It isn't a good idea for mares to lose body condition before mating. Mares in proper body condition need to have a well-balanced ration. Since pasture isn't available now, feed mares a good-quality grass hay and a 12 percent protein grain mix. Lysine, an amino acid, fed above requirement levels benefited early-pregnant mares. If you feed alfalfa hay, you probably don't need a high-lysine supplement.
Gains increase body fat, resulting in a higher body-condition score.
Mares with poor reproductive conformation may need a Caslick's operation. Mares should have been on a scheduled deworming program from last September until March. If not, deworm them now with a product that protects for 60-80 days. If hooves weren't trimmed regularly during winter, do so now. Lame mares may not be eager for romance.