Sepsis is an extreme systemic inflammatory response which develops when a foal becomes infiltrated with bacteria and infection spreads unchecked through its body. The most common bacteria seen in septic foals (about 60 to 70 per cent of cases) are E. coli; others often identified include klebsiella and actinobacillus. Cases with enterobacter, salmonella, pseudomonas and streptococcus have also been seen. The bacteria can enter the foal’s body through the placenta, at the umbilicus, or through the nose or mouth.

The foals at greatest risk are those which don’t receive the antibody-rich first milk (colostrum) from their dams. Foals are born with the ability to develop antibodies, but without any already present, they are vulnerable to infections. The colostrum contains high levels of antibodies to the bacteria that the mare has been exposed to, so those early feedings are extremely important.

In most cases, the foal nurses soon after birth and the protective antibodies can soon be detected in his bloodstream. Occasionally, however, something goes wrong. Perhaps the mare does not, for some reason, have a high enough level of antibodies in her colostrum. She might not lactate at all, or she might produce colostrum too early – before the foal is born – and those vital antibodies are lost as she leaks milk. The problem may also be with the foal: he might be born a bit early and be too weak to nurse right away, or he might have some physical problems that prevent him from feeding. For example, a foal born with contracted tendons is unable to stand to nurse and subsequently may be at risk of developing sepsis.

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