Breeding Mare Nutrition

A breeding mare is not just a horse that happens to reproduce. She's an animal with dramatically different nutritional demands than a maintenance or performance horse. Breeding, pregnancy, and lactation are metabolically expensive. They require more calories, more protein, more minerals, and more vitamins than any other phase of a horse's life except maybe growing from birth to adulthood. Understanding what your breeding mare needs lets you support her health, improve fertility, and set her foals up for success before they're even born.

Breeding season starts the conversation. Mares in estrus and cycling regularly need extra nutrition compared to non-breeding horses. They're expending energy on hormonal cycles and reproductive processes. During breeding season, mares benefit from higher condition scores, typically a 6 or even 7, to support fertility and regular cycling. A mare that's too thin often doesn't cycle well or can have inconsistent heat cycles. Getting her into good condition before breeding season starts matters enormously for whether she'll conceive.

Once a mare is pregnant, her nutritional needs increase progressively through the eleven months of gestation. Early pregnancy, the first few months, doesn't dramatically increase requirements above breeding season maintenance. But the last third of pregnancy, when the foal is growing most rapidly, the mare needs significantly more calories and minerals. She's not just eating for herself anymore. The developing foal is drawing substantial nutrients from her diet and those nutrients have to come from somewhere.

Lactation is where things get really demanding. A mare producing milk for a growing foal can need 50 percent more calories than a non-breeding horse of the same size. She's producing a gallon or more of milk daily, and that milk is the foal's primary nutrition for the first few months of life. If the mare doesn't have adequate calories, she'll lose condition rapidly while nursing. She might recover that condition later, but the foal suffers immediately if the milk supply drops from inadequate mare nutrition.

The real challenge is that many horse owners don't recognize how much more mares need at different stages of the breeding cycle. They feed the same amount year-round and wonder why their mares get thin during pregnancy or lactation, or why they don't cycle well during breeding season. Feeding a breeding mare correctly is about understanding the different phases and adjusting nutrition accordingly. It's also about planning ahead rather than reacting to condition problems after they happen.

The caloric demands of breeding are real and substantial. A non-breeding mare at maintenance might need 20,000 to 25,000 calories daily depending on size and metabolism. A mare in breeding season and cycling regularly needs about 10 to 15 percent more calories to support reproductive function. Early pregnancy adds another 5 to 10 percent on top of that. Late pregnancy and lactation can require 50 percent more calories than maintenance. That's a huge difference. A 950-pound mare eating 15 pounds of hay daily for maintenance might need 20 to 22 pounds of hay plus grain during late pregnancy and early lactation.

Protein becomes increasingly important through breeding and pregnancy. Mares need adequate protein to support muscle maintenance, immune function, and fetal development. A maintenance horse might need 0.5 to 0.7 grams of protein per pound of body weight. A pregnant mare in late pregnancy needs 0.8 to 1 gram per pound of body weight. A lactating mare needs 1 to 1.2 grams per pound. That's almost double what a non-breeding horse requires. The protein also needs to be high quality with balanced amino acids, particularly lysine and methionine. Poor-quality protein won't cut it when demands are this high.

Calcium and phosphorus become critical and must be in correct ratios. A pregnant mare has massively increased calcium needs because she's building a foal's skeleton. The fetal skeleton contains enormous amounts of calcium. Her own bone density can be compromised if she doesn't get adequate calcium during pregnancy. Phosphorus also increases, but calcium should always exceed phosphorus in the ratio. Ideally, calcium should be about 1.5 to 2 times the phosphorus. A mare deficient in calcium while pregnant can develop health problems and foals can be born with skeletal weakness.

Vitamins, especially vitamin A, vitamin D, and the B vitamins, need to increase during pregnancy and lactation. Vitamin A supports immune function and fetal development and is critical for foal vision and bone development. Vitamin D supports calcium absorption and bone development in the fetus. B vitamins support energy metabolism when demands are high. Many commercial feeds for mares are formulated with these needs in mind, but if you're feeding a mare hay and grain without supplementation, she might be running short, especially late in pregnancy.

Micro-minerals like zinc, copper, and manganese matter more during breeding and pregnancy than during maintenance. These minerals support immune function, bone development, and metabolic processes. A mare deficient in zinc might have poor hoof quality, reduced fertility, or give birth to weak foals with poor immune function. Copper deficiency can affect connective tissue and bone strength in the developing foal, leading to developmental orthopedic disease. These are often overlooked but important for long-term foal soundness.

Water demand increases significantly during pregnancy and especially during lactation. A lactating mare needs substantially more water to produce milk. She might drink 2 to 3 times as much water as a non-lactating horse. Always ensure she has access to clean, fresh water at all times. Dehydration during lactation can drop milk production immediately, affecting foal growth.

Feeding during breeding season means getting your mare into good condition first. Aim for a condition score of 6 to 7 before breeding starts. This condition supports fertility, regular cycling, and gives her reserves for the demands of pregnancy and lactation. Thin mares cycle irregularly or not at all. If your mare is below a 5, spend a month or two building condition before breeding season starts. Some owners won't breed thin mares at all, seeing condition score as essential for success.

Feeding strategy during breeding season is relatively straightforward but requires consistency. Maintain good condition with quality forage and appropriate grain to keep her at that condition score. If she's on pasture during spring and summer, she might get adequate nutrition from grass. If she's on hay, she'll need supplemental grain, especially if the hay is not of top quality. Track condition monthly and adjust grain as needed to maintain the target score.

Once a mare is confirmed pregnant, early pregnancy feeding is much like breeding season feeding. Maintain condition and good nutrition. The fetus is still small and demands are not dramatically different from breeding season maintenance. Some owners make the mistake of drastically increasing feed too early in pregnancy, wasting resources. Early pregnancy doesn't require dramatic feed increases. Save the big increases for late pregnancy when the foal is actually growing rapidly.

Late pregnancy, the last three months, is when feeding increases significantly and intentionally. Increase hay by 10 to 15 percent if possible, or replace some hay with higher-quality forage like alfalfa or clover-timothy blends. Increase grain to ensure adequate calories and protein. Many breeders add a specialized mare and pregnancy supplement or a higher-protein concentrate during late pregnancy. This is the time when the foal is growing fastest and the mare's demands peak.

Throughout pregnancy, feed high-quality forage. Moldy hay or poor-quality hay puts the mare at risk for problems and doesn't provide adequate nutrition for fetal development. If you're feeding older, lower-quality hay, especially during pregnancy, supplement with a commercial concentrate designed for pregnant mares or add oats, alfalfa, and other high-nutrient feeds. Quality matters more during pregnancy than at almost any other time.

Lactation is where massive feed increases happen. Plan to increase total calories by 40 to 50 percent from what the mare ate during pregnancy. A mare that was eating 20 pounds of hay and 5 pounds of grain might need to move toward 22 to 24 pounds of hay plus 8 to 10 pounds of grain, or equivalent calories in other forms. Lactating mares benefit from higher energy feeds like oats, fat supplements, or high-calorie complete feeds. Some mares can't eat enough volume to get adequate calories just from hay, requiring grain and supplements.

Easy keepers present a different problem during breeding. While an easy keeper at maintenance might barely need grain, a pregnant or lactating easy keeper still needs adequate nutrition and mineral supplementation. She won't lose condition easily, but she can become deficient in protein and minerals if fed only hay. An easy keeper mare might maintain weight on less grain than a hard keeper, but she still needs quality nutrition during breeding phases. Don't let her easy-keeping tendency fool you into underfeeding during pregnancy.

Hard keepers have it harder during breeding. A hard keeper mare that struggles to maintain condition at maintenance absolutely needs aggressive feeding during pregnancy and lactation. She might need 30 to 40 percent more feed than a hard keeper non-breeding horse. Many breeders of hard keeper mares add fat supplements or high-calorie feeds to support lactation and recovery. A hard keeper mare nursing a foal can become concerningly thin without adequate support. Some hard keeper mares never fully recover condition while nursing and can take years to rebuild weight.

Performance mares that are still in work while breeding need careful consideration about workload. Some owners breed mares while keeping them in light work, which is possible with excellent nutrition. A mare in light work during early to mid pregnancy needs even more calories to support both work and fetal development. Never breed a mare and put her in hard work. Light work and excellent nutrition is manageable. Hard work plus pregnancy is stress and metabolic demand without adequate benefit to anything.

Young mares having their first foal before age five or six need special consideration. They're still growing themselves while supporting pregnancy and lactation. A young mare might need 10 to 15 percent more feed than a mature mare of the same size during breeding. Their bodies are still developing and they need extra resources for both their own growth and the foal's development. Young mares often benefit from higher-quality nutrition than older mares to support both demands.

Older mares often become harder keepers as they age. A 15-year-old or 20-year-old mare that's still breeding might need more feed than a younger mare of the same size. She digests feed less efficiently and her metabolism has changed over years. If you're breeding an older mare, expect her to need more supplemental nutrition than in her younger years. Weight loss during lactation accelerates with age and recovery takes longer.

Underfeeding during late pregnancy or lactation is the biggest risk to mare and foal. A mare that's underfed will lose condition rapidly, especially during lactation. Thin lactating mares often also produce less milk, affecting foal growth and development. A foal that doesn't get adequate milk from the dam will be smaller and weaker. The effects of poor nutrition during pregnancy and lactation can affect the foal for life, including reduced height, bone problems, and developmental issues.

Calcium deficiency is a specific risk during pregnancy. A mare that doesn't get adequate calcium while pregnant can develop metabolic problems and give birth to foals with developmental orthopedic disease. Foals born to calcium-deficient dams often have bone problems, weak joints, or orthopedic issues that persist into adulthood. This is preventable with adequate feeding and supplementation.

Feeding change mistakes happen when owners increase feed suddenly. A mare being transitioned to significantly higher grain intake can develop colic or other digestive problems if the change happens too fast. Always increase grain gradually, adding a pound or two weekly until you reach the target amount. Digestive upset during pregnancy is dangerous for both mare and foal.

Foal prematurity or weakness can result from poor mare nutrition during late pregnancy. Foals born to well-nourished mares are stronger, have better immunity, and develop normally. Foals born to mares that were underfed are more likely to be premature, weak, or have developmental problems. Premature foals often have respiratory issues and poor survival rates.

Mares that are overfed during late pregnancy and lactation might develop excessive weight and metabolic problems. This creates insulin resistance, laminitis risk, and damages joints. The goal is adequate nutrition, not excess. A condition score of 6 to 7 during lactation is ideal, not 8 or 9.

Postfoaling problems can sometimes be traced to poor nutrition during pregnancy. A mare that had inadequate nutrition during pregnancy is more likely to have uterine problems, infections, or slow recovery after foaling. Her own health is compromised if she wasn't adequately fed while pregnant. Recovery from foaling is also harder for underfed mares.

Start planning mare nutrition at least three months before breeding. If she's thin, spend those months building condition. If she's at good condition, maintain it with consistent feeding. You want your mare to be at a condition score of 6 to 7 and in excellent health before breeding starts.

Use a specialized mare and pregnancy supplement or feed during late pregnancy and lactation. These are formulated for the specific needs of pregnant and lactating mares, with balanced calcium, phosphorus, vitamins, and minerals. They make feeding correctly much easier than trying to formulate it yourself. Quality products designed for this purpose are worth the investment.

Weigh your mare or estimate her weight accurately so you can calculate feed amounts correctly. Use body condition scoring to track condition throughout breeding and pregnancy. Don't just feed an arbitrary amount and hope it works. Track condition monthly and adjust based on what you see. Document everything so you have records of what worked.

Keep foals growing well after birth by ensuring the mare is well-nourished. Foal growth depends entirely on milk supply, which depends entirely on mare nutrition. A foal that gets excellent nutrition during the nursing phase starts life with better growth and development. This investment pays dividends throughout the foal's life.

Consider mineral balance carefully. If your hay is deficient in certain minerals, supplement. Many horse owners test their hay annually to know what they're actually feeding. This helps you know whether supplementation is adequate or if you need more. Testing takes the guesswork out of mineral balance.