Infectious diarrhea in young foals can be fatal without prompt treatment, and the age of the foal can make a difference in his vulnerability to certain pathogens and how deadly they might be. In foals less than a week old, the cause is often salmonella or a clostridium bacteria.

Sam Jones, DVM, PhD, Dipl. ACVIM, associate professor of equine medicine at North Carolina State University, says diarrhea might also appear in foals that are septic (have infection in their bloodstreams) from other bacteria. They can get a blood infection from navel ill or bacteria that go through the gut lining soon after birth, and the resulting systemic infection creates diarrhea along with all the other signs.

During the first 24 hours of life, the foal has a very open gut that can absorb large molecules (to allow for absorption of antibodies from colostrum). If the foal ingests bacteria, they can also be transferred across to the bloodstream, explains Jones.

“If a mare has a dirty udder or the environment is dirty, the foal picks up a lot of bacteria,” he says. “It is very important that the foal get adequate amounts of colostrum because it gives local protection within the gut as well as in the bloodstream