energy diet. Adjustments in amount fed should be based on behavioral response and body condition. Some evidence suggests that vitamins C and E can enhance reproductive efficiency. A balanced diet, in most cases, will provide all the necessary vitamins for proper reproductive function.
Feeding the broodmare can be simplified with a basic understanding of the four nutritional stages of reproduction in the mare. These stages are early gestation, late gestation, early lactation, and late lactation. Embryonic or fetal development requires little or no additional nutrients during the first eight months, when the mare’s diet can be formulated similarly to a maintenance diet. So, no grain supplement is needed during early pregnancy if forage is adequate in quality and quantity. The nutritional goal during the first eight months of pregnancy is to allow the mare to store body fat for use later during late gestation and lactation without allowing the mares to get too fat (body condition score of more than 6 to 7). It is desirable that mares show moderate to moderately fleshy condition by parturition. Although fatness does not appear to affect the actual act of parturition, it can affect foal growth by decreasing milk production.
During the last three months of gestation, fetal growth rapidly increases, thus increasing nutrient requirements. Energy, protein, calcium, and phosphorous needs increase during this time. Pregnant mares will need to be fed a more energy-dense feed to meet increasing requirements. An average to high-quality legume, such as alfalfa, or grass cut or grazed at early maturity, may provide adequate energy and protein. If the mare is consuming adequate amounts of this high-quality hay or pasture, no grain supplement is necessary. However, many mares may not be able to physically consume enough hay or pasture to meet their nutrient requirements, and the inclusion of a concentrate may be necessary. In feeding broodmares, it is important to maintain a proper calcium and phosphorous ratio in their diet. A proper Ca:P ratio of at least 1:1, but preferably 1.5 or 2:1, is desirable.
Broodmares grazing or being fed endophyte-infected fescue prior to the last trimester of pregnancy should be placed on another pasture or fed a different type of hay. Endophyte-infected fescue can cause reproductive abnormalities, such as abortions, agalactia (lack of milk production), prolonged gestations, and abnormal placentas.
A mare can produce up to 3 percent of her body weight in milk per day during early lactation, and 2 percent per day during late lactation. In addition to a twofold increase in energy needs, mares also need an increase in protein, calcium, phosphorous, and water. If a good-quality legume hay such as alfalfa is provided, the protein requirements should be met, but the energy requirements will not. Therefore, a concentrate will need to be provided that includes a high-energy grain source such as corn or oats. After three months of lactation, the mare’s grain amount should be decreased by about half. This should be followed by a gradual decrease in grain up until about one to two weeks prior to weaning the foal and a decrease in forage to about 1.5-2.0 lb/100 lb body weight. By decreasing total intake of energy, there will be a decrease in milk production by the mare, which forces the foal to adjust to eating solid food and prevents the mare from getting too fat. If the mare is too fat, the best time to implement a weight loss program is two weeks prior to weaning or during early gestation. A program of weight loss should not be started prior to breeding, during the first trimester, or during early lactation. Thinness may affect conception rates and reproductive efficiency in open mares, and it decreases colostrum and milk production in lactating mares.
Keeping mares at a moderate to fleshy condition is more economical than trying to put weight on thin mares during the breeding season. It requires more energy to put fat on a thin mare than to maintain a mare in a body condition score of 6 or 7. During the last trimester of pregnancy, the mare should be fed adequate amounts of nutrients to allow for normal fetal development. During lactation, mares must be fed to regain any body condition lost during pregnancy and to meet the demands of milk production.