Once your mare is pregnant, consider her nutritional requirements in three stages. The first stage is the first two-thirds of her pregnancy. During this time, the fetal size does not increase significantly and your mare should still be on a maintenance diet. Her body condition should stay constant, again without losing or becoming obese. A mare that is losing weight will have a hard time re-breeding, and an obese mare will have more trouble foaling due to weak muscles and condition. If necessary, this stage of pregnancy is the best time to adjust body condition because they can increase energy stores while nutrient demands are relatively low.
The second stage of your mare’s pregnancy is the last three months. In this time, the fetus increases about one pound per day, accounting for two-thirds of fecal growth. Energy, protein, calcium, and phosphorous requirements increase. When your mare is on a maintenance diet, good hays and grasses or legumes will usually be enough. Once into her last three months, it is a good idea to consider supplementing with concentrated feed sources.
The third stage of pregnancy is lactation. This stage requires by far the most nutrients and is a time of great physiological stress. The only other time that any horse’s nutritional requirements would be as high as during lactation is if they are in very intensive training. During this time your mare has to recover from the stress of parturition, produce milk, and often re-breed. All of her nutritional requirements will increase. During lactation, a healthy mare will produce 3% of her body weight in milk per day for the first three months, then 2% of her body weight in milk per day towards the end of lactation. If her nutritional needs are not met during lactation, her body condition will be affected the most. In extreme nutrient deficiency, milk production can decrease as well. As your mare’s milk production decreases, her feed intake should be adjusted as needed. At weaning, feed intake should be gradually decreased, allowing the mare to “dry up” faster and will prevent obesity. You should allow 7-10 days for mares to adjust to intake changes.
It is important to consult your veterinarian before any nutritional changes in your mare’s diet, and your veterinarian should be actively involved in your mare’s pregnancy. You can also contact your local Cooperative Extension office with any questions.
Gibbs, Pete G., and Karen E. Davison. “Nutritional Management of Pregnant and Lactating Mares.” Texas A&M University Department of Animal Science Equine Sciences Program. Web. 15 Feb. 2012. http://animalscience.tamu.edu/images/pdf/nutrition/nutriton-nutr-mgmt-pregnant-mares.pdf
“Nutrition of the Broodmare.” University of Kentucky Cooperative Extension Service. Web. 15 Feb. 2012. http://www.uky.edu/Ag/AnimalSciences/pubs/asc112.pdf.