Feeding Pregnant Broodmares

March 20, 2025

The goal of any equine breeding program is to produce strong, sound foals. To do this, there are several factors involved including genetics, environment and nutrition. Nutrition is a critical piece of any successful breeding operation. Mare owners spend thousands of dollars on stud fees and shell out hundreds of dollars in veterinary care to prepare their broodmares for breeding and foaling. Mares are expected to grow a healthy foal inside them for 11 months and produce enough milk for that foal for up to 6 months. Furthermore, many mares are expected to raise healthy foals year after year, requiring successful rebreeding while the previous year’s foal is still by her side.

Because nutrition influences each stage of the broodmares production cycle, nutritional management may, in many ways, determine the success of the breeding program. Nutrition for the pregnant mare can be broken down into several different stages: conception, early, mid and late gestation.

Breeding and Conception in Broodmares

The effect of nutrition and body condition on reproduction in mares has been clearly illustrated. Broodmares coming into the breeding season with an optimal body condition score (5-7) start cycling earlier than those with a low body condition (less than 5). Thinner mares also have difficulty conceiving and maintaining pregnancy as compared to mares in optimal body condition. Some obese mares continue to cycle throughout the winter when typically, reproductive cycling is shut down. Obesity has been associated in horses and ponies with decreased insulin sensitivity, and both obesity and decreased insulin sensitivity have been associated with decreased reproductive function in mares.

Feeding Broodmares for Breeding

Broodmares in optimal body condition going into the breeding season typically do well on good quality forage and a concentrated vitamin and mineral pellet (balancer pellet). If mares are overweight prior to the breeding season the combination of vitamin and mineral pellet and exercise is an ideal program to get them into optimal shape before breeding. If the mare is underweight high-quality hay, including alfalfa, and potentially a fortified grain concentrate may be necessary to help increase the mares’ body condition in preparation for breeding.

Early and Mid-Gestation for Broodmares

From the time of conception through foaling, the fetus is actively growing. However, fetal growth is not occurring at a steady rate. Fetal growth is quite slow during the first seven months of pregnancy and then very rapid the final trimester. During early and mid-pregnancy, the developing fetus is very small, less than 20% of birth weight. This represents less than 2% of the mare’s body weight.

Feeding During Early and Mid-Gestation

The nutrient requirements of the mare during early pregnancy are very similar to the nutrient requirements of a non-pregnant mare. A common feeding mistake is to over feed mare’s calories during early pregnancy causing them to become overweight. An all forage (hay or pasture) diet fed at a rate of 2 to 2.5% of body weight will provide most mares with adequate levels of both energy (calories) and protein but is likely deficient in several key minerals. Feeding a “balancer pellet – protein/vitamin/mineral pellet” during early and mid-pregnancy along with good quality forage, such as timothy or orchard grass hay, will ensure the adequate levels of micro and macro minerals along with critical vitamins and being met in the diet.

As a word of caution, not all hay/pasture is suitable for pregnant mares. Endophyte infected tall fescue hay/pasture should be avoided since it has known negative effects on pregnancy, lactation and the delivery of a live foal.

Late Gestation Nutrient Requirement Changes in Broodmares

During late pregnancy, the fetus will gain approximately 80% of its birth weight. To support this rapid fetal growth, the mare’s requirements for energy, protein, minerals and vitamins increase. For example, an 1,100 lb mare increases her protein requirement from 630 g per day pre-pregnancy to 893 g per day in the 11th month of pregnancy. Digestible energy (calorie) requirements increase from 16.7 Mcal/day pre-pregnancy to 21.4 Mcal/day during the 11th month of pregnancy for the same mare (NRC, 2007). This equates to approximately a 41% increase in protein requirement and a 28% increase in calorie requirements. Similarly, the requirements for minerals that are in highest prevalence in bone (calcium and phosphorus) also increase. The calcium requirement for a mare prior to pregnancy is 20 g per day, but increases by 80% in the 11th month of pregnancy to 36 g per day. Phosphorus requirements increase by 87% from 14 g per day prior to pregnancy to 26.3 g per day during late pregnancy. That data is represented in the table below (NRC, 2007).

How a Mares’ Nutrition Impacts the Foal

The requirements for trace minerals are especially critical since the mare will fortify the unborn foal liver with minerals such as copper, zinc and selenium. Mare’s milk is not a good source of these trace minerals therefore they must be stored in the foal’s liver prior to birth. The foal utilizes these minerals during the first two months of life to support proper skeletal growth. Without proper liver stores of trace minerals, the foal may be predisposed to growth disorders.

Feeding During Late Gestation

Compounded with an increased requirement for nutrients, the mare in late pregnancy has a limited capacity for feed intake due to the size of the fetus compressing the digestive system. To meet the nutrient needs of mares in late pregnancy, voluntary consumption of hay intake is often reduced to 1.5 to 2% of body weight and fortified grain is fed as a concentrated source of essential nutrients. High quality hay including alfalfa is often fed to boost nutrient contribution by forage. A fortified grain concentrate, designed for a pregnant mare, that contains quality protein and bioavailable sources of minerals to ensure enhanced uptake and absorption is the correct choice.

Water Requirements for Pregnant Broodmares

Water intake is a critical component of a pregnant mare’s diet, particularly in late gestation when her requirements increase to support both her own physiological needs and the developing fetus. A general guideline is that horses require approximately 1 gallon of water per 100 pounds of body weight daily. For a 1,000lb broodmare, this means a baseline requirement of 10 gallons per day, with an additional 5 gallons often needed to support fetal growth. When mares are consuming predominantly dry feedstuffs, such as hay and grain, rather than moisture-rich pasture, adequate water intake becomes even more essential to maintain proper digestion and reduce the risk of impaction colic during pregnancy.

Key Takeaways for Feeding Pregnant Broodmares

Preparing a mare for breeding and properly feeding her through conception, early pregnancy and late pregnancy is critical to producing a healthy foal.

• Broodmare diets should concentrate on optimizing body condition, while providing optimal levels of protein, vitamins and minerals
• Diets should always be based on high-quality forage (2 – 2.5% of body weight)
• Additionally, either balancer pellets or grain concentrates designed for a pregnant mare should be fed to provide essential nutrients that may be lacking in the forage portion of the diet

If you have questions, please contact the nutritionists at Standlee, or consult with your veterinarian.

By Dr. Stephen Duren
Standlee Nutritional Expert - Performance Horse Nutrition