Thick, sticky, yellowish fluid secreted by the mare’s mammary gland around the time of birth. Colostrum is loaded with protein, fat, and sugars as well as minerals and particularly immunoglobulins vital to providing immunity to the newborn foal.
In horses, immunity is not transferred from mare to foal before birth – the immunoglobulin molecules are too big to cross the placental barrier. Instead, they are transferred in colostrum immediately after the foal is born. The small intestine of foals is permeable to colostral antibodies for only the first 12- 24 hours of life so there is a short window of time during which colostrum can be effective in providing immunity.
This passive immunity from the dam will help protect the foal from bacterial and viral infections for the first 6-12 weeks by which time its own immune system will be able to take over. Newborn foals should consume 2-4 liters of colostrum as soon as possible after birth. The transfer of immunity can be assessed by use of an IgG test on a foal blood sample, preferably within the first 24 hours of life. Where immune transfer has failed and the foal’s immunoglobulin levels are low, a plasma transfusion may be recommended by the attending veterinarian to boost immunity.
A good dose of colostrum in the first few hours after birth is the best possible start in life the foal can have whereas the lack of it can have dire consequences laying the foal wide open to a range of potentially serious infections.