Mares represent the mainstay of any commercial or private breeding enterprise. In addition to their all important genetic contributions, mares provide a protective and nourishing environment in which to raise their foals, both before and after birth. Without a doubt, the nutritional status of mares is a critical component in foal health from the moment of conception and continues through weaning.

The publication of the National Research Council’s latest revision of Nutrient Requirements of Horses offered up several new thoughts on broodmare nutrition in the two most important phases of production, gestation and lactation.

Prior to the publication of the most recent version of Nutrient Requirements of Horses, industry professionals divided a mare’s gestation into two distinct nutritional periods:

(1) from the time a mare was pronounced in foal to about eight months (early gestation; first and second trimesters), and

(2) nine months to approximately eleven months or birth (late gestation; third trimester).

In previous editions of Nutrient Requirements of Horses, dietary requirements for mares in the first and second trimesters were similar to any mature horse at maintenance. Moreover, because it is a well-known fact that foetal growth is most rapid during the last trimester, an increase in certain nutrients such as energy and protein was recommended during the last three months of pregnancy.

Recent research has indicated, however, that the provision of certain vital nutrients should be increased long before the nine-month mark. As previously, mares should be nourished the same as any horse at maintenance for the first four months of gestation, but recommendations now suggest that every subsequent month represents a separate period, leading to eight distinct periods.

The research that brought about these changes takes into account not only maintenance of the mare’s body weight and foetal growth, but also the nutritional expenditures involved in the creation and maintenance of less obvious gestational tissues such as the placenta and mammary glands. Collectively, these are called non-foetal tissues.

With no changes made to nutritional requirements in early gestation (0-4 months) or late gestation (9-11 months), Nutrient Requirements of Horses suggests nutritional changes primarily for mares during mid-gestation, the period between the fifth and eighth months of pregnancy.

What nutrients are affected?
To support development and maintenance of non-foetal tissues, Nutrient Requirements of Horses recommends that protein and energy requirements be raised 5 to 8 percent above maintenance during mid-gestation for an average (500-kg) mare (see Table 1 below).

Unlike protein and energy, the requirement for additional minerals seems to appear later in the gestation, at approximately seven months. This can be attributed to the fact that non-foetal tissues require mostly protein and energy and very few minerals for accretion and subsequent maintenance.

Nutritional requirements for lactation have historically been based on the combination of two specific values: the requirements necessary to keep the mare in optimal body condition and the nutrients required for high quality milk production (volume and nutritional composition).

Traditionally, nutrient requirements were thought to be much greater in associated with protecting and tending to a foal and the increased energy needed by the gastrointestinal tract to digest the larger meals required to support lactation.

Feeding the mare during gestation and Lactation

The mare’s feeding program should be adjusted to accommodate the differences in requirements throughout gestation and lactation. An increasingly popular method is based around a two-step feeding concept that includes the use of both a balancer and a fully fortified feed (textured or pelleted). A balancer is a low-intake, concentrated source of essential protein, vitamins, and minerals, which is designed for all classes of horses when additional calories are not required.

Balancers can be fed alone to mature horses that are maintained on all-forage diets, or can be added to mixes when extra nutritional fortification is required. Balancers can also be fed with unfortified grains to provide the correct balance of nutrients. Barren mares and those out on grass that tend towards the heavier side benefit from being fed a balancer, which when fed at the recommended daily intake (usually approximately 1 kg per day depending on the specific product) provides a base nutrient package during all phases of the breeding cycle.

When additional energy is needed, a fully fortified feed can be used. These feeds contain not only the protein, vitamins, and minerals required for the animal, but also the energy. A fully fortified feed is usually fed at a higher intake than a balancer (approximately 4-5 kg vs. 1 kg per day). The balancer and complete feed must be coupled with a good-quality forage source, such as hay, haylage, and/or pasture fed at 1-1.5% of body weight per day.

For mares that do not require such a high intake of a fortified feed, but cannot maintain their weight on a balancer alone, many farms opt to implement a two-part feeding system of using a balancer with a fortified feed at various intakes and adjusting energy levels as required during the breeding season. Feed intakes will vary, depending on stage of gestation and lactation, and the changing needs of the individual, but the two-step system is designed to maintain a constant base nutrient intake, while adjusting energy.

The modifications and increased nutrient requirements for broodmares during gestation and lactation that appear in the revised National Research Council recommendations do not necessarily change the foundation of a broodmare’s feeding program, especially when using the two-step system and ensuring the mare is maintained on an appropriate base nutrient package throughout all phases of reproduction. As it is predominantly energy requirements that have been revised by the National Research Council for gestation and lactation, it is now, more than ever, imperative to feed each mare as an individual. It is vital to regularly assess body condition score throughout all phases of reproduction and modify caloric intake as necessary.

For more information on feeding the broodmare during the important stages of the breeding season, or any other aspect of equine nutrition, please contact Kentucky Equine Research at

This article is reprinted with the permission of Kentucky Equine Research.

For further information and nutrition advice, please contact KER on 1800 772 198, or

Researchers ramp up nutritional requirements of Broodmares
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