By understanding the mare’s nutritional needs during each stage of her reproductive cycle, an intelligent and cost effective feeding program can be designed and implemented.
Because nutrition influences each stage of the broodmare's reproductive cycle, nutrition management may determine the success of a breeding program. Nutrition influences conception, early embryonic loss and abortion, foal vigour at birth, ability to recover from foaling and conceive again, and the growth and soundness of the suckling foal.
From breeding through to weaning, the nutritional demands of any broodmare are divided into a number of key periods: conception and early pregnancy, mid pregnancy and the last trimester of pregnancy, early and late lactation, and weaning. The nutrient requirements for these stages differ and adjustments should be made to the mare’s feeding programme to accommodate these differences. In addition, the age of the mare, the number of previous pregnancies, current climatic conditions and forage quality need to be considered when drawing up a feeding programme.
Research has shown a direct link between the effect of nutrition and body condition on reproductive efficiency in mares. Mares coming into the breeding season in good to moderate body condition start cycling earlier than mares in poor body condition and mares have better conception rates when in a rising plane of nutrition.
Thinner mares have difficulty conceiving and maintaining pregnancy. Research from South Africa has shown that mares in a poor nutritional state in early pregnancy had more early embryonic deaths than mares in a good nutritional state. As many early embryonic deaths occur in the first 40 days of pregnancy this is a nutritionally critical time period, especially for the under-weight broodmare.
Young maiden mares which have recently come out of racing will have nutritional requirements above that of a mature broodmare as they are still growing. Some maiden mares recently out of racing may be both underweight and stressed. Thin maiden mares should be fed so that they are gaining weight and in a positive energy balance coming into the breeding season.
Obesity on the other hand has also been linked with reproductive problems in the mare. Obese mares can have longer intervals between ovulations, due sometimes to a persistent corpus luteum. Some obese mares can continue to cycle throughout the winter when typically reproductive cycling is shut down. This affects breeding efficiency in the Spring. Obesity can cause decreased insulin sensitivity in horses, which is associated with decreased reproductive function in broodmares. Obesity in mares in late gestation can also lead to difficulties during foaling.
Ideally overweight broodmares should not be put on a weight reduction programme during the first 90 days of pregnancy, as pregnant mares on diets containing energy levels below their needs have a higher risk of early embryonic death as well as foetal abortion during the first three months of pregnancy, compared to mares kept at a constant bodyweight.
When commencing a weight reduction production programme it is important that the weight is lost gradually over a period of time, and that the mare be provided with a high quality protein and vitamin/mineral supplement or stud balancer during this time.
It is vital to regularly assess body condition throughout all stages of reproduction and modify calorie intake as necessary. The most common mistakes made in feeding broodmares are overfeeding during early pregnancy and underfeeding during lactation.
Non-lactating mares in the first four months of pregnancy should not need high levels of supplementation. Quality forage should provide the mare with adequate levels of energy and protein to meet her requirements during the first trimester.
Prior to the publication of the most recent version of Nutrient Requirements of Horses, industry professionals divided a mare’s gestation into two distinct nutritional periods: early gestation (the first eight months) and late gestation (the last three months), also known as the last trimester.
Recommendations up until this point suggested that the pregnant, non-lactating mare’s nutrient needs did not differ greatly from those of an adult horse at maintenance, as foetal growth during the first six months is quite slow. By month seven the foal is only 20% of its birth weight and weighs less than 2% of the mare’s weight.
However, ‘Nutrient Requirements of Horses’ now suggests that the provision of certain vital nutrients should be increased long before that to meet the requirements of, not only maintenance of the mare’s body weight and foetal growth, but also the nutritional expenditures involved in the creation and development of non-foetal tissues.
Quality pasture would be sufficient for most non-lactating mares in mid pregnancy but could possibly be deficient in certain key vitamins and minerals. It may be necessary at this stage to supplement the mare’s diet to ensure adequate nutrients are available to support foetal development.
During the last three months of pregnancy the mare’s energy requirements increases significantly as this is when rapid growth of the foetus and associated membranes occurs. The foetus can increase in weight by up to one lb/day during the last 90 days of gestation, accounting for over 60% of total foetal growth.
To support this growth, the mare’s need for most nutrients, but especially calories, protein, calcium, phosphorus and vitamin A, substantially increases. Failure to meet these requirements may compromise foetal growth and bone development.
Meeting the mare’s requirements for trace minerals (iron, zinc, copper and manganese) is especially critical during the last trimester as the foetus accumulates stores of minerals in the liver to support rapid growth post parturition. The foetus has developed this nutritional strategy of storing trace minerals during pregnancy because mare’s milk is quite low in these elements. Without proper liver stores of trace minerals, the young foal may be predisposed to bone development disorders. Research has shown that it is not possible to make this up by supplementing the foal with trace minerals after birth.
Loss of condition in a mare during the last three months of pregnancy does not affect the foal's body weight at birth, unless the mare’s weight loss was substantial. Loss of body reserves may however decrease the mare's colostrum and subsequent milk production so that the foal's growth rate and immune status may be compromised.
Birth weight is dependent to a large degree on protein deposition, it is critically important to meet the mare’s requirements for protein during gestation. Recent research has found that protein restriction during the last 90 days of pregnancy has no affect on the quality of colostrum, but the ability of the newborn to absorb the essential antibodies of the colostrum is reduced by 50%. Mares over 16 years of age should receive extra protein and calcium during gestation and lactation as older horses are less efficient in absorbing these nutrients.
The mare in the last month of pregnancy has a limited capacity for feed intake due to the size of the foetus compressing on the digestive system. Hay intake is often reduced so protein and energy requirements may need to be met through feeding additional concentrate.
Early lactation is a period of substantial physiological stress for the broodmare. The lactating mare’s nutrient needs are greater than those of any other class of horse with the possible exception of the racehorse in training. During this time the mare must recover from the stress of parturition, produce milk and re-breed.
The lactating mare has an increased requirement for water, protein, energy, calcium and phosphorus. If her feed intake is not increased to provide these nutrients, she will maintain milk production by using her body stores for energy, amino acids and minerals, causing loss of weight and loss of body condition as well as mineral losses. If the nutrient deficiency is extreme, milk production and re-breeding efficiency will both decrease.
A 500 kg mare will yield about 15 kg of milk per day during early lactation, equivalent to 5½ kg of hay, and up to 10 kg per day during late lactation. That energy needs to be replaced to avoid going into negative energy balance and losing bodyweight. Energy needs during lactation increase approximately two-fold over maintenance.
One of the most important periods for sound growth is the time prior to weaning when the foal is still nursing the mare. Studies of the incidence of osteochondritis dissecans (OCD) have shown that the disorder is very dynamic during the early months of life and that the highest recorded incidence occurs at five months of age. Many foals are still not weaned at this age and are reliant on nutrition from the mare’s milk and pasture. Supplementing the foal with additional nutrients at this stage is advisable, through a balancer, concentrate or feed additive.
Peak milk production occurs roughly six to twelve weeks after foaling. As the mare’s milk production decreases, decrease her feed intake to maintain proper body weight. At weaning time, reduce the feed further. Gradual feed reduction the week prior to weaning will reduce milk production enabling the mare to dry up quicker.
In feeding mares and foals it is important to start from the ground up. Good pasture management is integral to good broodmare nutrition. As pasture quality can be so variable, time spent on improving grassland is never wasted. Of all the nutrient sources available, grass is the cheapest and arguably the most important. Grass quality is also very dependent on weather conditions. Sunny humid conditions improves grass quality, where as wet weather can ‘dilute’ the nutrient profile of grass. Wet years make meeting the mare’s requirements through supplementing the diet more important.
Grazing also acts as a good form of exercise for the heavily pregnant mare, helping to maintain fitness and tone, a huge advantage at foaling time. If winter grazing is not a possibility due to poaching and extreme weather conditions it is advisable to provide broodmares with some form of turnout, such as an all weather paddock or sand ring.
A forage analysis should be the starting point of any winter feeding programme as the quality of hay and haylage can be so variable. Two primary factors that influence forage quality are nutrient concentration (protein, calories, vitamins and minerals), and nutrient digestibility. Both of these are heavily influenced the stage of maturity of the forage plant. The mineral status of a forage tends to reflect the mineral content of the soil that it is grown on.
The absorption and metabolism of minerals is interrelated. The ratio of certain minerals is every bit as important as the actual amount fed. For example copper deficiencies in horses can be caused by a lack of copper in the diet or induced due to interactions with other minerals in the diet. Zinc and molybdenum are known as copper antagonists as they can interfere with copper absorption in horses. A forage or soil analysis will highlight if excesses or deficiencies of certain minerals exist. It is important to note that wet weather conditions can lead to increased levels of antagonists in the soil.
If a deficiency or mineral imbalance exists feeding a mare forage that has been conserved from the pasture that she grazes on is only compounding the problem. Feeding plans need to be formulated based on a forage analysis to ensure adequate levels and the correct ratios of minerals are in place. Supplementing to counteract the deficiency or purchasing forage from another location may be advisable.
Care must also be taken in choosing a forage and bedding this year that it has been harvested and stored properly, as wet summer conditions made it very difficult. Stud owners should be concerned about the presence of moulds and mycotoxins. In breeding animals mycotoxins negatively influence the reproductive cycle, in particular conception and foetal development.
The mare’s feeding program should be adjusted to accommodate the differences in requirements throughout gestation and lactation. A stud balancer may be more than sufficient to meet her requirements during gestation provided she is on good quality forage that is meeting her energy requirements.
When forage alone is not meeting the mare’s energy requirements a concentrate designed specifically for the broodmare can to be fed. When fed at the recommended daily intake provided by the manufacturer, the concentrate will meet all of the mare’s requirements.
For mares that do not require such a high intake of concentrate, a stud balancer or a feed supplement that supports growth can be used in conjunction with the concentrate. The balancer/ feed supplement maintains a constant base nutrient intake to meet the mare’s requirements, while energy intake can be adjusted through the concentrate.
Alternatively alfalfa chaff, beet pulp, cereals and fat supplements can be used to increase the energy density of the feed. Alfalfa chaff and beet pulp are excellent sources of energy. They are both very high in calcium and would compliment a cereal diet, but not balance it. They would also compliment forage with a low calcium/high phosphorus levels. Alfalfa chaff is also a good source of magnesium and lysine, both essential in the growth and development of youngstock. A stud balancer/feed supplement would be necessary in order to provide a complete balanced diet.
Cereals are also an excellent source of energy. It is important to note that cereals have an inverse calcium phosphorus ratio of 1:4. High phosphorus levels interfere with the absorption of calcium. Ideally the calcium phosphorus ratio should be fall between 1.5-2:1. Incorrect ratios can lead to problems in bone development. Using cooked/processed cereals will enhance overall digestion, improving feed utilisation and lessening the chance of digestive related disorders.
Oil and fat supplements are also a good source of calories for the broodmare. Flaxseed oil would be the oil of choice for the broodmare as it not only acts as an energy source but also provides the mare with the essential fatty acids, omega 6 and omega 3, at similar ratios to that found in grass, 1:4. Omega 6 and omega 3 are fatty acids that cannot be synthesised by the horse and so need to be provided in the diet. Cereals and preserved forages have reverse ratios of these fatty acids, approximately 10-16:1. Mares on a hay and/or cereal diet would benefit from flaxseed oil supplementation. Emulsified oils allow for better absorption and utilisation.
Nutritional management is a simple, yet cost effective tool that can be applied to ensure normal reproductive cycles, improved conception rates and increased pregnancy maintenance in mares to ensure overall reproductive success. By understanding the mare’s nutrient needs during each stage of her reproductive cycle, an intelligent and cost effective feeding program can be designed and implemented.
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. Make dietary changes slowly and consult your veterinarian or equine nutritionist with any questions or concerns.
- Feeding before and after foaling – Dr. Jennifer Stewart
- Feeding the Broodmare – Joe Pagan
- Feeding the Mare – Dr. Lori K. Warren