To a newborn foal, colostrum can mean the difference between life and death. | Photo: Anne M. Eberhardt/The Horse

Now that foaling season is here, equine veterinarians who routinely treat and care for foals will be thinking about colostrum—who has it, who needs it, and where they can get it. You might wonder if colostrum actually is that important. To a newborn foal, it can mean the difference between life and death.

To discuss why colostrum is so important, I first have to explain about the precarious situation into which a foal is born. We all know that to fight infection, healthy people and horses have a functioning immune system that can mount a response, in the form of specialized cells that kill invading bacteria. The foal is born with an immune system that is intact, but is not born with any circulating (within the bloodstream) antibodies that can fight infection.

The foal isn’t born with antibodies derived from the dam’s bloodstream as is the case with humans. The foal, while in the uterus, has a bloodstream that is separated from the dam’s bloodstream by the placenta, which in the horse has six layers. These layers do not allow particles as large as immunoglobulins (antibodies) to cross, so the foal cannot derive antibodies from the mare and is born with little to no circulating