The University of Kentucky Extension indicates that the body condition of all brood mares should be monitored and their body condition score, or BCS, documented. Mares need to be in good body condition going into the winter so they will be able to rebreed in the spring. Brood mares entering the breeding season should have a BCS of 5 on a scale of 1-9 in which 1 is emaciated and 9 is obese. Pregnant mares going into the winter should have a body score of 6; mares with a body score of 5-6 have ribs that can be easily felt but not seen. A horse with a body score of 7 or greater has ribs that are difficult to feel and being too heavy can lead to a problem with foaling. As pasture declines in the fall, mares will need to be fed hay. You can determine when you need to feed hay by placing some hay in the pasture and if the mares eat it, they probably need it. Also, feeding a little hay early may help to save the pasture and prevent overgrazing.
Many types of hay are acceptable for brood mares but tall fescue should not be used as it can be infected with a fungus that can lead to problems in late pregnancy. Tall fescue is not common in Texas while alfalfa and Bermuda are the most common hays fed to brood mares in Texas. Alfalfa is higher in nutrients than Bermuda so less alfalfa can be fed and also less concentrates will be needed when feeding alfalfa versus feeding Bermuda. Some mares can maintain body weight on alfalfa alone but will need a vitamin and mineral supplement to balance the ration. However, most mares in late gestation, and especially after the foal is born, will require commercial concentrate feeds to supply the energy needed for lactation.