Winter, with its sometimes extreme weather, poses some nutritional challenges for pregnant mares because this is the transition time from mid to late gestation.
During the first seven or eight months of gestation, the fetus grows very slowly (approximately 0.2 lbs per day) so early pregnancy does not present much of a nutritional challenge to the mare. Dry mares in early gestation can basically be fed like any other mature, idle horse. Good quality pasture or hay along with a supplement such as Purina Free Balance 12:12 vitamin/mineral supplement or Enrich Plus Ration Balancing horse feed may be all that is necessary to meet these mares’ nutritional requirements.
However, during the last three–four months of pregnancy, the unborn foal begins to grow and develop more rapidly. During the last 90 days of pregnancy, the fetus gains approximately 1 lb per day. This has a significant impact on the mare’s nutritional requirements for protein, vitamins, and minerals. The increased size of the fetus also takes up more room in the mare’s body cavity, resulting in the mare eating less hay or forage. This reduction in forage intake, coupled with the increased nutritional demands of the pregnancy, leads to a need for mares to be supplemented with a nutritionally balanced concentrated grain mix to meet total nutrient requirements. 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 the body condition of the mare, other nutrients such as protein, vitamins, and minerals, will be deficient.
Just because a mare is in good body condition and carrying adequate body fat does not guarantee proper foal development. Research has shown that foal birth weight can be negatively affected when mares are not fed adequate protein during late gestation, even when the mares are maintained in a fleshy condition. It is not uncommon to see fat mares have small, weak foals when the mares’ diets are adequate in calories but low in quality protein sources. Even when mares are fed high protein forage, such as alfalfa, the diet can be deficient in important amino acids. Research has shown that even high-quality alfalfa is not well digested in the horse’s upper gut, thus some of the essential amino acids are not available to the animal to meet requirements. Mares in late gestation should be fed a grain mix or supplement containing quality protein sources that will help meet amino acid requirements for 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. Therefore, adequate trace mineral supplementation of the mare is critical for normal fetal development and provides sufficient minerals for the developing foal to store in its body to utilize immediately after birth. 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 ensure that the foal receives an adequate supply of these important nutrients to use during very early growth stages. Pastures and hays are usually quite deficient in trace minerals such as copper and zinc, so sufficient mineral supplementation in the mare’s total diet is critical. All of the aforementioned Purina premium feeds are designed to provide adequate minerals to meet the needs of the mare and unborn foal when fed as recommended.
If a mare is thin during late gestation, meaning that her ribs can be seen, it is important to feed enough calories so that she gains weight, especially if she is to be bred again. It is very difficult to put weight on a lactating mare, and thinner mares, especially those nursing a foal, are less likely to get back in foal. Plus, lactating mares need a great deal of energy to support optimal milk production. This means that late gestation is the last good opportunity to get a thin mare in good shape for supplying milk for the suckling foal, as well as preparing for the next breeding season. In these situations, select a feed that is calorie and nutrient-dense, such as Purina Omolene #200, Strategy GX, or Ultium Growth horse feed, in order to supply the needed energy and nutrients to support weight gain without having to feed excessive amounts of grain.
While research found that fat mares had a higher incidence of foaling difficulties than thinner mares, obese mares did have a reduction in milk production. If a mare is significantly overweight during late gestation, where ribs cannot be seen and are difficult to feel, it is important to provide adequate protein, vitamins, and minerals to support optimal fetal development without adding unnecessary calories. In these cases, choose a concentrated protein, vitamin, or mineral supplement that is designed to be fed at one to two pounds per day, such as Purina Enrich Plus Ration Balancing horse feed. This type of supplement will meet the nutrient needs of the unborn foal without causing weight gain in the mare. It may be necessary to restrict hay intake to 1.5% of the mare’s body weight if she is significantly overweight.
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 foal on the ground, you don’t want to skimp on mare nutrition during this critical time.
Source: Karen Davison, Purina Animal Nutrition, Ph.D.