It is 9:40 PM, and Class On Class’ water breaks. Her new filly arrives at 10:00 PM, stands up at 10:38 PM, and nurses for the first time at 11:18 PM. After a normal delivery and an exciting, successful attempt to stand, the one hour and eighteen minute old filly receives the most important milk her mother will ever produce: colostrum.
At 11:18PM, after receiving colostrum, this filly’s immune system will be able to fight infection for the first sixty days of her life. Foals receive no transfer of immunity through the placenta before birth, so antibodies need to be ingested. After this period, her own immune system will be developed enough to offer sufficient protection.
Colostrum is the first milk produced by a mare. With the consistency of honey, it is thick and yellow and very different to the thin, white milk she will produce subsequently. Antibodies from the mare’s blood are collected in the mammary glands and contained within the colostrum that will transfer to the foal after its first nursing.
When a foal successfully receives colostrum through nursing, it is called “Passive Transfer.” A foal’s digestive system can only break down and utilize the colostrum in the first 24 hours of life, with the most effective absorption between 6 and 8 hours from birth.
After a foal is born, a veterinarian performs an initial exam and blood is drawn so that an IgG test can be taken. An IgG test determines the amount of Immunoglobulin G, the most common antibody, that has been absorbed into the foal’s bloodstream.
Amounts greater than 400 mg to 800 mg are considered sufficient levels. If a foal does not absorb enough colostrum from the mare and has levels less than 800 mg, it is known as “Failure of Passive Transfer.” In this scenario, supplementation is required. Recording the time of nursing is an important factor in knowing how much time there is to effectively supplement after the IgG test results are displayed.
There are three possible causes for failure of passive transfer: the mare produces low-quality colostrum, she dripped the milk prior to the foal being born, or the foal does not nurse.
The quality of colostrum is typically lower in maiden mares, but it can be low at any stage of a broodmare’s career. Looking for the sticky, thick, and yellow milk at the udder is an easy way to determine if colostrum is present. The presence of this prior to foaling is known as “waxing up” and is also an indication of imminent foaling. Additionally, a tool called a colostrometer is used to measure the specific gravity (the ratio of the density of colostrum to the density of water) and give an estimate of the IgG content. A refractometer may be used in place of a colostrometer to measure the amount of IgG in a colostrum sample.
All mares will drip milk before giving birth, but some will have excessive dripping. In these cases, colostrum may be depleted or absent by the time the foal is born. If a foal is unable to stand on its own, it will be unable to nurse.
There is one situation in which the foal is not allowed to nurse from their mother at all; when there is a risk of neonatal isoerythrolysis (NI).
NI is a disease that causes a low red blood cell count in the foal, also known as anemia. This occurs when their mother produces antibodies after exposure to specific foreign red blood cells (antigens) and they are included in the colostrum. The mare can be exposed to these antigens through a blood transfusion or from a previous foal’s blood during foaling.
Since the foal may have the specific red blood cell antigen inherited from the sire, ingesting the mare’s colostrum containing the red blood cell antibodies can prove fatal if not discovered quickly. The red blood cell antibodies from the mare will attack the red blood cell antigens in the foal. Once a mare is found to be NI positive, the foal is muzzled to prevent nursing, and colostrum from another mare is needed immediately. Once the colostrum has been milked from the NI positive mare, the foal may nurse as normal from its mother.
Without the immunity received from colostrum, a foal is susceptible to a host of bacteria and viruses. Since colostrum is essential to the health of a foal and needs to be supplemented in some cases, many farms and veterinary practices have “colostrum banks.”
From a healthy mare without a history of dripping milk, up to 20 ounces can be collected without impacting the amount necessary for her own foal. The mare is milked by hand, and the colostrum is then frozen and kept in a bank for up to two years.
At Stonestreet, we maintain our own colostrum bank. Both Hagyard Equine Medical Institute and Rood and Riddle Equine Hospital have colostrum banks that are supplied by donations. We donate to these banks once our own supplies are sufficient to provide for the Stonestreet foals.