Feeding Pregnant Broodmares

Feeding broodmares (and growing foals) is one of the most important and challenging areas of equine nutrition. Nutrient requirements increase markedly as the mare gets closer to foaling, and it is the correct intake and balance of these nutrients that will assist in producing a strong and healthy foal. Optimum fertility and proper balanced nutrition are interrelated. An adequate energy intake, matched to the mare's requirements to achieve and maintain optimum condition, is paramount to success in horse breeding.

It is well known that the diet of the pregnant mare can influence the “soundness” of her future foal. Low levels of minerals and trace minerals in pregnant mare diets have been shown to increase the risk of skeletal disease in foals and as a consequence, it is now normal farm practice for most mares to be fed supplemented diets at least during the last trimester of pregnancy if not all the way through pregnancy.

Mare body weight is also of critical importance with recent research suggesting a link between excess body condition of mares and subsequent skeletal disease in their foals (Foote, 2013). Pregnant mares should be maintained in moderate body condition (condition score 2.5-3) which can be particularly challenging when faced with good seasons (i.e. plenty of grass). Feed and supplement choices then become even more important to ensure an adequate supply of critical nutrients whilst minimising unnecessary body weight gain.

The first eight months of pregnancy

During the first eight months of pregnancy, most mares can maintain themselves on good pasture with minimal supplementary feed, as long as good quality lucerne or meadow hay is fed during times of reduced pasture availability or quality. Australian pastures are typically deficient in trace minerals copper and zinc and may also be low in calcium. Deficiencies and imbalances of these minerals in pregnant mare diets can lead to a debilitating condition in growing foals commonly known as Developmental Orthopaedic Disease. For this reason, suitable “pasture balancer” supplements such as FERAMO^® with CHROMIUM and CAL-PLUS^® with BIOTIN should be offered with a small amount of chaff to ensure adequate nutrient supply. Pelleted broodmare rations are suitable for maintenance during dry seasons, or in the early winter months when pasture is poor, particularly as pregnancy progresses.

Overweight mares should not be put on a weight reduction programme during the first 90 days of pregnancy. Research has shown that pregnant mares fed diets containing energy levels below their needs, had a higher risk of early embryonic and foetal abortion during the first three months of pregnancy, compared to mares kept at a constant bodyweight.

After the first 90 days of pregnancy an overly fat mare can be safely put onto a well monitored weight reducing programme. It is essential to adjust the feed intake and ensure exercise to achieve a weight loss of no more than 1% of the mare's bodyweight each week (5 kilograms for a 500 kg mare), until she reaches and maintains the desired body condition score between 2.5-3. Continued supplementation is advised during this time and the addition of good quality protein (such as extruded full fat soyabean meal) may assist in maintaining muscle condition.

The last three-four months of pregnancy

About 80% of the growth of the foal in the pregnant mare occurs in the last four months of pregnancy. As a consequence, from about month nine of gestation onwards, the broodmare’s requirements for minerals increase significantly, and then increase further during lactation. While nursing, the foal must rely on its own body stores of some of the minerals until it begins to eat significant amounts of pasture or its own feed. It is therefore important that the pregnant mare receives adequate amounts of zinc and copper to allow the foetus to accumulate sufficient body stores before birth.

While increased levels of energy and protein are required in order to support the growth of the foal during this time, many mares considered to be “good doers” may still be able to maintain appropriate body condition on minimal feed and pasture supplemented with good quality lucerne hay. It becomes even more important to ensure a high quality trace mineral supplement and calcium supplement is offered to ensure continued supply of adequate nutrients for optimal foal development.

Loss of condition in a mare during the last three to four months of pregnancy does not affect her foal's body weight at birth, unless she becomes very thin. However, the loss of body reserves may decrease the mare's colostrum and subsequent milk production so that her foal's growth rate and immune status may be compromised. As a commercial breeding proposition, a mare must be able to be bred and conceive again within 1-2 months of foaling. Failure to supply adequate nutrition to maintain bodyweight after foaling may reduce subsequent fertility and conception.

During the last three to four months before foaling, it is best to separate heavily pregnant mares from other mares and horses. A young or timid mare must be able to consume sufficient supplementary feed to meet her needs without being harassed or bossed away from the feeders. It is good practice to provide one extra feed bin or locate 2 or 3 feed bins away from the main feeding area for timid younger mares so that they are able to obtain their fair share of feed.

Basic nutritional requirements & management of pregnant broodmares

Energy

For the pregnant broodmare, energy will be used not only for maintenance of bodily functions, but will also be used for the developing foetus and associated mammary and placental tissues. Additional energy in the form of concentrate feed may be required to meet the demands of the unborn foal and provide reserves to prepare the mare for lactation.

Protein

Protein provides the amino acid building blocks for the development of the unborn foal. Good quality protein with adequate lysine and other amino acids is essential for foetal development, with the requirement increasing by 30% during the last three months of pregnancy.

It is important to ensure that the broodmare’s diet not only contains adequate protein but that the protein is of “high quality”. Proteins composed of a high proportion of the “essential amino acids” are referred to as high-quality proteins. Those containing a high proportion of “non-essential amino acids” are low- or poor-quality proteins. Ensuring high quality protein is particularly important in growing foals and lactating mares, and of lesser importance in adult horses providing the feed contains sufficient protein to meet the horse’s dietary protein needs. In one study, mares fed high quality protein containing essential amino acids lysine and methionine prior to and following foaling produced milk with higher protein content during the first month of foaling compared to mares that were not on the supplemented feed. Foals born from these supplemented mares also had significantly higher growth rates during the first seven weeks of life compared to foals born from unsupplemented mares (Glade and Luba, 1987). Protein feeds that contain high levels of essential amino acids include soyabean meal, canola meal and lupins. Copra and sunflower contain relatively low levels of essential amino acids, and are therefore generally unsuitable as the sole protein source in growing foal rations.

Minerals and vitamins

In the broodmare diet and indeed in any equine diet, vitamins and minerals should be considered as a group rather than individually. As the intakes of certain minerals increases above requirements, the amount absorbed and/or excreted through urine or faeces also increases. Excess amounts absorbed may be harmful, while excess amounts not absorbed may bind other minerals, decreasing their absorption and possibly resulting in a deficiency of these minerals.

It is therefore the balanced amount of all minerals in the diet that is important. Indiscriminately adding one or even several minerals to the diet is likely to be more harmful than beneficial. Therefore, minerals should not be added to the diet unless it is known which ones and how much are needed.

Developmental Orthopaedic Disease – the importance of balanced mineral levels

One of the most debilitating conditions in growing foals can be caused through inadequate and inappropriate levels of minerals in broodmare diets. The condition, commonly known as Developmental Orthopaedic Disease (DOD) encompasses a range of skeletal problems associated with growth and development in the foal. Developmental Orthopaedic Disease is a multifactorial condition, but nutrition has been shown to play a key role. As far as broodmare nutrition is concerned, the minerals of particular concern are calcium, phosphorus, copper and zinc.

Deficiencies and imbalances of calcium and phosphorus have been widely recognized as causes of DOD. Absolute intakes of calcium and phosphorus must not only be adequate, they must also be in an acceptable ratio to each other (ideally 1.8:1). If calcium intake is less than phosphorus intake (ratio less than 1:1), calcium absorption may be impaired. Even if the diet contains adequate calcium, excessive phosphorus intake may cause skeletal abnormalities (Schryver et al., 1971). This is of concern in rations containing high levels of grain. Excessive calcium levels are also of particular concern if the phosphorus level in the diet is not adequate. Lucerne hay is high in calcium compared to phosphorus (can be about 6:1), and attention should be paid to the calcium to phosphorus ratio of the entire ration when it is used as the primary roughage source.

Balanced calcium, phosphorus and trace mineral supplementation is essential during pregnancy to compensate for soil and feed deficiencies and imbalances. This can be achieved by feeding FERAMO with CHROMIUM and CAL-PLUS with BIOTIN. FERAMO with CHROMIUM is a vitamin and trace mineral supplement, while Cal-Plus contains 3 different forms of calcium plus the co-factors needed to enable the calcium to be taken up from the bowels and utilised within the body. Supplementation will assist in maintaining appropriate mineral and vitamin supply during pregnancy and will help to reduce the risk of skeletal disease in foals.

Consequences of vitamin & mineral deficiencies & excesses

The consequences of prolonged deficiencies and excesses of some of the minerals and vitamins relevant to broodmares (and foals) are shown in the table below.

Table 1. Importance of minerals and vitamins in broodmare nutrition

Nutrient	Deficiency symptoms	Excess symptoms
Calcium	Bone deformities/skeletal weakness, joint problems and rickets in young horses	May reduce uptake of trace minerals iron, zinc, magnesium and manganese
Phosphorus	Inadequate bone formation, retarded growth, infertility and poor conception, lowered milk production	Bone weakness, decreased uptake of calcium
Copper	Reduced cartilage formation in foals	Horses can tolerate high levels of copper in the diet, maximum tolerable level 250 mg/kg
Zinc	Reduced appetite, retarded growth, thickened skin and hair loss	Enlarged joints and lameness in foals
Iron	Anaemia	Excess iron toxic to young foals
Manganese	Irregular ‘season’ cycles in mares, joint cartilage and bone formation reduced	Anaemia and infertility
Selenium	Lower fertility in mares, poor muscle development and pale, weak muscles in foals (White Muscle Disease)	Loss of hair of mane and tail, bent legs in foals, lameness and hoof separation
Iodine	Deficiency in late gestation can result in foals born dead or weak, goitre in mature horses	Infertility and abortion in mares (most commonly due to excess seaweed meal as a natural supplement). Foals can develop enlarged joints and contracted tendons if excess is fed
Vitamin A	Loss of appetite, poor growth, infertility in mares	Ill-thrift, rough coat, weakness, anaemia
Vitamin D	Depression of calcium uptake, weak bones, swollen joints, slow closure of growth plates in bone and reduced growth rate in young foals	Promotes increased uptake of calcium, especially when phosphorus is in excess, increased calcification in tissues
Vitamin E	Weight-loss, subcutaneous swellings, rough coat, decrease in the animal’s immune response to infectious diseases, impairs reproduction in both males and females of many species of animals	Excessive vitamin E is not general concern in horses, but other species display impaired bone calcification

Adapted from: Kohnke et al. (1999).

Fibre: hay and pastures

Provision of adequate fibre (hay/chaff/pasture) is essential for efficient digestion, however fibre sources vary widely in terms of mineral and trace mineral supply.

Australian pastures

The type of pasture grazed influences the amount of calcium and phosphorus available, and the balance between them. Table 2 outlines average nutrient composition of typical non-tropical Australian pastures relative to the recommended requirements of a 500 kg broodmare in late gestation. As you can see, the levels of zinc and copper in these pasture samples are significantly lower than recommended levels.

Table 2. Average nutrient composition of non-tropical Australian pastures relative to the recommended dietary requirements of a broodmare in late gestation.

		Average Australian Pasture "Non-tropical"	Broodmare Late-Gestation Requirements
Calcium	g/kg	5.5	5.0
Phosphorus	g/kg	3.5	3.0
Magnesium	g/kg	2.8	0.8
Potassium	g/kg	25.0	2.6
Sodium	g/kg	1.3	1.1
Chloride	g/kg	11.0	4.1
Sulfur	g/kg	2.7	1.5
Iron	mg/kg	409.0	50.0
Zinc	mg/kg	37.3	40.0
Copper	mg/kg	7.4	10.0 - 25.0
Manganese	mg/kg	103.1	40.0

Average Australian Pasture Data supplied by Equine Consulting Services Pty Ltd.

Grasses are generally lower in calcium and higher in phosphorus than legumes. Where mares are grazing predominantly grass pastures, such as fescues, paspalum and ryegrass, extra calcium should be provided to meet requirements. Lucerne or legume-based pastures, usually provide more than adequate calcium, but are low in phosphorus, which can result in a relative deficiency of phosphorus in heavily pregnant, grazing mares. In this case, the amount of lucerne hay should be restricted, and replaced with mixed hay, or a blend of 50:50 lucerne and cereal chaff as the base for the hard feed mix given daily, depending on availability.

In tropical areas, where pasture contains high levels of oxalate containing grasses such as Setaria, Green and Blue Panic, Buffel, and even heavily fertilised Kikuyu in sub-tropical areas, an extra supplement of calcium (e.g. CAL-PLUS with BIOTIN) is essential to counteract calcium binding by oxalates in the small bowel.

Exercise

Exercise is required to keep a mare in a fit condition for foaling. Grazing provides adequate exercise in most cases, although a heavily pregnant mare in the last month prior to foaling is often less agile, and may prefer to graze within easy range of a supplementary feed area. Locating feeders and waterers well apart will help to encourage exercise. Undulating country may also help pregnant mares to exercise and maintain physical fitness. Where a mare is confined to a small area, walking in hand for 15-20 minutes daily will help to promote feed utilisation and fitness. It is risky and uncomfortable for a heavily pregnant mare to be exercised under saddle, or by lungeing.

Older mares

Healthy, well cared for mares often breed regularly until over 20 years of age. Mares over 16 years of age should receive extra protein and calcium daily because older horses are less efficient in absorbing these nutrients. It is also wise to crush the grain for an aged mare with poor teeth to ensure she obtains the full benefit from the concentrate feed. She should also be provided with a more energy dense ration and additional protein, at approximately 200 g (1 cup) of additional extruded full fat soyabean meal for every 250 kg body weight, as protein utilisation is not as efficient.

A wet feed containing about one kilogram wet weight cooked barley per 200 kg body weight, may be given twice a week as an appetising feed in late pregnancy, particularly during very cold, wet and windy weather.

Careful attention to balanced, adequate, but not excessive nutrition for broodmares provides the best start to a foal’s life. Energy, protein, minerals and vitamins are all essential components of the diet and care should be taken to make sure that they are available to the mare and developing foal in the correct quantity and balance, particularly in the last 3 months of pregnancy.

References

• Foote, C.E. (2013) Pers. comm
• Glade, M.J., Luba, N.K. (1987). Benefit to foals of feeding soybean meal to lactating broodmares. Proc Equine Nutr & Physiol Soc Sym, pp 593 – 597.
• Kohnke, J.R., Kelleher, F., Trevor-Jones, P. (1999). Feeding Horses in Australia. RIRDC Publication No 99/49.Lewis, L.D. (1995). Developmental orthopaedic diseases in horses. In: Equine Clinical Nutrition: Feeding and Care. Williams & Wilkins, USA.
• Lewis, L.D. (1995). Equine Clinical Nutrition. Williams & Wilkins, USA, pp 15 – 20.
• NRC (National Research Council). 2007. Nutrient Requirements of Horses, 6th ed. Washington DC: National Academy Press.
• Schryver, H.F., Hintz, H.F., Craig, P.H. (1971). Phosphorus metabolism in ponies fed varying levels of phosphorus. J. Nutr. 101: 1257.