The Nutritional Needs of Brood Mares
Starting your brood mare in good condition supports the health of the foal and its dam throughout foaling and lactation. Weekly Body Condition Scoring (BCS) will help you determine whether all your horses are too thin or too fat, so you can adjust their feed and access to exercise accordingly. For brood mares, keeping tabs on the BCS is especially important. Body Condition Scoring is a system developed in 1980 that allows you, by looking at and feeling your horse to judge the level of body fat on the horse. A horse in moderate condition, whose back is level, whose ribs can’t be seen but are felt and whose tailhead is spongy (indicating fat in the area) has a BCS of 5. Horses with a BCS of 1 or 2 are starved, with little or no discernable body fat: a BCS of 8 or 9 indicates obesity.
A slightly higher than usual BCS at pregnancy gives a mare some leeway, mediating somewhat the demands on her body fat stores by the time she’s nursing a foal so she doesn’t become too thin. Losing too much body fat before or during lactation can diminish the amount and quality of milk, affecting the health of the foal and making it more difficult to get the mare back into condition. Ideally, a mare starts pregnancy with a BCS of 6.5: heavy milkers could go as high as 7.5 BCS, but no higher. The goal is a mare that’s healthily plump—not obese!
Mares put on 70% of their pregnancy weight during the second trimester, (~ 110 days). By the third trimester (270 days), they start to lose weight as the foal develops. The energy that goes into growing the foal is expended on milk after delivery. Ideally, the mare’s BCS at foaling is achieved by the beginning of the third trimester, ~220 days into pregnancy.
Early Lactation (Birth – 90 days)
In early lactation, most mares produce a daily amount of milk equal to 2-3% of their weight. Milk production and quality peak 30 - 60 days after birth: after 90 - 120 days, mare’s milk only provides around 30% of the foal’s nutritional needs. For mares re-bred during early lactation, it’s important to maintain BCS to support both milk production and fertility. With marginal or poor BCS (5 or below), available energy prioritizes lactation, putting the new pregnancy at risk.
Mares should eat 2-3% of their body weight in hay or pasture each day. Alfalfa hay, high in calcium and Vitamin A, is the preferred legume hay. As always, your horses need free access to mineralized salt licks. The best free choice mineral mix for horses on alfafa or clover hay is a 1:1, calcium: phosphorus mix, but with grass pasture or hay, choose the 2:1, calcium: phosphorus mix.
If your mares are on pasture that’s anything less than excellent, additional grain supplementation is required. Expect early lactating mares to eat .75-1.25% of their body weight in grain daily, and make sure to divide the ration into several smaller feedings each day. Heavy milkers may need more grain, or grain with added fat.
Vitamin A has fairly recently been found to play an important part in producing healthy foals. Experts recommend 68,000-81,000 internal Units (IUs) of Vitamin A to supplement the feed of a 1,200 pound lactating mare. Some feeds may contain Vitamin A, but perhaps not in a sufficient amount, so you may have to add Vitamin A supplements.
Late Lactation (90 days – Weaning)
In late lactation, the primary reason to feed your mares grain is to restore body condition. If the mare’s BCS has fallen below 4, she may need grain and even hay if pasture is insufficient. By this time, milk provides a foal with only one-third its nutritional needs, so the main objective is to get the mare back into condition. In early to mid summer, good pasture may suffice.
For mares foaling late in summer, poor pasture quality indicate the need to increase grain intake by 10-15%, and you may also need to feed hay. A lactating mare’s BCS should never fall below 5.5: take steps to increase nutrition if your mare is losing BCS.
Most mares with good BCS in late lactation will do fine on hay and pasture, and if they aren’t pregnant, it won’t hurt them to lose a little weight during weaning. High quality hay and plenty of activity will help the mare to dry off and start putting on weight.
In weaning, it’s preferable to dry up the milk as quickly as possible. Reducing or eliminating the grain ration and providing plenty of exercise stops milk production. Lower quality pasture may also be effective in helping the mare dry off. Obviously, if a mare is in poor body condition (4 or lower) at weaning, you’ll want to take precautions: consult with your vet about dietary issues.
