Colostrum is the first milk that a mare produces after foaling. It is particularly rich in antibodies, which provide immunity for newborn foals.

Foals are born without a fully developed immune system and rely on a passive transfer of antibodies from their dam to help build their immune defenses. Consuming enough high-quality colostrum in the first 6 – 12 hours of life is critical for the foal’s health and survival.

Colostrum contains antibody proteins called immunoglobulins and other factors, which help combat diseases that could otherwise be deadly for foals.

Foals that do not get enough high-quality colostrum are at greater risk of infections, such as diarrhea caused by pathogens. If your foal cannot be nursed for any reason, donor colostrum should be fed to support immunity. Another option is to infuse equine plasma directly into the circulation to deliver antibodies.

You can determine whether your foal has consumed adequate colostrum with an IgG test from your veterinarian to measure the immunoglobulin concentration in your foal’s blood.

Importance of Colostrum for Foals

Foals are born with limited immune defences. They do not receive any immunity from their dam while in the uterus. [1]

When a foal is born, she primarily relies on colostrum from her mother to obtain protection from common diseases and start to develop an immune system. [2]

Colostrum is rich in several components including hormones, growth factors and antibodies. Many of these components support immunity and gut health, such as insulin-like growth factor, lysozymes, lactoperoxidase and lactoferrin. [5]

This first milk also contains high levels of vitamins and minerals, especially vitamin A.

Colostrum is also a source of oligosaccharides and essential fatty acids, which have been shown to promote gut development and improve thermoregulation (the ability to maintain a stable body temperature). [3][4]

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The antibody levels in colostrum are 100 times higher than in mature milk. These antibodies provide newborn foals with early protection from harmful bacteria and contagious diseases.

Immunoglobulins are the main antibodies in milk. They are large bioactive molecules composed of short and long polypeptide chains. The three most abundant types are:

  • immunoglobulin G (IgG)
  • immunoglobulin A (IgA)
  • immunoglobulin M (IgM)

Newborn foals have specialized cells in their digestive tract to accommodate these large molecules, allowing them to absorb the immunoglobulins in colostrum. [1]

Once absorbed, the immunoglobulins travel to the circulatory system and bind to foreign invaders, helping to destroy them. [2] Foals will encounter many new and potentially damaging pathogens as they mature and this immune transfer is vital to their survival.

Failure of Transfer

If a foal does not receive adequate immunoglobulins from her dam’s colostrum, this results in a failure of transfer of passive immunity.

These foals have low IgG levels in their blood and are more susceptible to harmful and potentially life-threatening diseases, such as: [2][7][8]

Composition of Colostrum

Compared to milk, colostrum is thick, sticky, and light yellow in colour. The consistency of a mare’s colostrum changes within 24 hours of giving birth as the mare transitions to making milk.

Over this initial 24-hour period, the protein content decreases and lactose content significantly increases. By three weeks post-partum, the mare’s milk composition is fairly stable and remains similar for the rest of the lactation. [6]

Table 1: Composition of equine colostrum and mature milk. [9]

Component Colostrum Milk
Fat 1.7% 1.2%
Protein 18% 1.7%
Lactose 1.5% 6.6%
Immunoglobulins* 27% 0

*Using brix refractometer

This table reflects the average composition of colostrum and milk. Colostrum composition could be affected by characteristics of the mare including: [9][10]

  • Breed
  • Parity
  • Diet
  • Season

Key Characteristics of Colostrum

To assess whether your foal is getting enough immunity transferred from her dam, we can evaluate the following characteristics of the dam’s colostrum:

  1. Quality
  2. Quickness of Delivery
  3. Quantity of Intake


Colostrum quality is determined by immunoglobulin content. This can be measured in the barn by assessing levels of IgG, which is the most abundant immunoglobulin.

IgG concentration is measured using a Brix refractometer – a small instrument that provides immediate results. A brix reading of 23% or above indicates good quality colostrum. [11]

Transfer of passive immunity to the foal can be assessed by testing the foal’s blood for serum IgG levels. This blood test is performed by your veterinarian.

Foals with IgG concentrations greater than 800 mg per 100 mL of blood have received adequate immunity. IgG levels below 400 mg per 100 ml indicate a failure of passive immunity. [2]


A vaccinated dam will transfer vaccine-related immunoglobulins to her foal through colostrum.

To optimize the transfer of vaccine-related antibodies transferred, it is recommended to vaccinate the mare one month prior to her due date. This allows adequate time for the mare to develop antibodies against the targeted pathogen and produce colostrum containing these specific antibodies. [2]

Several vaccines can be given to the mare to provide immunity to the foal. These include vaccines that protect against:

  • Rhodococcus Equi: Vaccination of broodmares reduces pneumonia in foals [12]
  • Clostridium difficile: Vaccination of the mare produces antibodies in colostrum that could protect against enterocolitis [13]
  • Equine herpesvirus 1: Vaccination of the mare increases antibodies in the foal that may protect against respiratory disease [14]

Consult with your veterinarian about which vaccines to give your gestating mare.


Foals should begin suckling as soon as possible after birth to ensure immunoglobulin absorption and immunity transfer. Most foals ingest colostrum within the first two hours after being born.

In the first 24 hours after birth, the foal’s gut barrier closes and the foal loses the ability to absorb large molecules, such as immunoglobulins, through the small intestine.

By 12 hours post-birth, the absorption rate is decreased by approximately 80%. [2]


Some foals are both with a weak suckle-swallow reflex, impairing their consumption of colostrum. This is known as dysphagia and it can be caused by cleft palate, muscle weakness, neurological disorders or trauma/injury. [15]

Signs of dysphagia include:

  • Milk in one or both nostrils
  • Coughing during or after ingesting milk
  • Drooling milk from the mouth

Monitor your foal closely within the first few hours. If the foal fails to consume colostrum, rapid intervention and veterinary care may be necessary.

Your veterinarian will assess your foal to determine the cause of dysphagia, hydration status, blood glucose levels, electrolyte balance, pain level and ability to regulate body temperature. [15]

Depending on this evaluation, your veterinarian will decide to provide nutrients into the gut via a nasogastric feeding tube or directly into the blood by IV infusion.


Foals need to consume enough colostrum to ensure they are getting adequate levels of immunoglobulins.

A foal should receive 2-3 L of colostrum within the first 6 to 8 hours of life over an average of 4 feedings. [4]

As they get older, healthy foals can consume as much as 27% of their body weight in milk daily, equivalent to 13 L for a 50 kg foal.

Sick foals may only tolerate 5-10% of their body weight in milk daily (equivalent to 2.5 – 5 L per day). This amount can be slowly increased as the foal recovers. [15]

Assessing Colostrum Intake

The quality of the dam’s colostrum, the timeliness of consumption (quickness) and the quantity that the foal consumes all affect the immunity and development of the newborn foal.

If any of the three Qs are suspected to be compromised, it is recommended to test the IgG concentration of the foal’s blood serum at 20 hours of age or later. [2]

Testing earlier will not accurately reflect the foal’s IgG levels due to the time required to absorb immunoglobins following colostrum consumption.

The most common causes of colostrum deprivation include: [16]

  • Premature birth
  • Delayed suckling
  • Death of the mare
  • Premature ejection of colostrum prior to foaling
  • Small intestinal malabsorption

If failure of transfer of passive immunity is identified, your veterinarian can recommend safe and effective ways to increase IgG concentration. Both oral and intravenous routes can be used to provide supplemental IgG. [17]

Feeding Orphaned Foals

A foal’s dam may not be able to provide colostrum in cases of illness, death or foal rejection.

In these cases, a suitable colostrum replacement should be used to promote immune system development.

Donor Colostrum

If you are caring for an orphaned foal, it may be possible to acquire colostrum from a donor mare or colostrum bank. At least 1 litre of colostrum should be given within 8 hours of birth. [18]

Up to 250 ml of colostrum can be collected from a donor mare at a single sampling time without reducing milk supply for her own foal.

Fostering the foal to another dam may also be a suitable option. Several organizations match foals with mares who have recently lost a foal to enable fostering. [19]

Equine Blood Plasma

If donor colostrum is not available, the best alternative is a transfusion of equine blood plasma rich in IgG. [20]

A blood transfusion from a donor horse will introduce IgG directly into the foal’s circulatory system, bypassing the need for intestinal absorption.

Transfusions must be given promptly or else the foal will remain susceptible to disease.

Frozen Equine Colostrum

If available, frozen equine colostrum is more cost-effective than equine plasma. Follow these management practices when using frozen colostrum:

  1. Test the quality of the colostrum before collection. A brix refractometer reading of 23% or above is suitable.
  2. Ensure collection of colostrum is sanitary. Clean your hands, the mares’ teats and the holding pail before milking.
  3. Thaw the frozen colostrum in a warm or hot water bath.
  4. Feed the colostrum from a bottle at a temperature of 38oC / 100oF to match the temperature of colostrum in the mare’s udder.

Be sure to test the foal’s serum IgG concentrations after the first day of life to assess the transfer of passive immunity.

Bovine Colostrum

Bovine colostrum (from cows) can be used as an alternative to equine colostrum. It is abundantly available and inexpensive.

Colostrum from cows is well-tolerated by foals and growth rates for foals consuming bovine and equine colostrum are similar. [21]

Antibodies in cow’s colostrum are well-absorbed by foals, but these antibodies appear to have a shorter half-life compared to antibodies found in equine colostrum.

Half-life is a way to measure how long a substance remains in the body before its level is reduced by half. Immunoglobulins from equine colostrum have a half-life of approximately 26 days whereas immunoglobulins from bovine colostrum have a half-life of approximately 7 days.

This means that foals given bovine colostrum may not be protected for as long as foals given equine colostrum, potentially increasing susceptibility to disease. The foal’s own production of immunoglobulins does not start until 40 – 50 days of age. [21]

In addition, cows might not be exposed to the same pathogens as mares so their colostrum may be lacking in specific antibodies that the foal needs.

Foals given bovine colostrum are at greater risk of diseases that are more common in horses than cows. For example, they have a higher risk of sepsis caused by Actinobacillus equuii, which is a common pathogen encountered by horses but not cows. [21]

Consult with your veterinarian about using bovine colostrum for your foal. Quality can vary greatly between batches. Be sure to keep it frozen and use it within 18 months. [21]

Milk Replacers

After the first day of life, an orphaned foal can be given equine milk replacers, which are specifically formulated to meet the foals’ nutritional needs.

It is not recommended to use other substitutes without consulting with your veterinarian.

Equine milk replacers should be given in small meals every 2 hours for the first two weeks of life. After two weeks have passed, gradually increase meal size and decrease feeding frequency.

Foals gain approximately 1 kg of body weight per day and milk intake must increase to support this growth. [4] By one month of age, a foal should be drinking once every 6 hours. [4]

Once an orphaned foal is weaned off milk, feeding will be less labour-intensive. Consult with your equine nutritionist to develop a feeding program to meet your foal’s nutritional requirements.

Feeding the Mare to Support Colostrum Quality

The mare needs a balanced diet during gestation and lactation to provide high-quality colostrum to her foal and to support sustained milk production.

Make sure that your mare’s weight and body condition are carefully managed during pregnancy. Both weight loss and excessive weight gain can affect the transfer of passive immunity and the health of the foal. [22]

Your mare’s feeding program must supply adequate energy and protein without over-supplying these macronutrients.

Energy requirements increase from 16.7 mcal per day in early gestation to 20 mcal per day in late gestation. Protein requirements increase from 630 grams per day in early gestation to 840 grams per day in late gestation. [23]

Consult with an equine nutritionist to design a feed program that supports appropriate weight gain while meeting the mare’s nutrient needs.

Vitamins and Minerals

In addition to providing appropriate calories to support weight gain and fetal growth, the mare’s diet must also supply vitamins and minerals to meet her needs and the needs of the growing foal.

Pregnant mares have a higher requirement for phosphorus, calcium, copper, iodine and vitamin E.

Vitamin E is an important antioxidant for both mare and foal. Mares supplemented with 160 IU of vitamin E per kg of feed produced colostrum with higher levels of IgG than those supplemented with 80 IU vitamin E per kg of feed.

Feeding mares 160 IU of vitamin E per kg of feed also resulted in foals with higher vitamin E status and higher circulating IgG. [24][31]

When supplementing your mare’s diet with minerals choose organic trace minerals, which are chelated and better absorbed and utilized by the body.

Foals born to mares supplemented with organic trace minerals had higher zinc and copper status compared to foals born to mares given inorganic trace minerals. [25]

Supplementing mares with organic selenium resulted in improved immune function in foals at 1 month of age, compared to supplementing with inorganic selenium. [26]

Mad Barn’s Omneity contains 100% organic trace minerals with adequate levels of zinc, copper, selenium and vitamin E to meet the needs of broodmares.

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Additional supplements, such as probiotics, have been shown to improve colostrum quality and the transfer of passive immunity.

Supplementing with live cultures of yeast and bacteria supports the mare’s digestive tract and can influence colostrum quality. In several studies, foals born to mares supplemented with yeast during pregnancy and lactation were found to:

  • Have higher levels of certain types of IgG by 60 days of age [27]
  • Greater absorption and retention of nutrients from the milk [28]
  • Benefit from higher milk production by their dam [28]

Mad Barn’s Optimum Digestive Health contains high levels of yeast, prebiotics and probiotics to support hindgut function. Supplementing mares will support fibre digestion in the hindgut and can support increased milk production and immunoglobulin supply to the foal.

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Docosahexaenoic acid (DHA) is an omega-3 fatty acid found only in marine sources, such as fish oil or algae. It has greater anti-inflammatory effects compared to plant-derived omega-3 fatty acids, such as arachidonic acid (ALA) from flax or camelina oil.

Supplementing DHA during late gestation and early lactation has been shown to improve social behaviour prior to weaning and memory and learning at two years of age. Reproductive health is also improved in broodmares given DHA as seen by faster uterine involution after parturition (birth). [30]

Studies show that supplementing the pregnant mare with microalgal increases the foal’s plasma DHA. Supplementing with plant-based omega-3’s from flax oil does not affect the mare or foal’s circulating DHA and will not provide the same benefits. [29]

Mad Barn’s w-3 oil contains microalgal DHA to provide anti-inflammatory benefits to the mare and foal. It also contains high levels of natural vitamin E for antioxidant support.

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  2. Watt, B. and Wright, B. The importance of Colostrum to Foals. Equine Guelph. 2008.
  3. Blum, J. and Hammon, H. Colostrum effects on the gastrointestinal tract, and on nutritional, endocine and metabolic parameters in neonatal calves. Livest Prod Sci. 2000.
  4. Fischer-Tlustos, A.J. et al. Oligosaccharide concentration in colostrum, transition milk, and mature milk of primi- and multiparous Holstein cows during the first week of lactation. J Dairy Sci. 2020.
  5. Pakkanen, R. and Alto, J. Growth factors and antimicrobial factors of bovine colostrum. Intern Dairy J. 1997.
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  7. Nervo, T. et al. Analysis of factors influencing the transfer of passive immunity in the donkey foal. Ital J Anim Sci. 2021.
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  9. Barreto, I.M.L.G. et al. Chemical composition and lipid profile of mare colostrum and milk of the quarter horse breed. PLoS One. 2020. View Summary
  10. Markiewicz-Kexzycka, M. et al. Influence of stage of lactation and year season on composition of mares’ colostrum and milk and method and time of storage on vitamin C content in mares’ milk. J Sci Food Agric. 2015. View Summary
  11. Schneider, F. and Wehrend, A. Quality Assessment of Bovine and Equine Colostrum – An Overview. Schweizer Archiv fur Tierheilkunde. 2019. View Summary
  12. Cauchard, J. et al. Foal IgG opsonizing anti-Rhodococcus equi antibodies after immunization of pregnant mares with a protective VapA candidate vaccine. Vet Microbiol. 2004.
  13. Artiushin, S. et al. Immunisation of mares with binding domains of toxins A and B of Clostridium difficile elicits serum and colostral antibodies that block toxin binding. Equine Vet J. 2013. View Summary
  14. Sasa, L. Presence of main serum protein fraction content, immunoglobulin G and titers of antibodies against herpesvirus 1 in newborn foals originating from vaccinated and unvaccinated mares. University of Belgrade. 2013.
  15. Buechner-Maxwell, V. Practical Approach to Nutritional Support of the Dysphagic Foal. AAEP. 2012.
  16. Frape, D. Feeding the Breeding Mare, Foal and Stallion. Equine Nutrition and Feeding. 2013.
  17. Franz, L.C. et al. Oral and intravenous immunoglobulin therapy in neonatal foals. J Equine Vet Sci. 1998.
  18. Zurek, U. and Danek, J. Foal Rejection – Characteristics and Therapy of Inadequate Maternal Behaviour in Mares. Annals of Anim Sci. 2012.
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  20. Leblanc, M.M. and Pritchard, E.L. Effects of bovine colostrum, foal serum immunoglobulin concentration and intravenous plasma transfusion on chemiluminescence response of foal neutrophils. Anim Genet. 1988. View Summary
  21. Leblanc, M.M. Is bovine colostrum a suitable alternative source of immunoglobulins for newborn foals?. Equine Vet J. 1991.
  22. Peugnet, P. et al. Management of the pregnant mare and long-term consequences on the offspring. Theriogen. 2016.View Summary
  23. National Research Council Nutrient Requirements of Horses. NRC. 2007.
  24. Kane, E.D. Vitamin E: An essential nutrient for horses? Advances in Equine Nutrition IV. 2009.
  25. Ott, E.A. and Asquith, R.L. Trace Mineral supplementation of broodmares. J Equine Vet Sci. 1994.
  26. Montgomery, J.B. et al. The Effects of Selenium Source on Measures of Selenium Status of Mares and Selenium Status and Immune Function of Their Foals. J Equine Vet Sci. 2012.
  27. Leimbach, R. Influence of a Maternal Dietary Yeast Supplement on Immunoglobulin Concentrations in Quarter Horse Foals from Birth to Four Months of Age. Ohio State University. 2015.
  28. Glade, M.J. Effects of dietary yeast culture supplementation of lactating mares on the digestibility and retention of the nutrients delivered to nursing foals via milk. J Equine Vet Sci. 1991.
  29. Snyder, E.A. Evaluating Sources Of Omega-3 Fatty Acids For Their Benefits On Late Gestation Mares And Neonatal Foals. Sam Houston State University. 2020.
  30. Chavette-Palmer, P. and Robles, M. Developmental programming: Can nutrition of the mare influence the foal’s health? CBRA. 2019.
  31. Bondo, T. and Jensen, S.K. Administration of RRR-?-tocopherol to pregnant mares stimulates maternal IgG and IgM production in colostrum and enhances vitamin E and IgM status in foals.Journal of animal physiology and animal nutrition. 2010.View Summary