Feeding a mare in preparation of the breeding season can be a bit tricky. She should ideally have a constant weight going into the breeding season, neither gaining or losing body condition. If she is lactating with a foal at side, this balance can be even more difficult. Lactation produces the highest nutrient requirements of any horse, except maybe the racehorse in heavy training. Nutritional considerations during breeding and pregnancy include:
Body Condition: Broodmares should be maintained at a body condition score of 5 – 7/9. Thins mares, body condition less than 5, tend to have longer gestations, longer estrus cycles, lower pregnancy rates, smaller foals and lower milk production. Fat mares, body condition greater than 7, may have a normal pregnancy and foaling rate, but their feed costs are very high and they have a tendency to develop laminitis.
Energy Balance: Broodmares should be maintained in a positive energy balance, maintaining or just slightly increasing body weight. Non-lactating mares through four months gestation have maintenance level requirements. After this, energy requirements increase until lactation when energy requirements are approximately double that of early pregnancy.
Proteins: Protein requirements are similar to energy requirements, increasing after five months gestation and becoming extreme during lactation when protein is deposited in the milk. Soybean meal is a good supplemental protein source from 2 weeks prior to birth until 7 weeks of lactation.
Minerals: Calcium, phosphorus and magnesium requirements all increase during pregnancy and even more during lactation.
Trace Minerals: Zinc, copper and manganese requirements also increase during pregnancy. Selenium and iodine are also important, but supplementation can tricky because over supplementation can be very detrimental. A balanced mineral and trace mineral supplement, such as a broodmare supplement should be used.
Vitamins: Vitamins A, D and E are the most important for pregnant mares, but should similarly be added as a balanced broodmare supplement.
Feeding Recommendations: Barren, early pregnant and non-lactating mares should be fed maintenance energy levels and should not be allowed to become overweight. During mid-gestation, nutritional requirements are increasing and protein and energy intake should increase 5 to 8%. High quality hay should be the major source of nutrients, fed at 1 – 1.5% of body weight, and a balanced broodmare supplement can be started at this time and fed to label specifications. During late gestation, good quality forage/hay should be continued while supplementing with a high protein (13-15%) broodmare feed and concentrated vitamin and mineral supplement. In the immediate prebirth period, bran or psyillium can be added to the diet to keep feces soft and prevent impaction after birth. Lactating mares will have the highest nutrient requirements and should receive high quality hay, lactating mare supplements with protein, vitamins and minerals and additional fat, if required, from oils or stabilized rice bran.