Colostrum is the first milk secretion produced by the mare immediately post foaling. Its' appearance should be opaque, yellow, thick and sticky. Normal colostrum contains high levels of antibodiesspecifically known as IgG, IgM and IgA, the greatest quantity being IgG. These antibodies are very important because they aid in protecting the foal against infections. Infections occurring after birth (parturition) are most likely due to inadequate colostral antibody transfer from the mare to the foal.

The foal is born immunocompetent, (it has an immune system). However, the foal's immune system is not completely functional at birth. It is slow to respond to and has low antibody production against infection, therefore it is quickly overwhelmed by bacteria found in the normal environment. Unlike many other animal species where the mother can transfer these all important antibodies to its fetus(es) in utero through circulation, this does not occur in the horse. This is because the mare's placenta is thicker than other animals, effectively separating the maternal and fetal circulation. Thus, there is no transfer of maternal antibodies to the fetus in utero and the foal is born without circulating IgG.

Protection against infections, or at least a fighting chance, occurs when the foal nurses and thus ingests colostrum enriched with the infection fighting IgG antibodies. This is known as Passive Transfer of antibodies.

Colostral antibodies are absorbed through the foal's GI tract, specifically the intestines. Failure to get sufficient amounts of antibodies can lead to serious consequences such as septicemia, multiple localized infections or death. This inadequate transfer of antibodies is known as partial or complete Failure of Passive Transfer (FPT).

Absorption of antibodies through the foal's GI system occurs for the first 24 hours of life, however, the peak absorption time appears to be within the first 8 hours after birth. If your foal hasn't received colostrum by the first 12 hours of life it may be too late to use this mode of antibody transfer. Some of the reasons FPT occurs include;

  • failure of the mare to produce antibody-rich colostrum,
  • premature lactation (the mare drips milk before giving birth)
  • the foal fails to nurse or the foal nurses and does not absorb the antibodies. A foal that ingests 1 to 2 liters of good quality colostrum should have an antibody level of 800 - 1000 mg/dL.