Colostrum is the first milk produced by female mammals, including mares, immediately after giving birth. It is a thick, yellowish fluid that is rich in essential nutrients, growth factors, antibodies known as immunoglobulins, and other immune-boosting substances.

Mares only produce small quantities of colostrum, but this highly concentrated substance is essential for the health of foals during their early days of life. Colostrum builds the foal’s immune system, provides nutrients for growth and development, and promotes development of the gut. [1]

Newborn foals must consume sufficient colostrum within the first few hours after birth to absorb vital antibodies. During this period the foal’s gut is permeable, allowing immunoglobulins in colostrum to pass directly into the bloodstream.

However, the quantity, quality and antibody content of colostrum can vary among mares. Some mares may produce colostrum that lacks sufficient antibodies to adequately protect the foal. Other foals may not be able to nurse their mare for various reasons including illness or loss of the mare, rejection by the mare, or prematurity of the foal. [1]

In such cases, donor colostrum ensures that a foal receives necessary immune support, even if colostrum is insufficient or unavailable from its mother. Breeders can collect and store their own donor colostrum or use the services of a colostrum bank. [4]

Colostrum for Foals

During late pregnancy and in the immediate hours following foaling, the mare’s mammary glands produce a thick, golden-yellow fluid called colostrum. This first milk is rich in specialized proteins called immunoglobulins, which help to establish the immune system of the newborn foal. [1]

In the initial hours after birth, a foal’s mother gradually shifts from producing colostrum to mature milk. Mare’s milk has a distinct nutritional composition with lower antibody levels compared to colostrum. [1]

Newborn foals must consume enough colostrum within the first 24 hours of life, as this is when their gastrointestinal tract is most permeable to the large immunoglobulin molecules.

After this period, the foal’s intestines undergo gut closure, significantly reducing the foal’s ability to absorb these antibodies into the bloodstream. [1]


The concentrations of antibodies in colostrum are 100 times greater than those in mature milk. These antibodies, or immunoglobulins, provide newborn foals with early protection from harmful bacteria and contagious diseases.

Immunoglobulins are large bioactive protein molecules that are produced by white blood cells in the horse’s body. They recognize and bind to antigens, such as bacteria and viruses, and trigger an immune responses that help to neutralize or eliminate invading pathogens from the body. [1]

The immunoglobulins found in colostrum mainly consist of these three types:

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

Immunoglobulin G (IgG) is the most prevalent antibody, accounting for over 80% of immunoglobulins in the horse’s colostrum and blood. [5]

Newborn foals have special cells in their digestive tract that enables them to absorb the immunoglobulins in colostrum. [6][7] Once immunoglobulins are absorbed, they travel through the bloodstream and aid the immune system in identifying and destroying pathogens. [1]

This is particularly important for foals because they are born with an immature immune system. Newborn foals rely on the passive transfer of immunity from the mare through colostrum to protect them during the early stages of life when they are most vulnerable to infections.

Other Components

In addition to antibodies, colostrum is also rich in nutrients such as proteins, fats, sugars, vitamins, and minerals. These nutrients supports the initial growth and energy requirements of the foal.

Colostrum is also a source of hormones, growth factors, enzymes, white blood cells, and antimicrobial factors, which play various roles in the foal’s early development and immune function.

Besides providing passive immunity, colostrum contains factors that promote the maturation of the foal’s gastrointestinal tract. These factors promote gut closure, preventing the absorption of large molecules and pathogens that could harm the foal. [6]

Components in colostrum that support immunity and gut health include the following: [8][9][10]

  • Insulin-like growth factor
  • Lysozymes
  • Lactoperoxidase
  • Lactoferrin
  • Oligosaccharides
  • Essential fatty acids
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Does your Foal need Donor Colostrum?

Newborn foal should consume two to three liters of colostrum within the first six to eight hours of life, over an average of four feedings. [1]

If your foal does not get enough colostrum from their dam, they should be given donor colostrum, ideally within the first 12 hours of life when immunoglobulin absorption is highest.

It is important to monitor the foal’s feeding ability and the mare’s health and behaviour during the first few hours after birth to determine if intervention is necessary.

Early detection of nursing issues is crucial to promptly provide the foal with donor colostrum, support passive immunity, and supply the foal with essential nutrients. [4]

Observing the Newborn Foal

The American Association of Equine Practitioners (AAEP) outlines the 1-2-3 rule for monitoring a newborn foal after birth. According to this rule, a newborn foal should be: [3]

  • Standing within one hour
  • Nursing within two hours
  • Passing meconium (first feces) within three hours

Healthy foals are expected to stand within one hour after parturition (birth), and begin actively seeking the mare’s udder. By two hours after birth, the foal should begin suckling. Once the foal has found the udder, a healthy foal will nurse every 30 minutes. [2][3]

If a foal is not suckling within two hours after birth, this could indicate potential health issues requiring immediate veterinary attention. Poor suckling can also lead to low colostrum intake, which may necessitate the use of donor colostrum.

Reasons for Abnormal Suckling

There are several reasons a foal may not nurse adequately in the first day of life, including:

  • Prematurity: Foals born prior to 320 days of gestation may be too weak or underdeveloped to nurse.
  • Birth Asphyxia: Any difficultly during delivery that results in asphyxia (low oxygen supply) to the foal can impact neurological function.
  • Neurological Issues: Illnesses or conditions, such as dummy foal syndrome, can impair the foal’s ability to nurse.
  • Conformation issues: Limb conformation defects can make it difficult for the foal to stand and nurse.
  • Birth defects: Physical abnormalities, congenital defects or genetic diseases can impair the ability to suckle.

If you suspect your foal has a significant impairment contact your veterinarian immediately. While awaiting your veterinarian, focus on preventing hypothermia in your foal by keeping them in a warm area. You can also support proper breathing by helping them lie in an upright position. [3]

Your veterinarian will perform a thorough assessment to determine how best to support the foal, which may or may not include feeding donor colostrum.

Observing the Mare

Several factors, both behavioral and physiological, can contribute to a mare not producing sufficient colostrum for her foal. Mare behaviours can also interfere with the foal’s ability to nurse, even if colostrum production is adequate.

Insufficient Colostrum Production

A mare may have insufficient colostrum production due to various reasons:

  • Premature Delivery: The foal is born before normal colostrum production begins.
  • Premature Lactation: The mare loses colostrum out of the udder prior to foaling and is already producing mature milk when the foal arrives.
  • Illness: The mare is sick and does not produce enogh colostrum.
  • Multiple Foals: The mare gives birth to twins and does not produce enough colostrum to adequately supply both foals.
  • Nutritional Deficits: A diet lacking in key nutrients during pregnancy can impact colostrum quality and volume.
  • Genetic Factors: Some mares may naturally produce less colostrum due to genetic predispositions.
  • Mastitis: Infection or inflammation of the mammary glands, known as mastitis, can severely affect colostrum quality and quantity.
  • Age and Previous Births: Both older mares and young, first-time mothers may struggle with colostrum production.

In some cases, a mare may produce sufficient colostrum that is consumed readily by a healthy foal. However, if the colostrum has low antibody content the foal can still be at risk of failed passive transfer and require donor colostrum.

Ensuring that a broodmare receives optimal nutrition throughout her pregnancy is critical for her to produce colostrum of sufficient volume and quality. [17]

Closely monitor the mare throughout her pregnancy and promptly address any health concerns. As she nears her expected foaling date, pay special attention to changes in her udder, which can indicate readiness for colostrum and milk production.

Consult with your veterinarian if you notice signs that the mare is not adequately preparing for lactation. If you observe colostrum dripping from the teats prior to foaling, the foal will likely need donor colostrum.

If the mare is too ill to nurse, or if she dies during or shortly after birth, donor colostrum is essential to provide the foal with necessary immunity and nutrients.

Mare Behavioural Issues

Mares typically exhibit a strong maternal instinct, which drives them to protect and bond with their newborn foals. Part of this instinctual behavior includes encouraging the foal to nurse effectively.

However, some mares may engage in behaviours that hinder the foal’s ability to nurse and acquire colostrum. The six most common mare behaviours that can impact nursing are: [11]

  • Ambivalence: The mare is uninterested in bonding and may not allow nursing, typically observed when the mare and/or foal are sick.
  • Fear of the Foal: The dam acts as if the foal is a threat and prevents the foal from nursing, typically seen in first-time dams.
  • Overprotection: The dam over-reacts to real or perceived threats and may accidently injure her foal, particularly when in a confined space such as a stall.
  • Nursing-Only Avoidance: The mare doesn’t allow nursing despite other bonding behaviours being normal, typically associated with pain or discomfort in the dam.
  • Savage Attack: True foal rejection where the mare aggressively attacks the foal, often causing life-threatening injuries or death.
  • Stealing the Foal: Another mare steals the foal away from the dam.

During the first few hours after foaling, mares should be monitored for any behaviour that prevents the foal from nursing. In extreme cases, such as aggressive foal rejection, the pair must be separated to protect the foal. [11][14]

In other cases, the foal may require donor colostrum for the first day of life to ensure they receive immunity while still allowing opportunities for the mare and foal to bond.

Keep in mind that it is normal for the mare to step away from the foal when it is first searching for the udder. This is not usually a sign of rejection. Instead, it is believed to be an instinctive behavior designed to teach the foal to follow the mare. [11]

Donor Colostrum for Foals

Donor colostrum can be a lifesaver in situations where a foal fails to receive an adequate amount of colostrum within the first few hours of life. Donor colostrum is often obtained from mares that have produced an excess of colostrum beyond what their own foals require, from established colostrum banks, or from other mares in the same herd.

The key is to ensure that the donor colostrum has sufficient IgG content and is administered to the foal within the first 12 hours after birth for maximum benefit.

Sources of Donor Colostrum

If your newborn foal needs donor colostrum, you only have a short period of time to act, since its absorption diminishes significantly after 24 hours. It’s a good idea to research sources of donor colostrum in your area prior to your mare’s predicted foaling date.

Some veterinary clinics may keep a supply of donor colostrum or can recommend sources. Your veterinarian can also guide you on the best practices for colostrum collection and storage.

The Healthy Dam

In some cases, the dam produces a sufficient volume of colostrum but the foal is unable to nurse independently. The mare’s colostrum can be manually expressed and then fed to the foal, usually via a bottle or a nasogastric tube, depending on the foal’s condition and ability to suckle.

The mare should be milked at least every 2 – 3 hours to maintain adequate milk production until the foal is able to nurse by itself. [2]

Foster Mares

You may be able to unite a healthy foal with a foster mare who has lost their own foal to provide donor colostrum. In this scenario, the foal directly nurses from the foster mare, receiving not only colostrum but also the benefits of a mare-foal relationship. This includes protection, social support, and ongoing nutrition, which are crucial for the foal’s development.

In certain regions, professional nurse mare services are available for lease. These services come with expertise in ensuring acceptance of the foal. [11]

Other Early Lactation Mares

Large breeding operations may have multiple mares foaling per day, providing a potential source of fresh donor colostrum for the foal.

When selecting a donor mare, prioritize these traits to ensure high-quality and abundant supply of colostrum: [1][15][16]

  • Mares that have had had one or more foals previously
  • Mares that are between 4 – 15 years of age
  • Mares that have not dripped colostrum prior to foaling
  • Mares that are up-to-date on vaccines
  • Mares that have not previously birthed foals that developed neonatal isoerythrolysis (NI or jaundice foal syndrome)

Personal Stored Supply

You can establish your own supply of frozen colostrum by collecting first milk from one or more healthy mares and storing it appropriately.

Collecting a small volume (8 to 16 ounces) of high-quality colostrum from nursing mares is unlikely to impact the passive transfer of immunity to their own foals. [16]

Colostrum Banks

Some veterinary clinics or pharmacies operate colostrum banks, providing access to stored colostrum. These facilities also test the colostrum to guarantee its high quality.

Consult with your veterinarian to learn about colostrum banks in your area. Examples of commercial colostrum banks in the United States include:

Collecting and Storing Colostrum

Whether you’re collecting colostrum to feed directly to a foal, store on your farm, or donate to a colostrum bank, the process remains the same.

The main objective is to collect colostrum that is clean and free from any debris, and to store it appropriately for future use.

How to Collect Colostrum

Colostrum should be collected within two hours following delivery. Immunoglobulin content declines rapidly after birth, with one study showing a 70% drop in IgG content by 7 hours post-parturition. [2]

If the mare is also nursing a foal, collect from the teat opposite of where the foal is suckling. Nursing by the foal will stimulate the mare’s natural letdown reflex, enabling colostrum collection. Mare that do not have a nursing foal may require an oxytocin injection to activate milk letdown. [2]

Follow these five steps to collect clean colostrum: [16]

  1. Gently wash the udder using warm water and mild soap.
  2. Wipe the teat thoroughly with an alcohol swab for disinfection.
  3. Ensure your hands and all equipment used are cleaned and sanitized.
  4. Discard to first secretions to avoid collecting microbes or debris.
  5. Collect the colostrum using hand milking, a syringe or commercial milking machine.

Collection Methods

To collect colostrum, you have several options, each with its own advantages:

Hand Milking:

  • This method involves gently squeezing the mare’s teat to force the milk downward within the teat canal using clean hands.
  • The colostrum is expressed directly into a clean vessel, such as a measuring cup.
  • Hand milking is ideal for small-scale needs and doesn’t require specialized equipment.

Inverted Syringe:

  • This method involves using a large 60 mL syringe (minus the needle) to draw colostrum from the teat.
  • The syringe method can reduce the risk of contamination and is relatively easy to perform.

Commercial Milking Machine:

  • Designed for larger-scale colostrum collection, these machines can efficiently milk mares.
  • These machines are expensive and require training, but are more typical on breeding farms or for colostrum banks.

Collection Volume

The collected colostrum should be strained through a clean cotton gauze or cheesecloth into a storage container that can be sealed and placed in the freezer.

A total of 8 – 16 ounces (240 – 475 ml) can be collected from a mare without affecting her own foal’s colostrum supply. [16]

Colostrum Storage

Ideally, colostrum should be stored in a sealed plastic container. Glass bottles should be avoided as they may break as the liquid freezes. Similarly, avoid using thin plastic bags which can rip easily. [16]

Label the container with the mare’s name, date of collection, colostrum quality measurement, and NI status (if tested). [16] If small volumes are collected from multiple mares, the samples can be combined and stored for future use.

Freeze the colostrum at -20° C (-4° F) to ensure optimal stability and preservation of the antibodies and nutrients. Frozen colostrum can be stored for up to two years. [16]

Testing Colostrum Quality

Testing the quality of colostrum is important to ensure that it contains adequate levels of antibodies to confer passive transfer. This is accomplished by measuring the immunoglobulin G (IgG) content of stored colostrum.

Colostral IgG levels can be measured on-farm using a Brix refractometer. This is a small instrument that measures the refractive index of a liquid, which correlates with colostrum quality. [12]

Only keep colostrum with a Brix reading of 23% or higher. [12] Colostrum with lower IgG levels is unlikely to provide enough antibodies to the foal.

Ideally, the colostrum should undergo further testing for the presence of antibodies against red blood cells. [16] This precaution helps prevent a condition known as neonatal isoerythrolysis (NI) in foals that receive stored colostrum. [16]

Feeding Donor Colostrum

To feed frozen colostrum it must be thawed gradually to room temperature. Allow the container to thaw at room temperature or use a warm water bath set to 100° F (38° C). [16]

Ensure that the temperature of the colostrum does not exceed 110° F (43° C) to avoid damaging the antibodies. Also avoid using a microwave, as the high temperatures can denature proteins and reduce the immunoglobulin content. [16]

How to Feed Donor Colostrum

Donor colostrum should be provided within the first few hours of life to support transfer of immunity to the foal.

If the foal is able to suckle, transfer the thawed colostrum into a sanitized plastic feeding bottle. If the situation allows, you can support a healthy mare-foal bond and encourage future natural feeding behaviour by holding the feeding bottle near the mare’s udder.

If the foal is unable to suckle and your veterinarian has deemed it safe to do so, the colostrum can be administered via a nasogastric tube. This is a feeding tube that is passed through the nose into the stomach to directly deliver the colostrum.

A typical feeding protocol involves administering 300 – 500 ml (10 – 17 ounces) of colostrum between 1 – 4 times within the first six hours after birth. Follow this with continued feedings every two hours for the first 24 hours of life. [20]

Keep the mare and foal together as much as possible with minimal intervention. This will reduce stress in both the mare and foal and encourage natural bonding. [11]

Assessing Transfer of Passive Immunity

To assess if a foal has received adequate colostrum and has successful transfer of passive immunity, a veterinarian will check the foal’s blood IgG levels This test is typically performance around 24 hours after birth.

  • Adequate Transfer: IgG levels above 8 g/L indicate successful immunity transfer, suggesting the foal is well-protected against pathogens the mare has antibodies for.
  • Partial Transfer: IgG levels between 4 and 8 g/L suggest partial immunity transfer. These foals might be more vulnerable to infections and require close monitoring.
  • Failed Transfer: IgG levels below 4 g/L indicate failed passive transfer, placing the foal at a high risk of infectious diseases.

Failed passive transfer is fairly common, occurring in up to 18% of foals. [20] IgG testing should be part of routine veterinary exams for all newborn foals, whether they receive donor colostrum or not.

Managing Failed Passive Transfer

Foals with failed passive transfer are highly susceptible to illness due to inadequate antibody levels. By the time blood IgG levels are measured, it is too late to provide more colostrum because gut closure will already have occurred. The foal will no longer be able to absorb antibodies from colostrum.

The alternative for these foals is a direct blood infusion of plasma containing antibodies. This procedure increases immunoglobulin levels in the foal, but is more effective in healthy foals than those that are ill. [18]

Your veterinarian may collect plasma antibodies from a healthy donor or use commercially available hyperimmune plasma. After plasma infusion, the foal should be closely monitored for signs of allergic reaction.

If plasma is unavailable, foals with failed passive transfer need vigilant monitoring for signs of illness. Immediate veterinary intervention with antibiotics and supportive care is critical to support their recovery.

Bovine Colostrum

If donor colostrum from a horse is not available, your veterinarian may recommend using bovine colostrum. [13] Colostrum from cows is abundantly available and cost-effective.

Studies show that foals tolerate bovine colostrum well and its use does not negatively impact their future growth or performance. [19] However, cow colostrum may lack antibodies against common equine pathogens, as cows are exposed to different illnesses than horses.

In addition, cow antibodies have a shorter half-life in the foal’s blood. This means the antibodies will disappear more quickly than horse antibodies, leaving the foal at risk of disease. [19]


  • Colostrum is the first milk produced by a mare after foaling. It is rich in antibodies (immunoglobulins) that protect the foal against harmful bacteria and diseases.
  • A foal must consume sufficient high-quality colostrum in the first day of life to have successful passive transfer of immunity.
  • Several scenarios may result in the foal not getting enough colostrum from their dam, requiring the use of donor colostrum.
  • Donor colostrum should be collected under sanitary conditions and frozen for future use. It should be tested for its IgG content and for the presence of certain antibodies that may cause illness in the foal.
  • If donor colostrum is not available, your veterinarian may administer a blood infusion of antibodies or suggest feeding colostrum from cows.
  • All foals should have their blood IgG levels measured around 24 hours after birth to confirm successful passive transfer of immunity.

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