Nutrition of the broodmares affects the reproductive efficiency of the mare: milk production, health of the foal, rebreeding efficiency, and long term reproductive performance. Mares can be divided into 4 classes when thinking about nutritional needs: 1.) the maiden mare, 2.) the barren and early pregnant, non-lactating mare, 3.) the mare in the last trimester, and 4.) the lactating mare.
The maiden mare is a diverse group of mares that includes young mares that are still growing, mares retired from performance and mares that were unsuitable for performance. Young growing mares need additional energy, protein, calcium and phosphorus to maintain proper growth. Mares that are in thin condition because of training need to be fed to be gaining weight.
Barren and early pregnant, non-lactating mares have the same requirement as mature horse at maintenance, The most common mistake is to overfeed mares in early pregnancy. The goal during early pregnancy is to maintain good body condition.
The copper content of the mare's diet in late pregnancy directly effects fetal bone development. Selenium is important in muscle function. The lack of Se in soils used to grow forages may lead to white muscle disease in foals. Only limited amounts of Se cross the placenta so pregnant mares should be supplemented from late gestation through lactation, or foals should be supplemented at birth. Mare's milk is known to be low in Se so injectable Vitamin E and Se may be given after birth.
The lactating mare has the highest nutritional requirements of any class of horse except for the training race horse. Mares produce 3% (1-12 weeks) to 2% (13-24 weeks) of their body weight in milk. The mare requires 792 kCal to produce a kg of milk (2.2 lbs.) as well as Ca, P, and other trace elements. Energy intake is critical in lactating mares and may be limiting to reproductive efficiency.
The nutrition of the broodmare should be guided by body condition. Below are the NRC nutritional requirements of broodmares and examples of rations which would fulfill the requirements.