If you have a mare or mares that you are thinking of breeding, it is a good idea to review their diet and nutrient intakes a few months before they are bred. This gives you time to make any necessary changes and make sure the mare is being fed everything she needs to support a healthy pregnancy. In addition to a good-quality hay and grain ration, here are a few nutrients you may want to consider supplementing in your mare's diet in preparation for breeding.
As in humans, folic acid or folate is essential for the healthy formation of the spinal cord and associated tissues. Grasses tend to be a good source of folate, but if the soil in your area is deficient, your mares may not get what they need for a healthy pregnancy. So unless you've tested your hay and verified that it contains lots of folate, it's a good idea to supplement.
Selenium is a mineral that is important for healthy bones and muscles. A deficiency in foals can lead to a condition called white muscle disease, which can be fatal. Since many soils are depleted of selenium, supplementing is a good idea.
Vitamin A is a nutrient that will be important for the mare's milk production. Although she won't produce milk until the last week or two of pregnancy, it is a good idea to start supplementing early to get her levels up. Vitamin A is a fat-soluble vitamin, so your mare will store vitamin A in her body fat for later use.
Iodine is a nutrient used by the thyroid gland to produce hormones that regulate the metabolism. Mares' thyroid glands become more active during pregnancy, so their iodine needs often increase, which means it is a good idea to supplement. A deficiency of iodine can cause a condition called goiter, which causes the thyroid gland to swell, and you don't want that for your mare or for her foal.
Vitamin E plays an important role in tissue formation, and during pregnancy, your mare will be growing a lot of new tissues. Like vitamin A, this nutrient can be stored in the body fat for later use.
Consider looking for a supplement made specifically for broodmares. Most will contain all of the nutrients above, helping to ensure a healthy pregnancy for your mare and for her foal.
To learn more, contact a resource that carries horse supplements for breeders.