Preparing for Baby – Nutrition of the Mare in Late Gestation

Spring is just a couple months away, bringing warm sunny days, green grass and newborn foals, but, we must get through winter first. Winter poses some nutritional challenges for pregnant mares because this is the time when they transition from mid to late gestation. Duringthe first 7 or 8 months of gestation, the fetus grows very slowly, approximately 0.2 lbs per day, so early pregnancy doesn’t present a big nutritional challenge to the mare. Dry mares in early gestation can be fed like any other mature, idle horse. When kept on green pasture or good quality hay with salt and a vitamin/mineral supplement, early gestation mares often don’t require additional grain to meet their nutritional demands.

However, during the last 3 – 4 months of pregnancy, the foal begins grow and develop more rapidly. In fact, during the last 90 days of pregnancy, developing foals gain approximately 1 lb per day. Considering the average foal weighs 100 – 110 lbs at birth, 90 of those pounds happened in the last 4 months of gestation. This rapid development requires significant nutritional support to lay down the foundation of bones, muscles and tendons. The only way to provide this nutrition to the fetus is through the mare so it is critical to provide her with the proper balance and quality of protein, vitamins and minerals during this time. The increased size of the growing foal also takes up room in the mare’s body cavity such that she may actually eat less hay or forage. This reduction in forage intake, coupled with the increased nutritional needs, means mares in late gestation should be supplemented with a nutritionally-balanced concentrated grain ration. Even in situations where forage alone is maintaining mares in acceptable body condition, it is important that they receive quality concentrate supplementation. While good quality forage may be able to provide sufficient calories to maintain body condition of the mare, other nutrients such as protein, vitamins and especially trace minerals, will be deficient.

While body condition certainly affects reproduction efficiency and health of the mare, having mares in good condition doesn’t guarantee proper foal development. Body condition is directly correlated with calorie intake but doesn’t necessarily reflect intake of protein, vitamins and minerals. Research has shown that foal birth weight can be negatively affected when mares fed inadequate protein during late gestation, even when mares were maintained in a fleshy condition. It is not uncommon to see fat mares have small, weak foals when the mare’s diet was adequate in calories but low in quality protein. Even when mares are fed high protein forage, like alfalfa, the diet can be deficient in important amino acids and other nutrients. Late gestation mares should be fed a grain mix or supplement containing quality protein sources that will meet amino acid requirements fo r optimal foal development.

During the tenth month of gestation the greatest amount of mineral retention occurs in the unborn foal. Mare’s milk is practically devoid of trace minerals that are essential for proper bone development, such as copper. Forages, including pasture and hay are also low in trace minerals. Therefore, adequate trace mineral supplementation of the mare is critical for normal fetal development. Feeding a ration with the proper trace mineral balance during late gestation will meet the mare’s requirements and provide sufficient minerals for the developing foal. In the first weeks of life, foals will not eat sufficient amounts of fortified feeds and may not have adequate absorption of dietary trace mineral sources at this early stage of development. Proper mineral nutrition of the mare in late gestation helps insure that the developing foal will actually store a supply of these important nutrients for use after he is born. This will bridge the time from birth until foals are old enough to consume and assimilate these important nutrients from a well-balanced foal feed.

If a mare is thin during late gestation, meaning her ribs can be seen, this is the best time to provide enough calories in her diet to facilitate weight gain. It is nearly impossible to put weight on a lactating mare, and thinner mares, especially those nursing a foal, are less likely to become pregnant when rebred. This means that late gestation is the last chance to get a thin mare in good shape. In these situations, select a feed that is very calorie and nutrient dense, in order to supply the needed energy and nutrients to support weight gain without having to feed excessive amounts of grain.

While research has shown that fat mares don’t have a higher incidence of foaling difficulties, they may have a reduction in milk production which can negatively impact foal growth. If a mare is significantly overweight during late gestation, where ribs cannot be seen and are difficult to feel, you must provide adequate protein, vitamins and minerals to support optimal fetal development without adding unnecessary calories. In these cases, choose a concentrated protein, vitamin, mineral supplement that is designed to be fed at 1 – 2 lbs per day. This type of supplement will meet the nutrient needs of the foal without causing weight gain in the mare. It may be necessary to restrict hay intake to 1.5 lbs of hay per 100 lbs of body weight in significantly overweight mares in order to facilitate weight loss.

Proper nutritional management of the broodmare during late gestation will give her foal the best start in life. With all the time and money invested in getting a mare in foal and all the promise and potential that comes with a newborn foal, you don’t want to skimp on mare nutrition during this critical time.

Karen E. Davison, Ph.D. – Manager-Equine Technical Services Land O’Lakes Purina Feed