Horse Breeders Can Balance Mare Nutrition with New Guide

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Peggy Auwerda
Equine Specialist
Iowa State University Extension and Outreach

A new publication from Iowa State University Extension and Outreach helps horse breeders determine the dietary needs of their mares during gestation and lactation.

A mare’s gestation or pregnancy is approximately 340 days, or 11 months, according to Peggy Auwerda, associate professor in animal science and extension equine specialist at Iowa State University. The dietary needs change significantly during gestation and lactation, and are critical to the health of the horse and its foal. Mare and foal.

“Special attention must be given to the diet of the pregnant mare from conception to foaling,” said Auwerda. “This publication provides some background and definition as to what the gestating and lactating mare needs, and illustrates it with both tables and figures.”

According to Auwerda, the foal does not gain much weight during the first eight months of pregnancy, but growth becomes rapid during the second half, when the foal typically gains 75% of its final birth weight.

During lactation, the foal relies on the mare’s milk and may gain as much as two to five pounds per day. Energy in the feed, plus amino acids and protein, and nutrients like calcium and phosphorus must be sufficient to support the production of quality milk and maintain the mare’s body condition score.

The body condition is important to the overall health of the mare and its ability to re-breed. When the body condition score falls, it can take two months or more to increase. A chart within the publication shows the additional grain and time needed to increase the score.

Increasing the weight of a lactating mare is difficult, because so much of her energy goes into milk production. Also, one must be careful to avoid overfeeding the horse, which can cause colic and digestive issues.

Auwerda said the information in the publication, "Nutrition for the Gestating and Lactating Mare," applies to anyone involved with the breeding of mares – whether at the hobby or commercial levels.

For more information, Auwerda can be reached at 515-294-5260 or

Date of Publication: 
January, 2022