The moment you’ve been waiting for has arrived! Your foal has 4 feet on the ground, your mare is letting baby nurse, and your veterinarian has told you both mare and foal are healthy.

Producing high-quality milk for the foal requires a lot from your mare. Lactation puts higher energy demands on a mare’s body than any other stage of her life. [1]

To keep up with the milk requirements of a growing foal while maintaining her body weight, your mare requires a calorie- and protein-rich diet.

During early lactation, energy requirements are 84% higher and protein requirements are 232% higher. Requirements for key minerals such as calcium and phosphorus also increase.

Mares will consume more feed to match increased nutrient demands. They also use body reserves of calories, protein and minerals to support milk production.

Supplying high-quality forages and additional feeds as needed can minimize loss of body condition during lactation and help maximize milk production. Adequate vitamin and mineral supply is also important for maintaining mare and foal health. [2]

Milk Production in Horses

The first milk your mare produces after foaling is called colostrum. Colostrum is rich in antibodies and provides the foal with passive immunity. The antibodies provided in colostrum protect the foal during the first several months of life while the foal’s own immune system is developing.

Within 24 hours of birth, the mare transitions to making milk with a much different composition than colostrum. By three weeks post-partum, the milk composition becomes fairly stable for the remainder of lactation.

Mares can produce in excess of 3% of their bodyweight in milk per day. [1] This high lactation volume continues for approximately 3 months at which time production tapers off as her foal starts to eat solid food. [2]

How Much Milk Does your Mare Produce?

The amount of milk your horse produces can be estimated from her body weight and the day of lactation.

The National Research Council’s Nutrient Requirements of Horses uses the following formula to estimate milk production: [15]

Milk yield (kg / day) = (0.0274287 x BW) x d0.0953 x e-0.0043d

In this equation, d is the day of lactation and BW is body weight in kilograms (kg).

Using this formula, milk production for a 500 kg / 1100 lb horse at one month is estimated at 16.7 kg (L) per day. This will decrease to 10 kg (L) per day by 6 months of lactation.

For the first 3 months, your mare will produce roughly 3% of her body weight as milk per day. This decreases to 2% of her body weight for the next 3 months.

At 6 months of lactation, the foal is relying less on milk as he or she begins to consume more solid feeds.

Mare Milk Composition

Mare’s milk is lower in protein and fat than cow or human milk. However, it is higher in lactose (milk sugar) than cow’s milk, making it similar to human milk. [16][17][18]

Energy 480 kcal/kg
Fat 1.21%
Protein 2.14 %
Lactose 6.37%
Saturated Fatty Acids 47% of fat
Unsaturated Fatty Acids 53% of fat
Vitamin A 0.403
Vitamin D 4.93 ug/L
Vitamin E 1.13 mg/L
Vitamin K 17.93 ug/L
B-carotene 0.388 mg/L
Calcium 0.05 – 0.135%
Phosphorus 0.02 – 0.121%
Potassium 0.025 – 0.087%
Magnesium 0.003 – 0.012%


These values represent averages of mare’s milk taken across several studies. An individual mare’s milk volume and composition can be affected by several factors including: [18]

  • Breed
  • Season
  • Stage of lactation
  • Age of mare and number of previous lactations
  • Mare’s diet
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Feeding Program for Lactating Mares

Designing a feeding program for a lactating mare requires careful attention to total energy content of the diet as well as ensuring balanced vitamin and mineral levels.

As you feed your lactating mare, it is important to maintain her body condition so she can be rebred early or return to performance as soon as possible.

It is also important to provide the nutrients required to produce high-quality milk in large quantities.

Feeds may need to be added to increase fat and protein intake while avoiding excessive dietary starch from grains, which can lead to lower quality milk production.

Our nutritionists can help you formulate a balanced diet for your broodmare that meets all of the nutrient requirements for both mare and foal. Submit your horse’s diet for a free analysis online.

1) Estimate Nutrient Requirements

Mares must produce large volumes of nutritious milk and have significantly higher nutrient requirements than those required for an adult horse at maintenance.

The NRC’s Nutrient Requirements of Horses calculates the macronutrient and micronutrient needs of your mare at different stages of lactation based on her body weight. [15]

Daily Nutritional Requirements for Lactating Mares

The following chart provides approximate nutrient requirements for a 500 kg (1100 lb) mare at 3 months and 6 months of lactation. These are the minimum amounts required to avoid deficiency and do not necessarily reflect optimal intake levels.

Nutrient Amount (3 months) Amount (6 months)
Digestible Energy (Mcal) 31 27
Protein (g) 1470 1265
Lysine (g) 63 54
Calcium (g) 56 37
Phosphorus (g) 36 23
Magnesium (g) 11 8.7
Zinc (mg) 500 500
Copper (mg) 125 125
Manganese (mg) 500 500
Selenium (mg) 1.25 1.25
Vitamin E (IU) 1,000 1,000


Protein, energy and amino acid requirements are highest when the volume of milk production is highest. Along with the requirements for macrominerals such as calcium, phosphorus and magnesium, these requirements decrease as milk production decreases.

The trace mineral and vitamin requirements are higher for lactating mares than for horses at maintenance, but the requirements don’t differ by stage of lactation.

2) Monitor Body Condition

Body weight is a major factor affecting nutrient requirements during lactation. Your mare’s body weight will be highest towards the end of gestation and will normally drop during early lactation.

The extent of weight loss during lactation is influenced by: [19][20]

  • Breed
  • Foaling month of year
  • Diet quality
  • Body reserves

It is not just weight that is impacted by lactation but also body condition, which assesses fat accumulation.

Body fat reserves can have a significant impact on lactation and future reproductive performance. If your mare’s diet does not supply adequate energy and protein, she will mobilize stored fat to meet the needs of her foal. [21]

After your mare foals, closely monitor her body condition score (BCS) and observe any changes over time. Adjust your mare’s diet if required to maintain a healthy condition.

The BCS system assigns a score of 1-9, with 1 being extremely emaciated and 9 being obese. For optimal lactation and rebreeding efficiency, broodmares should be kept at a BCS of 5 – 7.

Lactating mares should not be allowed to fall below a score of 4. [2][3]

At a score of 5, the back is flat, and ribs are easily felt but not visually distinguishable. The withers round over spinous processes (projections of the spine) and the shoulders and neck blend smoothly into the body. The fat around the tailhead feels a bit spongy.

Effect on Foal Growth

In some research studies, body condition scores of the mare have been found to correlate with foal birth weight. Mares that are obese during gestation are likely to have heavier foals at birth, and vice versa. However, not all studies have shown this relationship. [22]

Foals that are born heavy are at higher risk of insulin dysregulation, orthopedic disease and osteochondrosis in the first year of life. [22]

Foals suckling on a mare with a BCS greater than 5 may also grow faster than foals suckling on a mare with a lower body condition. [20] It is not known whether this accelerated growth rate could increase the risk of orthopedic disease in growing foals.

Effect on Reproductive Performance

Broodmares with low body condition (BCS lower than 4) are likely to have delayed ovulation and impaired reproductive performance.

Mares who finish lactation at a low body condition will have a lower chance of conceiving again in a timely manner. Broodmares with a BCS less than 4 have a 20% reduced pregnancy rate compared to mares with a BCS greater than 5. [20]

As she lactates, consult with your veterinarian and equine nutritionist for strategies to maintain or recover your broodmare’s condition.

3) Monitor for Signs of Dehydration

A mare’s water intake will triple during lactation, so it’s critical to ensure she has 24/7 access to clean, fresh water. Inconsistent access to water can affect milk production, which can subsequently put the foal at risk for dehydration.

Monitor your mare and foal for signs of dehydration and ensure your mare is drinking enough water. Signs of dehydration include:

  • Sunken eyes
  • Lethargy
  • Dry and tacky gums
  • Reduced skin elasticity

Always add 1 – 2 ounces of plain salt to your horse’s feed and provide free-choice access to loose salt.

If your mare shows signs of dehydration, consider adding electrolytes to her feed program.

If your foal is showing signs of dehydration, this is very serious and needs to be addressed with your veterinarian immediately.

Dehydration in foals is commonly associated with diarrhea, which may be due to common pathogens such as rotavirus. Dehydrated foals may need to be treated with intravenous fluids to maintain fluid and electrolyte balance. [23]

4) Offer Constant Access to Clean Water

Milk contains minerals, fat, protein, and other important nutrients, but it is ~90% water. [5] Because a mare can produce up to 3 gallons of milk daily, this means she can lose 2.7 gallons of water per day through her milk.

If this water is not adequately replaced, it could leave your mare dehydrated and reduce her overall milk production. Always make sure your mare has constant access to clean, fresh, cool water.

Some owners choose to pre-emptively supplement their mare’s feed with electrolytes to promote water intake. Free-choice loose salt should also be offered at all times to meet her sodium requirement and encourage water intake.

5) Offer Ample Hay and Pasture

The average horse in moderate work eats approximately 2% of their bodyweight in hay or pasture per day. For a mare that is lactating, this increases to 3% of bodyweight per day.

For an average 1100 lb mare, she must go from eating 22 pounds to 33 pounds of forage per day. [4]

To facilitate this increased feed intage, provide high-quality forage on a free-choice basis. Grass hays harvested at early maturity or legume hays such as alfalfa are good choices for lactating mares.

If you need to ration the hay, monitor your broodmare’s body condition regularly. A decline in condition should be met by increasing the amount of hay that is offered.

Pasture and high-quality grass or legume hays should be offered to supply at least 9 kg (20 lb) of forage dry matter per day for a 500 – 600 kg mare. [21]

6) Increase Protein & Fat While Reducing Starch

Producing large volumes of high-quality milk while simultaneously keeping body condition on your mare requires careful balancing of macronutrients.

Many horse owners will simply add a high starch feed to provide additional calories required to support lactation.

Adding starch to your mare’s lactation diet may support her body condition and increase the quantity of her milk, but it can result in lower protein and fat concentrations in the milk. [7]

To keep your mare in appropriate condition, consider a high-fat, high-fibre feed. Mares’ milk is relatively low in fat meaning that dietary fat can be utilized for maintaining her own fat reserves.

Supplementing your mare with a high-fat feed or oil is a great way to minimize weight loss during lactation. [10]

Protein & Amino Acids

Pay close attention to both the total protein concentration in your mare’s diet as well as the levels of individual amino acids.

The foal breaks down milk proteins to obtain amino acids that are used to build proteins in their body. There are twenty-one amino acids that mammals use to build proteins.

Ten of these amino acids are considered essential for horses, meaning they cannot be made in the body and must be provided by the diet.

If any one of these essential amino acids is not adequately supplied in the mare’s milk, protein synthesis is limited in the foal to the rate at which the most deficient amino acid is available. [8]

Limiting Amino Acids

Lysine is considered the first limiting amino acid because the amount of lysine in the diet is most likely to be low compared to the amount required for protein synthesis. Methionine and threonine are the next two limiting amino acids. [8]

When feeding your lactating mare, take special care to ensure appropriate supplementation of amino acids – particularly lysine and methionine. During lactation, her lysine requirement will increase from 36 grams per day in late gestation to 66 grams (for an average 1100 lb mare). [9]

Feed sources that provide high levels of lysine include:

  • Soybean meal
  • Roasted soybeans
  • Canola meal
  • Amino acid supplements

Soybean or canola meal are feeds that are high in protein and have a high percentage of lysine to support maximal protein synthesis.

The recommended amount to feed will depend on your forage quality and your horse’s body weight. It is often still necessary to add additional amino acids which can be achieved by supplementing pure amino acid.

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  • Hoof & coat quality
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Mad Barn’s Three Amigos is a pure amino acid supplement containing optimal levels of lysine, methionine and threonine in a balanced ratio.

7) Supplement With Multiple Feedings of Concentrates

Due to the high-calorie requirements during late gestation and lactation, most mares receive grain supplementation. Lactating mares are often fed 4 – 5 kg (10 – 15 lb) of commercially produced grain per day. [2]

As a rule, horses should only be fed 0.5% of their bodyweight in grain at one time. For an 1100 lb mare, this is 5.5 lb per meal. If feeding more than this in a single meal, the risk of colic increases sixfold. [6]

Many complete feeds are not adequately fortified with vitamins and minerals to meet the lactating mare’s needs. Feeding below the recommended amount can result in deficiencies that affect the mare and foal’s health.

It is often more cost-effective to use high-quality feeds such as soybean or canola meal, forage cubes/pellets, beet pulp, rice bran and/or oil to meet her energy and protein needs.

These feeds should be fed alongside a balanced vitamin and mineral supplement to ensure nutrient requirements are met.

8) Meet Vitamin and Mineral Requirements

Providing your mare with vitamins and minerals in appropriate amounts and ratios is critical for both the health of your mare and the growth of your foal.

It is highly recommended to submit a hay sample for analysis to determine the mineral content of your horse’s forage. With a hay analysis, your equine nutritionist will be able to design a feeding program that balances mineral ratios to support milk production, mare health and foal development.

A number of health issues in the foal can be attributed to mineral imbalances in the diet of the lactating mare. Some examples include:

  • Excess or insufficient iodine can cause foal goitre or enlargement of the thyroid. [12]
  • Excess phosphorous in relation to calcium can inhibit calcium absorption, causing hyperparathyroidism and abnormal bone development. [13][14]

Calcium and Phosphorus

In particular, calcium and phosphorus levels are important to balance carefully in the mare and foal’s diet.

The mare will mobilize mineral stores in her body to deliver certain nutrients into milk if her diet is deficient. For example, lactation increases bone mineral turnover to provide calcium for milk.

Markers of bone mineral loss are increased during early lactation in mares. These markers decline as lactation progresses and mares are likely able to regain bone mineral density following lactation. [21]

Low calcium diets in lactating mares can make bone demineralization worse but supplementing calcium and phosphorus above requirements does not appear to decrease demineralization. [21]

If additional calcium is required in the mare’s diet, the following feeds are recommended:

  • Alfalfa or clover hay/pellets/cubes
  • Beet pulp
  • Calcium carbonate (limestone)

If additional phosphorus is required, consider adding the following sources:

Vitamin and Mineral Supplements

In addition to calcium and phosphorus, many other minerals are required to make milk and support foal development. Mad Barn’s Omneity is a comprehensive vitamin and mineral supplement designed to balance most forages and grain-based feeding program.

Feeding Omneity to your lactating mare will help to meet the needs for calcium, phosphorus and organic trace minerals while also supplying complete B-vitamin fortification, digestive enzymes and active yeast cultures.

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Additional Ways to Support Mare & Foal

In addition to providing adequate nutrition for your lactating mare and foal, you can adopt the following practices to further support their health:

  1. Probiotic supplementation: Yeast supplementation increases antibody content of mare colostrum to provide more immune defences to the foal. [24] Probiotics support fibre digestion and nutrient absorption.
  2. DHA supplementation: This omega-3 fatty acid derived from marine sources supports foal brain development and mare reproductive health. [25][26]
  3. Raising your mare’s feed: Preventing the foal access to the mare’s feed by raising it off the ground allows more precise supplementation of their individual diets to support their needs.
  4. Encouraging water intake: Soaking your mare’s grain and hay helps to further increase water consumption to support milk production and help prevent dehydration.

Lactating mares have increased calorie, protein and micronutrient requirements to support their health and meet the needs of the foal.

These requirements can be met by high-quality forages, cost-effective commodity feeds and appropriate vitamin/mineral supplementation.

It is strongly recommended to submit a hay sample for analysis and consult with an equine nutritionist to balance your mare’s diet before, during and after lactation.

Submit your mare’s diet online for a free consultation and expert help with designing a balanced feeding program to support lactation.

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  3. Carroll, C. and Huntington, J. Body condition scoring and weight estimation of horses. Equine Vet J. 1988. View Summary
  4. Guay, A. The effects of Matua bromegrass hay on gestating and lactating mares and their foals. Texas Tech University. 2001.
  5. Musaev, A. et al. Mare’s Milk: Composition, Properties, and Application in Medicine. Arch Razi Inst. 2021. View Summary
  6. Lardy, G. and Poland, C. Feeding and Management for Horse Owners. ND State Uni. 2001.
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  24. Ayad, M.A. et al. Effect of supplementing arabian and barbe pregnant mares with
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