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 defences. 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. 
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. 
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. 
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). 
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. 
Once absorbed, the immunoglobulins travel to the circulatory system and bind to foreign invaders, helping to destroy them.  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.
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. 
Table 1: Composition of equine colostrum and mature milk. 
*Using brix refractometer
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:
- Quickness of Delivery
- 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. 
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. 
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. 
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 
- Clostridium difficile: Vaccination of the mare produces antibodies in colostrum that could protect against enterocolitis 
- Equine herpesvirus 1: Vaccination of the mare increases antibodies in the foal that may protect against respiratory disease 
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%. 
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. 
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. 
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. 
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. 
Assessing Colostrum Intake
The quality of the dam’s colostrum, the t