Septicemia is a condition in which bacteria or their toxins are circulating in the bloodstream and triggering a systemic inflammatory response. In horses, the term is applied most commonly to neonatal newborn foals, for whom it is one of the leading causes of early death. The neonatal foal is born with a naive immune system and depends entirely on absorbing immunoglobulins from the mare’s colostrum in the first 12 to 24 hours of life. When that transfer fails — whether because colostrum was inadequate, not consumed in time, or the foal did not absorb it — the foal is left without antibody protection, and bacteria that would be contained by a functional immune system proliferate freely in the blood.
Common causative organisms in foal septicemia include Actinobacillus equuli, Escherichia coli, Klebsiella, and Salmonella. Clinical signs — depression, failure to nurse, weak suck reflex, fever, joint swelling, or diarrhea — can appear within 12 to 48 hours in severe failure-of-passive-transfer cases. Diagnosis uses blood culture, complete blood count (low or high white cell count with toxic change), and IgG measurement to quantify the passive transfer deficit.
Treatment requires aggressive intravenous antibiotics, plasma transfusion to supplement immunoglobulins, supportive fluids, and intensive nursing care. Even with treatment, mortality in septic foals is significant. Prevention centers on ensuring every foal receives adequate quality colostrum within two hours of birth and on IgG testing at 12 to 24 hours to confirm successful passive transfer before the gut closes to macromolecules. See the neonatal health and vaccination guide for the broader preventive care context.
Further Reading: Neonatal sepsis mechanisms and failure of passive transfer are explained in the Wikipedia overview of neonatal sepsis. The Merck Veterinary Manual covers septicemia in foals including diagnostic criteria and treatment protocols.