Broodmare Diet Basics

The dietary requirements of the broodmare during pregnancy, lactation and reproduction is a topic that is often discussed and is worthy of considerable attention. After all, adequate nutrition and body condition is known to have a large bearing on reproductive function and the production of milk in the lactating mare.

Most legitimate research indicates that good, basic nutrition is the bottom line for the pregnant mare, as good nutrition is the key to providing essential nutrients to the unborn foal. Specific areas of interest and influence on development of the foal include supplementation, protein balance and quality in the diet, and optimal body score condition.


Although good basic nutrition is the cornerstone of the broodmare diet, supplementation of some minerals is advised during pregnancy. These include the staple minerals of calcium and phosphorous, which are important substances in bone development and turnover, and are in high demand for the developing foetus and the growing foal. Most research papers have shown that it is better to have these minerals in excess rather than insufficient amounts, which can result in depleted bone growth and strength.

It may also be necessary to supplement mare and foal with Vitamin E and selenium, dependant on the mare’s location and the scarcity of these two nutrients in local soil/ pasture and supplemented feed. Without these two elements, foals may be born with or develop the debilitating white muscle disease, and may be predisposed to tying up whilst intake is inadequate.

Although selenium is a mineral required in very small quantities, it is necessary for normal musculoskeletal development and works in conjunction with Vitamin E. Oral supplementation of no more than 1mg per day of Selenium is recommended where soils are deficient, and is easily transferred to the foal via the milk. Care must be taken not to over supplement, and supplement labels should be checked when used in combination so as not to overload on this nutrient.

Vitamin E is naturally found in green leafy pasture or good quality hay and has many added benefits for the mare and foal. Some premixed grains are supplemented with added Vitamin E, but this is the least reliable source as the vitamin breaks down with exposure to air and light. Vitamin E can be supplemented orally and normal horses should receive 1,000 to 2,000 international units (IU) per day of the alpha-tocopherol form (which is the most biologically active and "available" form for the horse). It is important to read the labels on your supplements, because many do not have enough Vitamin E per scoop to deliver the horses daily requirements. An easy and cost effective way to supplement is to purchase human vitamin E capsules (in alpha – tocopherol form), otherwise there are several good commercial combinations of Vitamin E /selenium available.

Body Score

Ideally, mares should be kept in a body score condition of approximately 5.5 – 7.7 (score out of 10), and have a ‘moderately fleshy’ appearance. Research has shown that mares within this range are expected to cycle earlier in the season, have fewer cycles per conception and maintain pregnancy more easily; basically this is the optimal condition for gestation, lactation and re breeding. Mares with body score conditions of less than 5 do not have sufficient stored body fat to promote efficient reproductive performance, whilst obese mares (score of 8+) may also be disadvantaged, and are linked to the incidence of development orthopaedic disease (DOD) in their foals. Table 1 indicates how body scores are assessed;

5 Moderate Neck blends smoothly into body Withers rounded over spinous processes Back is level Fat around tail head beginning to feel spongy Ribs can’t be seen but can be felt
6 Moderately Fleshy Some fat deposited on crest Fat deposited along withers May have crease down back Fat around tail head feels soft Fat over ribs is spongy
7 Fleshy Fat deposited on neck Fat deposited along withers Positive crease down back Fat around tail head feels soft Noticeable filling between ribs with fat
8 Fat Noticeable thickening of neck. Fat deposited on inner buttocks Area along withers filled with fat Positive crease down back Tail head fat very soft Difficult to feel ribs
9 Extremely Fat Bulging fat. Inner thighs rub together Bulging fat Obvious positive crease down back Building fat around tail head Patchy / lumpy fat over ribs.

Adjusted from Henneke et al. Equine Vet J. (1983) 15 (4). 371-372.


The ‘body score’ is influenced by genetic tendency, nervous disposition, the feeding program and general health and well being. The nutritional status of the mare must be constantly monitored and adjusted throughout the breeding cycle, and changes to the feeding program must be considered, including supplementation of roughage and concentrates.

Estimating Energy Requirements and Weight Gain

Throughout the first 7-8 months of gestation, the nutritional requirements of the pregnant mare does not differ that dramatically from the idle horse, however during the final trimester of pregnancy and the period of lactation, the requirements for dietary energy, protein, phosphorous and calcium increase significantly. As a general rule of thumb, dietary energy requirements increase some 10 to 20% as gestation progresses, and may increase up to 80% during lactation. Energy consumption must be adequate during these periods, otherwise milk production and reproductive efficiency can be compromised.

For a mare to maintain body condition during gestation, her weight must increase by an amount equal to the combined weight of foal, placenta and fluids. This works out to be about 9-12% of mares dry weight, i.e. predicted weight gain in the 500kg mare is a gain of 45 to 60kg plus a 2-3kg weekly gain for the final 13 weeks, bringing total percentage weight gain to 14 – 20% or 70 to 100kg.

Protein Requirements

Harrold Hintz, a professor of animal nutrition at Cornell University in the US, writes in his book Equine Reproduction that the pregnant mare requires 9-10% protein in their diet during pregnancy (between hay and grain), and up to 12% during the early stages of lactation.

The correct protein balance is an essential element to successful breeding; whilst protein deficiency can cause low birth weight and slow development in foals, a protein level that is too high has been implicated in several developmental conditions such as osteochondrosis, flexural deformities and club foot.

Whilst the percentage of protein important, the actual quantities of essential amino acids available to the mare and foal is equally crucial to optimal development of the foal; whilst two feeds may have the same crude protein levels, they will often yield vastly different levels of the essential amino acids lysine and methionine.

Roughage 2008-06-11_7

Mares need to be fed good quality roughage to maintain health and condition, which may be accessed via pasture or hay. If hay is the major roughage source, mares should receive at least 1% of their bodyweight in good quality hay per day. Ideally hay should be clean and leafy and have good aroma and colour for best palatability.

Often hay is cut too late in the season and is lower in nutrition. Although for hay producers there is an inherent conflict in cutting hay too early, the younger the plant, the better the nutrition. Generally speaking, if a large seed head is apparent, the hay is over mature and of poorer quality. As a plant produces a seed head, the fibre quality in the stem changes to lignin, which cannot be fermented in the hindgut and is of no nutritional value.

Horses tend to naturally select new, sweet feed when given the choice, and care should be taken not to feed mouldy hay or hay containing weeds alien plants such as deadly night shade which may have a toxic effect if consumed or spread to pasture through seeds germinating in manure.

Protein content of the hay will have a bearing on how much grain needs to be fed (if any at all). Quality hay is usually somewhere in the vicinity of 8 to 10%, and the breeder should invest in core samples of their hay supply to have a good assessment of the overall protein content of the diet (as mentioned above).

Concentrate Feeds

Most mares will require some form of concentrated energy feed stuff to meet the demands of gestation and lactation. At the very least, the basic grain concentrate acts as a vehicle for vitamins and mineral supplements.

The average expected dry feed consumption (both roughage and concentrate) for mares based on bodyweight ranges between 1.5 to 3% of the total body weight, whilst 2% is average. For example, a 450kg mare will require 4.5 to 6.75kg of roughage per day plus approximately 2 kg of concentrate.

Several factors must be considered when making these calculations;

  1. Feed quality and content ; mares may require a greater volume of lesser quality feed to receive the     equivalent nutritional value and protein content (although feeding poor quality feed is obviously not recommended). Similarly, different feed concentrates have different energy values; for example equal volumes of oats and corn do not have equivalent energy content.
  2. Overall protein content of the diet should be 9-10% during gestation and up to 12% during lactation.
  3. Individual metabolism; a "poor doer" might need more feed, whilst a "good doer" may make more efficient use of the provided feed and therefore requires less. Daily observation should determine changes to feed to establish an adequate volume to maintain condition.
  4. Feed water content; feeds high in moisture will be heavier whilst not necessarily delivering more energy. For example a horse at pasture will consume much more than 5-7 kg of grass per day, which is much heavier than the equivalent volume of hay, because grass has a high content of water. It is important to keep this in mind when determining feed amounts by weight.

Sticking to these basic principles should help to maintain the broodmare in the best possible condition during the annual phases of reproduction, gestation and lactation, resulting in the optimum health and productivity of both mare and foal.

By Kristen Buchanan