How to feed your pregnant and lactating mare

The hope is that after foaling, there will be both a healthy, strong foal and a well-being mare. A well-balanced diet for the mare throughout pregnancy and lactation is crucial for the mare's well-being, but also for the foal to get a good start in life and develop into a healthy and sustainable horse.

Prepare the mare for breeding
Even before breeding, it's important that the mare's diet is well adapted to her needs. A lack of nutrients reduces the chance of the mare becoming pregnant and also increases the risk of early miscarriage. Optimal body condition is crucial for successful breeding and continued pregnancy. Mares scoring above 5 on the Henneke body condition scoring system have been shown to conceive more easily than those that are underconditioned. It's also important to ensure that the mare's vitamin needs are met year-round to ensure successful breeding.

The vitamin content in fresh grass is high, but due to long winters here in the Nordic region, we need to store forage as hay or haylage and feed it to horses for most of the year. Since vitamins are not particularly storage-stable, the vitamin content in stored forage is lower than in fresh grass. Normally, the vitamin needs of a hobby horse are met by forage. However, a supplement of vitamins A, D, and E may be beneficial to ensure that a breeding mare receives the amount she needs, as the need increases during pregnancy and lactation. It is especially during the months when the mare does not have access to fresh grass that a vitamin supplement may be relevant.

Illustration of the body condition scoring scale after Henneke et al., (1983).

Nutritional needs change during pregnancy
During the first months of pregnancy, the mare's nutritional needs are the same as when she is not pregnant, as the fetus does not grow much in the beginning. It is during the last four months of pregnancy that fetal growth takes off significantly, and this is when the mare's nutritional needs increase. The energy requirement increases by 15-30% in the last months of pregnancy. The protein requirement also drastically increases in the pregnant mare, partly due to the foal's skeletal growth, which requires large amounts of protein. To meet the needs for energy and protein, it is important to have nutrient-rich roughage of high quality. In Feeding Recommendations for Horses from SLU, an energy content over 9 MJ/kg DM and a ratio between digestible crude protein and energy over 8 is recommended. Since the fetus takes up a lot of space in the mare's abdominal cavity towards the end of pregnancy, it may be difficult to consume the large amounts of roughage needed to meet the nutritional requirements. In that case, it may be appropriate to add a more nutrient-dense supplementary feed to the diet.

In addition to an increased need for energy and protein, the need for minerals also increases during the later part of gestation. It is important that the mare receives a sufficient amount of microminerals during the last two months because during this time the foal builds up a reserve of microminerals in the liver. There is a lot of calcium in the mare's milk but not significant amounts of microminerals. Therefore, the foal needs to store enough microminerals in the liver to manage until it starts to eat solid food.  

What the mare eats can have a big impact on the foal's health.
Both undernourishment and overnourishment in broodmares have been shown to negatively affect the foal's health. Foals of mares that were undernourished during pregnancy were not initially affected and were born with normal weight. It is later in their development that delayed development of testicles, thinner tubular bones (the type of skeleton found, for example, in the horse's legs), and reduced insulin sensitivity (a risk factor for laminitis) have been observed. Reduced insulin sensitivity has also been seen in foals where the mare was instead overweight. These disturbances in the foal's development can have a significant impact on its health and sustainability throughout life.

Feeding large amounts of starch has been shown to negatively affect the development of the foal with an increased risk of osteochondrosis (Peugnet and others, 2015). A good guideline to avoid overfeeding starch to the pregnant mare is to keep the intake under 1g of starch per kilogram of body weight per meal.

Foal's first months
The newborn foal has no large energy reserves so it is important that it gets milk from the mare as quickly as possible. The first milk the mare produces, colostrum, is rich in nutrients, but it's not only nutrients that the foal needs to ingest with the colostrum. It also contains antibodies necessary for the foal to gain resistance to infections. In many animal species, antibodies are transferred through the placenta. This is not the case with horses; instead, the foal must ingest enough colostrum to survive. Horses are hindgut fermenters and are entirely dependent on having a large number of microorganisms in the hindgut that can convert fibers in roughage into substances that the horse can absorb and use as energy. The foal lacks these microorganisms at birth and therefore needs to receive microorganisms from the mare via the colostrum to establish a stable microbiota.

During lactation, the mare's nutritional needs increase further, as milk production is a demanding process. The energy requirement of the mare is very high at the beginning of lactation, approximately double compared to maintenance needs. The protein content in the milk is highest at the beginning of lactation (1st-3rd lactating months) and then gradually decreases, which means that the mare's protein needs are also highest at the beginning and then decline.

Weaning
Weaning always means stress for the foal. Often, growth diminishes during a period when contact with the mare and the mother's milk is no longer available. It is beneficial if the foal has had the opportunity to eat foal feed already when it is with the mare so that it has gotten used to it by the time of weaning. It remains important that the foal’s nutritional needs are met during the first years when growth is high.

Be careful not to forget the mare during weaning. It's easy for all the focus to be on the foal and its feeding. The mare needs to be ready again for a demanding challenge to be able to deliver another healthy foal. If the mare is to be covered again after foaling, it is important to ensure she is in good condition to manage another pregnancy. She must have enough resources both to provide what the foal needs and for her own nourishment, and also for a potential new foal growing in the womb.

Text written by: Hanna Lundqvist, St. Hippolyt (2021)
Feed Advisor & Agronomist with a Master's in Animal Science

Recommended products for broodmares from St. Hippolyt
NaturMüsli Easy Breeder is a breeding feed for breeds or individuals that cannot tolerate large amounts of starch and sugar. The nutritional content is tailored for pregnant and lactating mares, without adding large amounts of energy.

Also Beta-Carotene Sea-Y-Mix recommended for breeding horses. The high needs of breeding horses for ß-Carotene are not covered with feed during winter. Deficiencies can lead to late or weak estrus, impaired follicle formation, and poor embryonic development. ß-Carotene should therefore be given to broodmares and stallions from November to April.

Sources
Chavatte-Palmer, P., & Robles, M. (2019). Developmental programming: Can nutrition of the mare influence the foal's health?Brazilian Journal of Animal Reproduction,43(2), pp. 168-183.
Henneke, D., Potter, G., Kreider, J., Yeates, B. (1983). Relationship between condition score, physical measurements and body fat percentage in mares. Equine Veterinary Journal 15, p. 371–372.
Jansson, A. (Ed.). (2013). Challenge recommendations for horse. Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences.
Lawrence L, Camargo F. University of Kentucky Cooperative Extension Service. Feeding the broodmare: four easy steps.
Möller, J. (2005). Vitamin A and E in relation to horse feeding.
Peugnet, P., Robles, M., Mendoza, L., Wimel, L., Dubois, C., Dahirel, M., Guillaume, D., Camous, S., Berthelot, V., Toquet, M.P., Richard, E., Sandersen, C., Chaffaux, S., Lejeune, J.P., Tarrade, A., Serteyn, D. & Chavatte-Palmer, P. (2015). Effects of moderate amounts of barley in late pregnancy on growth, glucose metabolism and osteoarticular status of pre-weaning horses.PLoS One,10(4), e0122596.
Planck, C., & Rundgren, M. (2005). The Nutritional Needs and Feeding of Horses. Nature and Culture.Facts etc..