Q: My pregnant mare tends to be a bit of an “air fern.” We’ve done a good job keeping her at a reasonable weight for most of her pregnancy, but I know her nutritional needs will increase in her final months of gestation. I’m not sure how to strike that balance between getting her the nutrients she needs while not letting her get too heavy. I worry about how her weight might impact the foaling process, not to mention obesity putting her at greater risk of laminitis. Do you have any tips to help?

A: What a great question, and I’m sure you’re not the only one trying to balance healthy body condition with adequate nutrition for a late gestation mare. Providing appropriate nutrition to pregnant mares is critical to the proper development of the foals they’re carrying, but that can be challenging when a mare is an easy keeper tending toward obesity. 

First, work with your veterinarian to ensure the overall health of your pregnant mare. Second, use the Henneke body condition scoring system to evaluate her body condition score (BCS). Pregnant mares should maintain a body condition score of 5.5-6.5 on the Henneke scale. This range ensures your mare has a little extra condition to support her through foaling and early lactation without approaching obesity and increasing the risk of metabolic issues. 

Nutritional Guidelines for Pregnant Mares

During the first seven or eight months of gestation, the fetus grows very slowly (approximately 0.2 pounds per day), so early pregnancy does not present a significant nutritional challenge to the mare. You can feed dry mares (mares without foals at their sides) in early gestation like any mature horse at maintenance. Good-quality pasture or hay, along with free-choice salt and a daily ration balancer, might be all that is necessary to meet the nutritional requirements of mares in early gestation. During the last three or four months of pregnancy the unborn foal begins to grow and develop more rapidly. The fetus gains approximately 1 lb per day over the last 90 days of gestation. This has an 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, which could cause the mare to eat less hay or forage. To ensure your late-gestation mare receives proper nutrition and additional calories, offer her a well-balanced mare and foal feed.  

Protein, Minerals, and Body Condition Management

In some cases, when gestating mares consume plenty of high-quality forage, owners might reduce or eliminate supplemental feed to restrict calorie intake. This practice often results in an overweight mare and a growing foal missing out on important nutrition. Researchers have shown that foal birth weight can be lower than normal when mares do not receive adequate protein during late gestation, even when they maintain a fleshy condition. Mares fed high-protein forage, such as alfalfa, can still have a diet deficient in important amino acids. 

In addition, significant mineral retention occurs in the unborn foal during the 10^th month of gestation. A mare’s milk is practically devoid of trace minerals essential for proper bone development. In the first weeks of life, foals will not eat enough fortified feed and might not adequately absorb dietary trace mineral sources at this early stage of development. Pastures and hays are usually quite deficient in trace minerals, so your mare will need additional mineral supplementation in late-gestation for normal fetal development and for the developing foal to store in his body and draw from after being born. 

Researchers have indicated that overweight mares don’t have a higher incidence of foaling difficulties, but obese mares do have lower milk production, which will negatively affect early growth of their foals. Late-gestation mares with a body condition score of 7 or greater must consume adequate protein, vitamins and minerals to support optimal fetal development. A ration balancer provides concentrated nutrition in a 1–2 lb feeding rate that will meet the nutrient needs of the unboarn foal without adding unnecessary calories to cause weight gain in the mare. You might need to restrict hay consumption to 1.5% of the mare’s body weight to further control calorie intake if the pregnant mare maintains a higher BCS.

Take-Home Message

Proper nutritional management of the broodmare during late gestation will give her foal the best start in life. With everything it takes to get a healthy foal on the ground, you want to make sure they’re both well supported through this critical time.

Do you have an equine nutrition question?