Broodmare nutrition – laying the foundation for a strong, healthy foal
(Article featured in Australian Performance Horse Magazine Oct/Nov 2007 pp 52-54)
Dr Caroline Foote
Equine Consulting Services
Feeding broodmares is one of the most important areas of equine nutrition, and is very often overlooked. Many in-foal mares are “good doers”, and are often provided with a very small hand fed ration, if anything at all. They are then required to rely on nutrients obtained from pasture, which may be deficient in key minerals associated with bone growth and development. In this article, we will discuss the importance of these nutrients in the gestating mare’s diet, and look at methods for improving broodmare nutrition, and ultimately foal health, growth and development.
When discussing nutrient requirements of horses, equine nutritionists will very often break requirements down into the following categories: energy, protein, vitamins and minerals.
Energy: When we talk about energy, we talk about the dietary “fuel” required for a horse to engage in its daily activities. In Australia, energy is most often expressed as MJ/kg (Mega joules of digestible energy per kilogram of dry feed). For the pregnant broodmare, energy will be used for not only maintenance of bodily functions, but will also be used for the developing foetus and also associated mammary and placental tissues. The energy requirement of broodmares in early gestation (up to 4 months of pregnancy) is similar to that of a resting horse. However, as about 80% of the growth of the foal in the pregnant mare occurs in the last four months of pregnancy, her energy requirement from approximately five months of gestation onwards will start to increase. During early lactation, the mare’s energy requirements increase further due to milk production for the suckling foal.
So what are the energy levels of horse feeds? Below are some feeds commonly used for broodmares (including basic grains) and their average energy content (as shown on relevant websites):
• Oats 11.4 MJ/kg
• Mare and Foal Pellets (Hygain) 12.0 MJ/kg
• Stud Feed (Horsepower) 12.1 MJ/kg
• Breed N Grow (Ridley Agriproducts) 12.5 MJ/kg
• Barley 12.8 MJ/kg
• Stud & Grow (Nutririce) 13.5 MJ/kg
• Breeda (Mitavite) 13.5 MJ/kg
• Corn 14.1 MJ/kg
• Biomare cubes (Prydes) 14.2 MJ/kg
Knowledge of the energy level of your mares ration becomes important when you are trying to improve, maintain or reduce her body condition. It is recommended that mares enter mid gestation in at least a moderate body condition - this means the back is flat (no crease or ridge); ribs are not visually distinguishable but are easily felt; the fat around the tail head is beginning to feel spongy; the withers appear rounded over the spine and the shoulders and neck blend smoothly into the body (NRC, 2007). Mares that are in a poor body condition in early or mid gestation should be fed additional energy to reach a moderate body score by the ninth month of gestation. Feeds higher in energy may be useful if improvements in body condition are required, while feeds lower in energy will assist in maintaining (or reducing) body condition. We will discuss methods of feeding in more detail below in “Practical Feeding of Broodmares”.
Protein - Protein is the major structural component of muscles, blood and many other tissues. A horse needs a daily intake of protein to maintain, grow and repair tissues, however, unlike energy which is stored as glycogen or fat, excess protein is not stored in the body. This means it is pointless (even in young growing horses) to feed any more protein than is recommended, it will simply add cost to your feeding program.
From month five of gestation through to parturition, protein requirements increase. During the first three months of lactation, both milk protein content and the amount of milk produced are at a peak. As a result, the amount of protein needed is greatest during this period.
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 “nonessential 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 cottonseed meal. 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 - Dietarily, minerals and vitamins should be regarded as a group rather than individually. As the intake of a mineral increases above that needed, the amount absorbed and/or excreted in the urine and/or faeces also increases. An excess amount absorbed may be harmful. That 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.
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 particular concern in rations containing high levels of grain. Excessive calcium levels are 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 particular attention should be paid to the calcium to phosphorus ratio of the entire ration when it is used as the primary roughage source.
Investigations on trace minerals have suggested that copper (Cu) supplementation of mares may be a useful treatment regime in situations where the incidence and severity of DOD are of concern (Pearce et al., 1998). Supplementation of mares at 0.5mg Cu/kg liveweight/day significantly (P<0.01) decreased radiographic indices of physitis in the distal third metatarsal bone of the foals at 150 days and the prevalence of articular cartilage lesions (P<0.05) compared to control animals grazing 4.4-8.6 mg Cu/kg dry matter. However, copper supplementation of the mares did not abolish DOD in the growing foals, emphasising the probable multifactorial nature of this condition.
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. This information has been adapted predominantly from the highly informative reference “Feeding Horses in Australia”, by John Kohnke et al (1999):
|
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 250mg/kg
|
|
Zinc
|
Reduced appetite, retarded growth, thicken 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
|
|
Adapted from: Kohnke et al. (1999)
Practical broodmare nutrition
The most common issue I encounter when evaluating broodmare diets is inadequate mineral levels provided by the rations. Broodmares are often “good doers”, and are able to maintain body condition from either grazing pastures alone, or from a small amount of a hand fed ration. Premixed (or complete) feeds are often used in this situation, these feeds should provide adequate mineral levels providing an appropriate quantity of the feed is consumed (which is sometimes not the case). If you are using a premixed feed, have a look at the back of your bag of feed - if you are not feeding the amount recommended, then your mare may be missing out on some critical minerals. Australian pastures are renowned for being low in trace minerals such as copper and zinc. Most pastures have higher calcium than phosphorus levels, however some high-oxalate pastures such as kikuyu have a very low availability of calcium. One way of getting around this problem is by supplementing the hand fed ration with an appropriate supplement containing the minerals that are low in the diet. These may be in a powdered or pelleted form, and can be a great way of providing you with the peace of mind that nutritionally speaking, you are doing all you can for your mare, and her future foal. Before adding supplements, or if you have any concerns about the nutrient intake of your mare it is advised that rations are analysed so mineral deficiencies can be determined. Ration analysis is still the most effective way of determining and correcting nutrient deficiencies in equine rations.
Equine Consulting Services provides independent nutritional advice in the form of web-based dietary evaluation, and one-on-one consultations Australia wide. For further information, please contact us.
Copyright Ó 2008 Equine Consulting Services
References:
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.
Pearce, S.G., Firth, E.C., Grace, N.D., Fennessy, P.F. (1998). Effect of copper supplementation on the evidence of developmental orthopaedic disease in pasture-fed New Zealand Thoroughbreds. Equine Vet J. 30, 183-185.
Schryver, H.F., Hintz, H.F., Craig, P.H. (1971). Phosphorus metabolism in ponies fed varying levels of phosphorus. J. Nutr. 101, 1257 – 1263.