Over recent years, much more research effort has been focused on the nutritional requirements and feeding management of the broodmare and her foal up until weaning. Although large sums of money are often outlaid for the purchase of a breeding farm and stock, upgrading facilities and promotion, relatively little attention has been given to ensuring the optimum nutrition of the broodmare.

To provide the breeder with an economic return, a mare at stud should produce a foal in each season she is mated. Although fertility and the conception rate decreases as a mare ages, careful attention to nutrition and a well planned feeding program in preparation for breeding will help to ensure an optimum conception rate for each mare. An adequate energy intake, matched to the mare’s needs, is essential to achieve and maintain an optimum body condition for breeding.

Horse breeders tend to over-feed pregnant mares and growing horses relative to their needs. They often under-feed dry mares ("empty" or non-pregnant) and lactating ("wet") mares maintained on predominately grazing pasture. Under these conditions, inadequate nutrition can affect a mare’s subsequent fertility and conception rate.

In a lactating mare, the drain of milk production is superimposed on the energy requirement to maintain fertility and conception, especially in a marginally under nourished mare with a foal at foot. This invariably results in less than optimum fertility and a reduced chance of the mare getting back in foal during the peak period of her lactation between 4-10 weeks after foaling to ensure the desired 12 month foaling interval.

If the drain of lactation is not compensated for by an increased energy and major nutrient intake, a mare’s fertility will decline, followed by a reduction in milk production, and finally a loss of body condition.

There are a number of dietary management guidelines that must be considered when preparing a mare to be bred to increase her chances of conceiving and establishing a viable pregnancy to full term. The body condition of a mare at breeding can be evaluated against condition score standards that have been developed to monitor energy stores within the body relative to fat distribution. The concept of condition scoring provides a standard for breeders to evaluate the probability of a mare breeding successfully.

Ideally a mare should be fed to achieve a moderate to good condition prior to breeding.

As a guideline, a mare in moderate to good condition has a ‘fleshy’ covering over her ribs and pin bones, with the outline of her ribs just visible.

There are a number of relationships that have been established by review of a large number of research studies.

• A poorly fed or thin mare, in below average condition, will have a delayed onset of oestrus and irregular oestrus cycles in contrast to a well fed mare.

• A thin mare will come into season and cycle, but may fail to ovulate, conceive or maintain her pregnancy. Such a mare should have her feed intake increased, commencing 2 - 5 weeks before the breeding season, so that she is gaining weight when bred.

• A mare that is thin or below moderate condition at breeding, is still able to foal down a foal of average birth weight at full term 11 months later.

• Unless a mare’s body weight is improved after foaling, she will have a higher risk of lower fertility and embryonic loss when she is bred during the peak of her lactation.

• Even without weight loss, studies have shown that a thin mare has longer intervals between foaling and ovulation, requires more cycles per conception, has an overall lower conception rate and an increased early embryonic death rate than a mare in a moderate to average, or fat condition.

• An inadequate intake of protein in the ration, even with adequate energy, can delay the onset of oestrus and decrease overall fertility, possibly due to failure to ovulate, although a mare may show her normal oestrus behaviour and cycle length.

• A well fed, but not overly fat mare will normally ovulate earlier, with more regular cycles, than a fat or overweight mare fed on a maintenance or weight reduction diet.

• A fat or overweight mare will cycle and conceive successfully if her nutritional intake is maintained during the pre-breeding period, oestrus and conception, and for 90 days after conception so as to avoid any loss of body weight.

• Any reduction in the feed intake of a fat mare immediately before the breeding season to reduce her body weight will retard the onset of oestrus, and increase the time interval between oestrus cycles.

• It is unwise to start a weight-reducing program on an obese mare within the last 2 months before breeding.

• A lack of feed during the previous lactation period may reduce the fertility of a mare in the following season, even if a mare has gained weight and is in good condition at breeding.

There are a number of dietary management guidelines that should be considered to ensure a lactating mare maintains her milk production and fertility.

• A mare that foals late in the season may be unable to maintain her body weight if she receives a lower nutritional intake once pasture is grazed down or becomes less productive. The combination of consuming a lower energy diet and increasing lactation demand will drain her energy reserves and result in loss of body weight. Ovulation in this case can be suppressed and she may not be able to get back in foal, even when given supplementary feed to increase her energy and protein intake.

• Although studies have not linked early foaling, or an increased difficulty in foaling, with heavy or obese condition in a mare, many breeders claim that excessive condition can result in a higher incidence of foals born with limb deviations.

• An obese mare at foaling that is slightly underfed to meet her needs, will maintain her fertility and ability to conceive, as well as milk production for the growth of her foal. If body fat reserves are lost rapidly on a low energy diet, the mare’s fertility and then milk production will be adversely affected.

• If a mare has a consistently lower feed intake than necessary to meet lactation demand, she will lose condition and is less likely to breed successfully in the time remaining in the breeding season.

• It is a common belief that an obese mare does not produce as much milk due to fat occupying room in her mammary gland. Studies have shown that an obese mare has a similar milk yield to a moderately conditioned mare, but her foal may grow at a slightly lower rate during the first two months.

• Excess energy intake in a lactating mare does not increase the fat or protein content of the mare’s milk, but in fact lowers them slightly.

• There is no practical advantage in overfeeding a lactating mare to boost her milk production, except that the subsequent fertility and conception in a very thin mare will be improved by providing more feed so that she can gain weight.

• If a mare is in very poor condition, feeding to gain weight during the early lactation period will help to improve fertility, but the rate of conception may be less than optimum. Her milk supply may be lower during the peak period of her lactation from 4-10 weeks after foaling, and the weight of her foal at three months of age less than average.

• A thin mare that is put onto higher levels of feed at foaling will have a conception rate similar to a well conditioned mare.

• An overly fat mare can afford to lose some weight slowly without affecting overall fertility.

• It is important to avoid significant weight reduction during the first three months after foaling, as milk production may be reduced and retard the growth rate of the foal. If the mare is bred and becomes pregnant, then she has a high risk of early embryonic abortion if she loses significant weight during the first 90 days after foaling.

• A lack of adequate energy and protein intake during the first two months after foaling usually affects fertility first, then milk production, and finally body condition. It may not be visibly apparent that a large mare, weighing 500-550kg is lower in condition until she has lost 50kg in body weight.

• The failure of early foaling mares to cycle and conceive is largely due to lack of adequate energy intake in the 2-3 months following foaling.

Once a mare foals and begins to produce milk to feed her foal, she must be provided with an increased intake of energy, protein, calcium, Vitamin A and other vitamins and minerals to meet her needs. A lactating mare requires more of these nutrients than a racing or performance horse in medium-heavy work.

During early lactation, as compared to late pregnancy, a mare's requirement for energy increases by 70%, protein by 60%, calcium by 66%, phosphorus by 25% and double the volume of water intake. (Refer to Table 1).

The energy and protein drain of lactation in a mare may affect her chances of cycling and conceiving when she has a foal.

Any mare in thin condition has less chance of getting back in foal as reserves are drained by the onset and increasing demands of lactation.

The comparative energy needs for pregnant and lactating mares are illustrated in the Table 1 below:

*MJ DE = Megajoules Digestible Energy

Source: NRC (1989)

The rate of early embryonic loss in lactating mares bred soon after foaling is around 17%, as compared to 6.3% for non-lactating mares. The high rate of early embryonic loss may be related to the retention of uterine fluids, or influenced by the increased energy and protein demands to fuel increased milk production for the first 10 weeks after foaling. Lactation represents a heavy drain on energy stores in a thin mare in poor condition.

An inadequate intake of protein in a lactating mare can result in 20% lower bodyweight of her suckling foal at three months of age. The ration should contain 12-14% crude protein during the first three months of lactation to maintain the mare's condition and milk supply. A good quality 14-16% crude protein ration given to all mares will also provide nourishment for the foal and encourage it to develop an individual eating habit and minimise nutritional stress and set-back in growth and development at weaning.

• An older mare over 16 years of age should be provided with a 14-16% protein ration because protein is not as well absorbed from the small intestine as a horse ages.

A mare that loses weight after foaling may take an additional 30 days to come into season and fail to cycle regularly. If a mare is under nutritional stress and in poor condition at foaling, a delay of up to 60 days may occur before she recommences her breeding cycles.

It is important to regularly monitor the body condition of mares with foals grazing on pasture during the less productive time of the season, where reduced pasture quantity and quality may decrease the total energy intake, and subsequently affect fertility and milk production. It is essential to provide supplements of hay or extra concentrate before a loss of condition is apparent.

• If a mare is bred and conceives during lactation, then after weaning the ration intake can be slowly reduced over a 1-2 month period to the ration given for a pregnant mare.

• The mare should not be allowed to become too fat.

• The ration intake and exercise level of an overweight mare should be adjusted to avoid her losing more than 1% of body weight (about 4.5-5.0kg) each week. After weaning, a non-pregnant mare’s ration can decreased over a 2-3 week period to the ration intake recommended for a resting mare.

A lactating mare grazing sparse or dry pasture should be supplemented with good quality mixed grass and legume hay, with extra concentrates to ensure an adequate intake of protein and energy. Hay alone, provided in an amount that the mare can eat, may still be 30% energy deficient without a additional concentrate ration. Therefore, the energy deficiency must be made up with a concentrate feed provided on a daily basis.

Observations suggest that lactating mares grazing predominantly on lucerne or legume based pastures appear to breed more successfully when given a concentrate feed containing additional phosphorus (for example, containing 2% dicalcium phosphate), 1500iu Vitamin E, at least 40,000iu Vitamin A and a range of trace-minerals, including iodine and selenium.

An adequate intake of calcium and phosphorus is essential during lactation, complemented by a balanced increase in the intake of trace-minerals. Studies have shown that supplementing copper, zinc and manganese to lactating mares does not elevate the level of these trace-minerals in the mare's blood or milk, or increase uptake by the foal. If copper is supplemented to foals to help prevent abnormal cartilage development and lessen the risk of DOD related joint disease, it should be added to the feed provided for the growing foal, such as in a dedicated creep feed. Supplementation at a rate of 50-75mg of copper, zinc and manganese per kilogram of concentrate is considered adequate to meet the essential trace-mineral needs likely to be deficient in the diet of heavily pregnant and lactating mare, as well as a foal sharing its mother’s feed.

Generally, if the intake of energy is sufficient to maintain an adequate or rising plane of nutrition in a mare prior to breeding, then the diet will contain adequate protein to meet the needs of a dry mare and a mare during early pregnancy.

Feeding a diet containing more than 9% crude protein has no direct benefit in improving the fertility of mares that have an adequate intake of energy.

A low protein diet, which can be a problem when mares are grazed on grass dominant pasture, even with an adequate intake of energy, can delay the onset of oestrus. Subsequent fertility may be reduced by a failure to ovulate, even if the mare exhibits normal cycle length and 'in season' behaviour.

The energy and protein needs are significantly increased during the last month of pregnancy and for the first 3 months of lactation. An adequate intake of balanced pasture mix containing 60% grass and 40% legumes will generally provide a sufficient quantity and quality of protein without limiting important amino acids for a lactating mare.

The quality of protein, related to the lysine and other essential amino acid content, is important in pregnant and lactating mares.

Although an adequate and balanced intake of vitamin A and vitamin E has been shown to be essential for optimum fertility and conception in a mare, especially on dry pastures, supplementation with either vitamin alone unless there is a significant deficiency may not improve the overall fertility of a mare.

Where there is limited grazing, a ration containing 30-33% dry roughage (10% moisture), and 65-70% dry concentrate feed may be required to meet energy and other nutrient needs at peak of lactation.

The quality of protein in the diet can affect the protein content of a mare’s milk. An increase in milk protein occurs when higher quality soyabean protein constitutes 50% of the protein intake, with a corresponding increase in the growth rate of suckling foals.

However, supplementing with an excessively high protein concentrate feed above 24% crude protein may reduce pasture intake in grazing mares. It has been shown that mares and growing foals grazing mature grass based pasture may receive adequate energy, but may be marginally deficient in protein, including the amino acid threonine, to satisfy the needs of heavy lactation and growth.

An intake of 0.75kg/100kg body weight or more of alfalfa (lucerne) hay daily will satisfy the need for threonine and many other essential amino acids in mares grazing on grass dominant pastures.

A diet containing less than 8% crude protein in a mare grazing grass dominant pasture can result in a 20% lower body weight of her foal at three months of age.

As a guideline, when pasture intake falls short of needs, a supplementary ‘hard’ feed given to a lactating mare to maintain her body weight should contain 12-14% crude protein to meet protein and amino acid requirements.

The intake of calcium and phosphorus may not be adequate during winter and spring when low calcium grasses dominate the pasture mix. Supplementary calcium and protein, either as good quality alfalfa (lucerne) hay, or in a concentrate feed, should be provided under these conditions.

The nutritional needs of growing horses have been a focus for research over the past two decades. These studies have provided better guidelines with which to formulate rations to achieve optimum growth and steady controlled development in athletic breeds of horses.

Overfeeding, in an attempt to produce well-grown young horses in good condition for sale, and with sufficient development for training as 2-3 year olds, can lead to rapid growth rates. This has been associated with an increase in limb abnormalities and unsoundness of young horses.

The combination of adequate, rather than excessive nutrition, and opportunity for free exercise each day are the two most important factors that influence limb development and soundness in young horses.

It is important that a newly born foal receives an adequate intake of colostrum of at least 750-1000mL/100kg body weight during the first 12-16 hours of life. Colostrum provides both essential antibodies to give the foal immunity and protect the developing gut against infection during the first 2-3 weeks of life, as well as energy, protein and other nutrients to meet its needs during the first few days of life.

The growth rate of a young foal can be monitored by the increase in body weight, height at the withers and overall development of body proportions.

Although mares are not selected for their milk production and only have two relatively small milk glands (udders) with limited storage capacity, they produce a volume of milk each day comparative to grazing beef cows. Foals nurse up to 105 times daily for about 1½ minutes at each drink during the first week of life, reducing in frequency to 65 times daily as lactation develops, and 35 times daily by 2 months of age. Regular and frequent suckling helps stimulate an increased production of milk to satisfy the foal’s demands, prevents overload of the digestive tract and bathes the gut with protective local IgA antibodies against bacterial and other diseases during the first 3 weeks of a foal’s life.

Milk yield in mares is influenced by the mare’s genetic ability for milk production, feed intake during the late stage of pregnancy, and by availability of water and intake of energy and protein during lactation. The growth rate of her foal at foot is relative to the milk yield of the mare.

When consuming an adequate amount of milk and grazing to meet its needs, a foal will double its birth weight in the first month, and double it again by 3 months of age. After 6 months, usually at about the time of weaning, the growth rate slows down until adult body weight is achieved by 4½-5 years of age, relative to the breed.

Mare’s milk contains sufficient energy, protein and other major nutrients to meet the needs of the young foal during for the first 4 weeks of its life. The growth rate of the foal is dependent on the milk yield of the mare during the first 2 months of life.

A Standardbred horse foal maturing to 425-450 kg body weight requires approximately 9 kg milk for each kilogram increase in body weight at 7 days of age, 13 kg at one month of age and 15 kg at 8 weeks of age. These intervals correspond to the peak of lactation of a mare.

A foal may drink up to 18 kg of milk daily and require an intake of 16.4 kg of milk per kg of liveweight gain at 8-10 weeks of age. Under warm conditions, a foal may drink 5.5 litres of water daily at 10 weeks of age.

After the peak of lactation, which occurs from 4-10 weeks after foaling, the energy and protein content in a mare’s declining milk production is unable to meet the foal’s needs for growth, although adequate calcium, phosphorus, trace-minerals and vitamins will normally be provided in the milk.

Good quality green pasture, containing 9-10% crude protein on a dry matter basis, will help make up the shortfall in energy and protein as growth needs of a young foal exceeds that supplied by milk.

As pastures dry off, or are grazed down, a supplementary concentrate feed is necessary for both the mare and her foal to enable the young foal to maintain an optimum rate of growth.

A supplementary creep feed, containing 16-18% crude protein (with an energy density of 13-14MJ/kg, in a pelleted feed, or a mix containing crushed or extruded grains), will make up shortfalls in energy and protein intake required by young growing foals. The concentrate should contain at least 20-25% by weight of a high quality protein meal, such as soyabean, canola meal, or skim milk powder for young foals to meet protein, lysine and other essential amino acid requirements for growth.

A 12-14% crude protein feed based on pellets, crushed or extruded grains for a mare and her foal to share, will help to meet the increased nutritional demands of the foal as milk production by the mare declines towards weaning time.

The higher energy content of the supplementary ration will also help ensure the mare maintains an optimum body weight and the chances that she will be able to breed and support the critical 90 days of early pregnancy. Any weight loss caused by the drain of lactation must be avoided, particularly during mid to late summer when pastures dry off.

It is important to evaluate and monitor a foal’s rate of growth and development to achieve an optimum and steady, rather than a maximum or rapid rate of growth. The incidence of limb deviations and enlarged growth plates on joints associated with Developmental Orthopaedic Disease (DOD) is largely influenced by diet and exercise in the young growing horse from 3 – 9 months of age.

Selenium deficiency in young foals prior to weaning that are grazing on selenium deficient pastures can result in White Muscle Disease, which is characterized by poor muscle development, weakness and inability to exercise normally.

A supply of good quality water, located in a suitable safe and low trough to allow foals to drink, is important under warm conditions. In colder countries, observations indicate that only 50% of foals drink water on a regular basis before weaning.

Aldred J (1998) Developmental Orthopaedic Disease in Horses Research Paper No. 97/79 Rural Industries Research and Development Corporation, Barton, ACT Aust. 1995

Cunha TJ Horse Feeding and Nutrition Edition 2, Academic Press California USA 1991

Frape, D Equine Nutrition and Feeding, Edition 2, Blackwell Scientific Publications, Oxford, UK 1997

Kohnke, JR Feeding and Nutrition of Horses – Making of a Champion Vetsearch International Sydney 1998 p. 71-75

Kohnke JR, Kelleher F, Trevor-Jones P,
Feeding Horses in Australia – A Guide for Horse Owners and Managers, Rural Industries Research and Development Corporation Publication Number 99/49 1999 p. 75-89, 101-105

Lewis LD Equine Clinical Nutrition – Feeding and Care Williams and Wilkins Baltimore USA 1995

McMeniman, N Nutrition of Broodmares and Growing Horses, In Equine Nutrition and Pastures for Horses Workshop, Rural Industries Research and Development Corporation, Barton, ACT Aust. 1995 p1-31

McMeniman, N (1996) Nutrition of Grazing Broodmares and Growing Horses Aust.Vet.Journal Vol.74 p64-70

National Research Council Nutrient Requirements of Horses Revised 5^th Edition, National Academy Press, Washington DC, USA, 1989 pp.

Rose RJ, Hodgson DR Manual of Equine Practice Edition 2, Saunders Philadelphia USA 1999 p. 664-667, 676-680

Stowe, HD (1965) Reproductive performance of barren mares following vitamins A and E supplementation Proc. 131 AAEP Convention New Orleans p. 81-93