Originally published on TheHorse.com
Editor's note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 Kentucky Equine Research Conference, held May 17-18 in Lexington, Ky.
Developing a feeding plan for a single horse takes careful consideration. But planning a feeding schedule for broodmares necessitates even more though, as these horses are often consuming nutrients for two.
During a presentation at the 2012 Kentucky Equine Research (KER) Conference, held Mat 17-18 in Lexington, Ky., Peter Huntington, BVSc (Hons), MACVSc, MRCVS, director of equine nutrition at KER Australia, discussed some keys to address to make when feeding and managing broodmares at all stages of pregnancy.
"The nutrition of the mare makes a different in the health, growth, and performance of her foal throughout its life," Huntington noted, as an adverse fetal environment caused by poor broodmare nutrition can cause reduced or abnormal fetal growth.
"Broodmares are often 'forgotten' until the third trimester or lactation, but they might be overfed in early pregnancy," he added, stressing the importance of a balanced broodmare diet throughout the year.
Huntington pointed out several areas in broodmare nutrition that need special attention.
Body Condition--When feeding broodmares, aim to keep them at a body condition score of 5 to 7 on a 9-point scale, Huntington said. Thin mares that have a body condition score of less than 5 tend to have longer gestation periods, longer time between estrus cycles, and lower pregnancy rates. Some very thin mares also have decreased milk production, he noted. The mares also tend to produce smaller foals, he said.
On the other hand, Huntington said a study carried our using two groups of pregnant mares--one group had healthy body weights while the other group of mares was considered fat--showed no difference in foaling or pregnancy rates, but the feed costs for the overweight mares were twice as high as costs associated with mares at a healthy weight. Additionally, overweight mares run the risk of laminitis development, he added.
Energy Balance--Most broodmares need balanced energy in their diets, Huntington said. A positive energy balance means the mare is gaining or maintaining weight, while a negative balance means she is losing weight, he said. Monitoring a mare's body condition and weight on a regular basis will help an owner determine if her energy requirements are being met.
Mares in up to four months of gestation have similar energy requirements to a horse consuming a maintenance diet, Huntington said. After that their energy needs will increase as the fetus begins to grow larger, he said, and when she begins lactating, her energy needs will nearly double compared to mid-pregnancy.
Ensuring a mare has access adequate energy source to meet her increased requirements will help ensure a healthy foal with a good start to life, Huntington said.
Protein--"Protein is one of the most important nutrients for a successful breeding program," Huntington said. Previous research has shown that a protein deficiency in broodmares can result in reduced reproductive efficiency, early embryonic death, and reduced foal size, he said. Additionally, mares will draw upon protein reserves in their bodies to "feed" their fetus and aid in milk production if appropriate dietary protein isn't provided.
Mares that are open, barren, and in early pregnancy have similar protein requirements to horses on a maintenance diet. Beginning around five months of gestation, the mare's protein requirement increases monthly through to foaling to account for fetal protein accumulation and then has a dramatic rise after foaling to supply protein lost in milk production.
Huntington discussed one study that showed supplementing a mare's diet with 500 grams of soybean meal (a quality source of protein) two weeks prior to foaling and 750 grams of soybean meal 7 weeks after foaling increased the mare's milk crude protein content and increased foal growth rate.
Minerals--During pregnancy and lactation, broodmares' calcium, phosphorus, and magnesium requirements increase as well, Huntington said. All three macrominerals are important to aid in fetal bone growth in late gestation, and for foal bone development prior to weaning, he noted.
The National Research Council (NRC) recommends increasing broodmares' calcium intake from 20 grams per day in early gestation to 28 grams per day at seven months of gestation, and again to 36 grams per day in the final three months of pregnancy. Huntington relayed that lactating mares have a calcium requirement three times greater than nonpregnant mares, so ensure broodmares consume enough calcium while lactating.
In a similar pattern to calcium requirement increases, broodmares' phosphorus needs increase during gestation and lactation. Huntington said that during the last three months of gestation, mares' phosphorus requirements double over early pregnancy, and mares then see a 50% increase in phosphorus requirements during early lactation.
Finally, magnesium requirements are also believed to increase during late gestation and early lactation. Huntington estimates mares should consume 10 to 12 grams per day during gestation and upwards of 15 grams per day during lactation.
Trace Minerals--Zinc, copper, and manganese are all important trace minerals a fetus stores in its liver for use after parturition, Huntington said. As such, he discussed pregnant mares' nutrient requirements for these trace minerals.
The NRC recommends providing 500 kilogram (1,100 pounds) pregnant mares with 100 milligrams of copper daily until eight months of gestation. At that point the NRC suggests upping the amount to 125 milligrams per day until foaling. He also noted that one study suggested oral supplementation of copper was more effective than injecting the mare with the substance intramuscularly.
Zinc is important to foals; however there are no studies evaluating the relationship between mares' zinc intake and fetal bone development, Huntington said. Manganese deficiencies have not been observed in horses, he noted.
Two other important minerals to consider when formulating broodmare rations are iodine and selenium. Selenium supplementation has been shown to increase antibody levels in foals when mares consumed 0.3 milligrams per kilogram of the diet of the mineral when compared to mares consumed the NRC-recommended maintenance concentration of 0.1 milligrams per kilogram.
Iodine, while important to daily bodily functions, can cause goiter in foals if broodmares consume an excess amount during pregnancy, Huntington said. "It appears (from published reports) that around 50 milligrams of dietary iodine is required in the daily rations of mares to produce any incidence of goiter in their foals," he said. He also noted that iodine toxicities typically result from oversupplementation, so he recommended using caution when adding iodine to the diet.
"The best way of ensuring your mare gets adequate amounts of these minerals is to use the recommended intakes of a scientifically formulated fortified feed balancer pellet or broodmare feed," Huntington said.
Vitamins--Not unlike minerals, vitamins are important to fetal growth and broodmare health. Huntington reviewed which vitamins are most crucial to consider when feeding pregnant and lactating mares:
Feeding Recommendations Finally, Huntington rendered some general feeding recommendations for broodmares before, during, and after pregnancy:
Take-Home Message Developing a feeding program for broodmares can be a daunting task. A good understanding of her nutrient requirements throughout pregnancy, however, can make the process easier and more successful for all involved.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.