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Copyright 2010 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor;


Feeding Broodmares  

through Pregnancy, Parturition & Rebreeding

by Heather Smith Thomas, Salmon, ID


April 2010 Issue


     The traditional rule of thumb in feeding broodmares is that, energy-wise, the requirements in early pregnancy are not much different from the energy requirements for body maintenance. The pregnant mare’s greatest requirements are during the last trimester of gestation when the fetus is growing the fastest.

     Brian Nielsen, PhD, PAS, Dpl. ACAN (Diplomat of American College of Animal Nutrition) Professor, Department of Animal Science at Michigan State University , says that this is still an appropriate guideline, but mare owners should make sure the mare is in adequate body condition.

     “People used to think mares should be thin rather than fat,” says Nielsen, “and this is still the mind-set, for some people. I took a mare to a farm to be bred this year, and she’s a bit on the chubby side, and the farm manager said his vet wouldn’t like to see that; his vet likes the mares thin.”

     “But the data is clear on this, when you look at the research,” he continues. Fleshy mares do better reproduction-wise, than thin ones.

     “A few days after I took the mare to the farm, the manager called me back and said she was bred. She settled and was in foal, and that’s the way it’s supposed to be.

     “If a mare is thin, however, you can end up with problems. It takes longer to get a thin mare in foal. If you are rebreeding her after foaling, it takes her longer to start cycling again if she’s thin,” he explains. Mother Nature considers reproduction a luxury and takes care of that department only after all the other needs of the mare are met.

     “It’s also harder to keep her pregnant once she is bred. You definitely want mares to be at a body score condition of 5 or higher, on the scale of 1 to 9 (1 being emaciated and 9 being obese). Any time you begin to see some ribs, this creates some issues for reproduction,” says Nielsen.

     “Even if the mare is at body condition 5 when she foals, where you can’t see the ribs but can easily feel them, the problem is that her energy demands for lactation are so great that pretty soon she’ll lose a little weight.

     “There’s an old saying that you should ‘feed a mare like a dairy cow or else she’ll look like one.’ The problem with a broodmare is that she’s getting thin right at the time you want to rebreed her.”

     Her demands for producing milk are going up and she may rob some of her body reserves to meet that demand. It’s not impossible, but it’s very difficult to meet her energy requirements through diet alone when the mare is lactating in the early stages, so it’s best to have some body reserves.

     In earlier years, many people were concerned about mares being fat at the time of foaling, thinking they might have more foaling problems or problems with milk production, since this can be true with cattle. An obese cow has increased risk for dystocia (difficult labor or delivery), since she has more fat in the pelvic area, and may also tire more readily during labor.

     Mares are a different story however. “There have been studies in which mares were at a body condition score of 8 or 9 at foaling time—very obese—and this did not increase the problems with dystocia.”

     This may be partly due to the fact that a mare does not take nearly as much time in active labor as the cow. It is normal for a cow to be in second-stage labor for 30 minutes to an hour or longer, with little risk to the calf even if she’s in hard labor for 2 or 3 hours. In this situation, however, a fat cow will tire more readily and if she quits pushing because she’s exhausted, the calf is certainly at risk.

     In contrast, a mare is in active labor for a much shorter time, and there’s less endurance needed. A fat mare will generally have her foal before she becomes tired.

     “A chubby mare is not a bad thing,” says Nielsen, “though you don’t want her to be obese because that can cause some potential health issues. You absolutely do not want her thin, however. So when we’re looking at broodmare nutrition, to me, this is the biggest issue—convincing folks that it’s a good idea to have a little body reserve on the mare. Beyond that, it’s just a matter of a little fine-tuning on her nutrition.”

     The nutritional requirements for the broodmare in early stages of pregnancy are not dramatically different than for horses at maintenance, except that some of these mares are lactating.

     “By the time she gets out to the ninth or tenth month of gestation, however, there is certainly an increase in energy requirements, over body maintenance, and some of the mineral requirements go up a little. This is where it becomes a bigger issue, but these requirements can generally be met with good feed. A fair amount of mineral is being deposited in the young fetus.

     “People who are feeding straight grain such as oats, and some type of hay that’s low in calcium could create a problem with too much phosphorus and not enough calcium for ideal bone deposition. If you are feeding commercial concentrate or a legume hay, you are probably fine, however. Some of the grass hays that are a little lower in calcium, fed with straight oats or straight corn might create an inverted calcium/phosphorus ratio, which could cause problems,” he says.

     If you’re going to feed grains or a grain mix, he recommends using a commercial concentrate that’s already balanced for minerals. “Copper is one that people tend to be concerned about. There have been thoughts that low copper concentrations in diet may be linked to osteochondrosis (defective development of the bone).

     “But when people started worrying about this 20 years ago and started adding a lot more copper to commercial concentrates, this didn’t halt the problem; we are still having osteochondrosis,” says Nielsen. It may play a role, but it’s definitely not the biggest factor.

     “About the only place that I’d say you need to worry about copper levels in the mare’s diet is if you have really low amounts, such as less than 10 or 12 parts per million,” he says. In those instances if you are just feeding hay or grain grown in copper-deficient soil, you could have problems, and it’s better to feed a commercial grain mix that has copper added.

     Selenium is another item in the diet that is adequately supplied by feeds grown in normal soils, but may be deficient in some regions. Talk to your county Extension agent or veterinarian to know if this element should be supplemented if you are feeding locally grown hay and/or grain.

     “Here in Michigan ,” says Nielsen, “we are selenium deficient, but if we feed commercial concentrates, most of those have the maximum amount of selenium that can be added. In fact, some people can get into trouble feeding several different supplements because the horses may be getting too much selenium.

     “This is actually one of my biggest concerns, that horse owners over-supplement. Usually just a good forage and a good concentrate will be adequate, and you are totally covered for selenium. The vast majority of commercial feeds and supplements contain adequate amounts,” he says.

     Protein requirements for the mare will increase a little in later stages of gestation, but this, too will be adequately covered with a commercial grain mix and/or legume hay.

     Feeding the lactating mare is a little different, in that her requirements will be higher, producing milk as well as growing the fetus.

     “Normally the main concern for a mare is for lactating, versus pregnancy, since lactation creates more demand for protein, energy, etc. During the first four months of gestation we are not so much concerned about providing extra nutrients for pregnancy, but more concerned about nutrients because she’s lactating.”

     Most people will be weaning the foal by the time the mare reaches late gestation, and she won’t be lactating at that crucial time of fast growth for the fetus.

Heather Smith Thomas is the author of numerous articles and 20 books. She and her husband ranch near Salmon, Idaho . For more information about her books, visit

     Heather’s blog online is:


Copyright 2010 Rocky Mountain Rider. ALL RIGHTS RESERVED. Reproduction of any editorial material, artwork and photos is strictly forbidden without express written permission of the publisher. For information about reprint rights, please contact the editor;


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