12/11/2015 4:50PM

Horse health: Broodmares need special diets

Courtesy of Juddmonte Farm
Broodmares need special nutrition to ensure their health and that of their foals.

By Denise Steffanus

Every broodmare owner has heard the mantra about increasing calories to keep the mare in optimum body condition score for conception, support her and her fetus during gestation, and enable her to provide ample milk for her foal. But broodmare nutrition is more complex than simply increasing rations. How you reach that optimum body condition score of six on the nine-point Henneke scale is important.

Body condition score six is described as “moderately fleshy.” The mare may have a slight crease down her back. Fat over her ribs feels fleshy-spongy, and fat around her tailhead feels soft. At score six, fat also begins to be deposited along the sides of her withers, behind her shoulder, and along the side of her neck.

“I can take whole oats and dump oil on the feed, and I can probably get a fat mare out of that diet, but I have a fat mare that probably doesn’t have enough calcium, phosphorus, copper, zinc, and manganese,” said Josie Coverdale, Ph.D., associate professor of equine nutrition and management at Texas A&M University.

Coverdale said to keep in mind that the diet you feed your broodmare has to both maintain that mare and build a foal. Any essential nutrient that is missing in the mare’s diet will cause the fetus to draw it from the mare’s body, to her detriment. For a mare that is bred every year, this can have a cumulative effect because she never has the opportunity to recover between pregnancies.

Broodmare-specific diet

Merely feeding a broodmare more of the same diet you feed other classes of horses on the farm is not appropriate, because her requirements are different.

“What we look at in horse diets is not just minimum requirements but the relationships between all those nutrients, and the most important relationship is the one of a nutrient to a single calorie,” Coverdale said. “In a maintenance horse diet for your typical pasture ornament, you have a fairly low nutrient input for every calorie in the diet. With a racehorse, you have a fairly high calorie input, but, quite frankly, not a huge increase in the nutrients. But for a broodmare, you get both the high calorie need and the high nutrient need, so those diets have to be specially formulated.”

In formulating a proper diet, Coverdale emphasized the need to submit pasture and hay samples, as well as samples from natural water sources – ponds, streams, and deep wells – to the local extension service for analysis. Without these test results, knowing what nutrients a mare is consuming is a guessing game.

It is important to know the mineral content of natural water sources and the possible presence of contamination from runoff. High levels of magnesium in water could interfere with calcium, and water with high iron content could bind copper in the mare’s diet, creating a copper deficiency. Copper is needed for proper cartilage and bone development of the fetus, and it aids the ability of the mare’s arteries to expand and contract without tearing. Farms where rupture of the uterine artery in aged broodmares is a recurrent problem need to pay particular attention to copper levels.

Nutrient content of pasture changes with the seasons and environmental conditions. If pasture is the main source of forage throughout the mare’s pregnancy, periodic assays are essential. Most local feed mills have an in-house nutritionist who is familiar with local conditions, such as the selenium and copper status of the region’s forage, and what nutrients are needed in a broodmare feed to compensate for those conditions.

If the hay you buy is shipped from another area, it may have a different composition from local hay, so switching from one batch of hay to another could warrant a change in diet to compensate for those differences.

With the results of the forage and water tests in hand, you can consult a nutritionist to determine which commercial feed will best round out the mare’s diet to provide a balanced ration.         

Coverdale does not recommend one commercial broodmare feed over others or national brands over those formulated by local feed mills, as long as a knowledgeable equine nutritionist is formulating the broodmare feed.

Also keep in mind that the mare’s nutritional needs will change from trimester to trimester. For the first trimester, nutrients are important for maintaining the pregnancy, and if the broodmare is rebred while she is still nursing this year’s foal, she will need heightened nutrition during the first trimester to nourish the fetus that will be next year’s foal. During the second trimester, minerals are important for the fetus to build cartilage into rigid bones. In the third trimester, nutrients must support the rapid growth of the fetus and prepare for lactation and rebreeding.     

Essential nutrients

In the fetus, bones first form as cartilage and then turn into bone. Not only are calcium and phosphorus essential for this process, but they must be provided in the proper balance. The total calcium-to-phosphorus ratio in the mare’s diet should range from 1.5:1 to 2:1.

“On a high-grain diet, it’s very easy to have improper ratios of calcium and phosphorus,” Coverdale said. “We have a lot of owners who are still feeding whole oats, and they might be meeting the energy need of that mare, but her calcium:phosphorus ratio is inverted.”

It is easy to recognize when a mare pulls fat stores from her own body to nourish her fetus, but when she is forced to dip into her body to provide her fetus with essential amino acids, the building blocks of muscle, it is less obvious because it affects her lean muscle mass.

“That foal in utero, especially during that last trimester, is really rapidly growing, and it requires really high-quality nutrients,” Coverdale said. “That’s where essential amino acids become important, calcium and phosphorus become important, and trace minerals that are involved in joint development, such as copper and zinc and manganese, become important.”

Lysine typically is the first essential amino acid to become deficient. The most plentiful source of lysine in a horse’s diet is soybean meal, which most feed manufacturers use as the principal source of protein.

Vitamins A and E are important for conception. Beta-carotene, the source of Vitamin A, is used by the ovary in the production of the corpus luteum, which secretes progesterone. Progesterone, in turn, controls ovulation, embryo implantation, and pregnancy maintenance. Vitamin A also serves as an antioxidant. Vitamin E also is a powerful antioxidant that helps to protect against tissue damage.

Selenium and vitamin E go hand in hand. They function jointly to protect body tissues from oxidative damage by free radicals. When mares are selenium deficient, they can have foals that are born with a type of muscle dystrophy called white muscle disease. This most often is seen in broodmares that are not fed a commercial grain ration but subsist solely on pasture that has a low selenium content. However, it is important to verify the deficiency before adding selenium to the diet because of the danger of selenium toxicity.

Because fat-soluble vitamins A, D, E, and K are stored in the mare’s fat cells, Coverdale cautioned that supplementing a broodmare’s diet with them when no deficiency is present could lead to toxic levels. For example, in other species, including humans, toxic levels of vitamin A in early pregnancy have been linked to birth defects.

“There isn’t one single nutrient that a fetus demands that’s way more important than another,” Coverdale said. “It’s all about balance, and this is where I think people get confused. They read an article that says, ‘Vitamin A is important during late pregnancy,’ and they start supplementing it. Yes, it is, but so is lysine, calcium, phosphorus, copper... I could basically create a laundry list of things that are important, meaning greater concentration is required during late pregnancy.”

She warned owners not to single out certain nutrients to supplement in the mare’s diet without an analysis that indicates a deficiency exists and the advice of an equine nutritionist.

Coverdale said the window of opportunity to make needed changes in the broodmare’s diet depends on when a problem is recognized.

“If you catch it really early in pregnancy, you have a huge window of opportunity to make a difference,” she said. “If you catch it during that third trimester, when fetal growth really takes off and gets aggressive, it becomes harder to fix that inadequacy. The closer you get to parturition, the more difficult it will be to make a difference. Because once you start lactation, it’s not impossible but it’s very difficult to put weight back on a mare, regain body condition score, and reestablish ideal weight for that mare once she starts that lactation process.”

The future athlete

Coverdale and her colleagues are investigating whether it is possible to program during gestation how that foal will utilize fuel (glucose and insulin) as an adult athletic horse.

“Our next step, within the next year, is to do some more work to actually look at what happens in the foal’s pancreas during development,” she said. “Are we actually altering that organ and its function? I think if we can figure out what we are modifying in the pancreas itself, then we can start tracking those changes in older horses.”

Imbalances and deficiencies that affect the foal in utero also could predispose it to developmental orthopedic disease (DOD) that affects its athletic performance. Developmental orthopedic disease includes epiphysitis, degenerative joint disease, and osteochondritis dissecans (OCD).

“If you look at DODs in general, there isn’t any reason to think that process of predisposition doesn’t start in utero,” Coverdale said. “That’s a foal’s first exposure to nutrients, and if those nutrients are imbalanced or deficient, then it is not an unreal possibility that that’s a starting point to increase your odds of those problems. Do I think there’s one thing I can feed a horse to fix that? Honestly, no.”

Coverdale’s advice to broodmare owners: “Buy as high-quality forage as you can and have it tested so that you know what you’ve got, and then choose an appropriate commercial ration that best matches that forage. That’s what most people can do to be pretty simple and pretty successful.”