Nutrition Part 1 — From Conception Through Lactation

by Dr. Stephen Duren

Performance Horse Nutrition

Wherever Thoroughbreds are grown, the goal in raising these horses is simple – produce sound, athletic horses. One factor that cannot be ignored in this quest is nutrition. Few topics stir more controversy than properly feeding horses. When do we begin feeding mares to help ensure sound foals? What influence does nutrition have on soundness of yearlings and ultimately future race performance? Do we feed Thoroughbreds in Washington or Kentucky the same way we feed in Japan, Australia, Canada and Europe? Nutrition does not need to be a confusing topic. Instead, we must understand some basic principles and make sure our horses have their nutritional needs satisfied at all stages of life from conception to the racetrack. In part one of this two part series on Nutrition – from Conception to the Racetrack – we will discuss feeding the broodmare.

Mare owners spend thousands of dollars on stud fees and shell out hundreds of dollars in veterinary care to prepare mares for breeding and foaling. Mares are expected to nurture and grow a fetus inside them for 11 months and to produce enough milk for that foal for up to six months. Furthermore, mares are expected to raise healthy foals year after year, requiring successful rebreeding while the previous year’s foal is still by her side. Because nutrition influences each stage of the broodmare’s production cycle, it is the key to the success of the breeding operation. The feeding program for top local farms, such as El Dorado Farms, top Japanese Farms, such as Shadai Farm, and top farms in Central Kentucky concentrate on proper broodmare nutrition. Based on the nutrient requirements of broodmares, feeding can be divided into distinct stages: conception, early, mid and late pregnancy, and lactation.


The effect of nutrition and body condition on reproduction in mares has been clearly illustrated. Body condition scoring serves as an effective means to determine the energy balance of your mare. Using a standardized scoring system from 1 to 9 we can estimate the horse’s body energy reserves. This information can be used to adjust feeding amounts to reach optimal body condition. When the 1-to-9 scale is utilized, a body condition of 4 or less is considered underweight, a body condition of 5 to 6 is optimal, 7 to 8 is overweight and 9 is obese. Mares coming into the breeding season with an optimal body condition score (5-6) start cycling earlier than mares with a low body condition (less than 5). Thinner mares also have difficulty conceiving and maintaining pregnancy as compared to mares in optimal body condition. Mares that are overweight or obese have decreased reproductive efficiency and often suffer from infertility. Having barren and maiden mares in a body condition of 5 and gaining weight slowly during the breeding season maximizes reproductive success. A mare with a foal by her side should have a body condition score of 6 and maintain weight during the breeding season to enhance fertility. Mares that are losing weight during the breeding season have a decreased probability of becoming pregnant and maintaining pregnancy.

Barren mares in optimum body condition going into the breeding season typically do well on good quality forage and a low intake vitamin, mineral pellet, such as LMF Super Supplement. If barren mares are overweight prior to breeding season, a forced exercise program should be implemented to help with weight reduction. These mares should also be fed a low intake vitamin, mineral pellet, such as LMF Super Supplement, to meet their mineral and vitamin requirements. A thin barren mare or maiden mare should be fed a grain concentrate to provide these mares with enough calories for weight gain. A product such as LMF Development will provide these mares with extra calories and essential vitamins and minerals.

Early and Mid Pregnancy

During early and mid pregnancy (conception through eight months of pregnancy) the developing fetus is very small, less than 20 percent of birth weight. This represents less than two percent of the mare’s body weight. The nutrient requirements for energy and protein of the mare during early pregnancy are very similar to the nutrient requirements of a non-pregnant mare. The first of two common feeding mistakes is to over feed mares during early pregnancy, causing them to become overweight. Mares that become overweight in early pregnancy tend to stay fat, resulting in a host of reproductive and health problems. The second mistake is to not feed a diet that contains adequate amounts of trace minerals. An all forage (hay or pasture) diet fed at a rate of two to 2.5 percent of body weight (20-25 lbs/day for a 1,000 lb mare) will provide most mares with adequate levels of both energy (calories) and protein. However, in several areas of the world, including the western United States, forage is deficient in several key minerals. Feeding the same low intake protein, vitamin and mineral supplement pellet that is used with barren mares during early pregnancy ensures the developing fetus is adequately fortified with essential nutrients without causing excessive weight gain in the mare. Are these minerals really important for sound foal growth? Consider the heart, lungs, nervous system and the skeletal framework of the foal is formed very early in pregnancy and deficiencies can influence further development. Further, mares that are marginal or deficient in mineral and vitamin intake have a higher rate of pregnancy loss.

Late Pregnancy

During late pregnancy (nine months to term) the fetus will gain approximately 80 percent of its birth weight. To support this rapid fetal growth, the mare’s requirements for energy, protein, minerals and vitamins drastically increase. The requirements for trace minerals are especially critical since the mare will fortify the unborn foal liver with minerals such as copper, zinc and selenium. Mare’s milk is not a good source of many trace minerals and these minerals must be stored in the foal’s liver prior to birth. The foal utilizes these minerals during the first two months of life to support proper skeletal growth. Without proper liver stores of trace minerals, the foal is predisposed to growth disorders, such as physitis and other forms of developmental orthopedic disease early in life. Compounded with an increased requirement for nutrients, the mare in late pregnancy has a limited capacity for feed intake. Intake capacity is limited due to the size of the fetus compressing the digestive system. To meet the nutrient needs of mares in late pregnancy, hay intake is often reduced and fortified grain is fed as a concentrated source of essential nutrients. In the case of El Dorado Farms, they feed LMF Development with separate formulas to compliment either Eastern Washington grass hay or timothy versus Eastern Washington alfalfa.


The lactating mare has the highest nutrient requirements of any horse on the farm. To produce milk and to repair the reproductive tract in preparation for future pregnancy, the mare requires substantial amounts of energy, protein, calcium and phosphorus. To maintain both adequate milk production and body condition, lactating mares will often need to be fed at least some alfalfa along with a properly fortified grain concentrate. A nursing foal can quickly lower condition in the mare, and lactating mares in a thin body condition will take longer to rebreed and have lower pregnancy rates compared to mares in good condition. Remember, the most common feeding mistake made with lactating mares is to underfeed them. If you can see the ribs on a lactating mare, she is too thin. El Dorado Farms utilizes the same grain concentrate they feed to pregnant mares with the volume provided increased to keep mares in the proper body condition.

The take home message for feeding pregnant mares from conception through pregnancy and then during lactation is to always provide adequate energy, protein, vitamins and minerals. For Thoroughbreds, this translates into feeding grain or supplement year round. Simply providing broodmares with an abundance of hay or pasture and a salt block will not begin to address the nutrient demands of these mares.

Further, if a mare should happen to not become pregnant or a foal is born with deformed legs, you will not be able to eliminate nutrition as a potential cause if you haven’t fed the broodmare properly. Producing a sound athletic foal is not luck; it starts with attention to detail and proper nutrition of the broodmare. Leading Thoroughbred breeding farms around the world pay close attention to nutrition.

In the next article we will discuss nutrition of the foal, weanling, yearling and finally the horse in training.

Stephen E. Duren, MS, PhD, PAS, a native of Soda Springs, Idaho, completed his Bachelor of Science in Animal Sciences at the University of Idaho. Duren earned a Master of Science and a Doctor of Philosophy in Equine Nutrition and Exercise Physiology from the University of Kentucky. Duren is recognized by the American Registry of Professional Animal Scientists as a member in good standing. He is also a member of the Equine Science Society (ESS) where he served as a board of directors’ member. Duren’s professional experience includes working as a technical services equine nutritionist for McCauley Brothers, Inc., an equine only feed manufacturer in Central Kentucky. In that role he was a consulting nutritionist for Adena Springs Farm, Darby Dan Farm, Three Chimneys Farm and Gainesway. Duren then worked as a consulting equine nutritionist for Kentucky Equine Research. This opportunity gave Duren his first international experience working with feed manufacturers in Europe, Australia and Canada. He was also responsible for large domestic clients, including Hallway Feeds and Pennfield Feeds. Duren has now formed Performance Horse Nutrition LLC, in which he consults with feed manufacturers and horse owners throughout the world. Some of the feed manufacturers that Duren consults with include LMF Feeds and Poulin Grain in the United States and Otter Co-op in Canada, Duren has also consulted directly with large horse farms, including Shadai Farm in Japan, Golden Eagle Farm in California, and Darley – Japan. Duren is a co-author of The Concise Guide to Nutrition in the Horse and is the author of  The 101 Most Frequently Asked Horse Nutrition Questions.