When the bowel’s natural system of checks and balances is altered, the resulting endotoxin release can cause serious health issues

Although we’d like to think our horses are “sterile” on the inside, they are, in fact, harboring vats of micro-organisms within their intestinal tracts. In the normal, healthy bowel resident microbes limit the overgrowth of pathogenic bacteria. One type of microbial inhabitant, Gram-negative bacteria, which helps break down fibrous feed, releases a portion of its cell wall when it multiplies and then dies. What’s released is called endotoxin.

Normally, bacteria or their components are restricted from traveling beyond the bowel’s interior by a complex intestinal barrier; the bowel lining’s mucosa (mucus-secreting membrane lining all body passages that communicate with the air) is made of epithelial cells that shield against endotoxin. Also, enzyme and antibody secretions block endotoxin passage. And when small amounts of endotoxin do make it through the mucosal barrier into the liver’s circulation, specialized immune cells envelop and eliminate the toxin.

However, when the bowel’s natural system of checks and balances is altered and microbial overgrowth leads to a die-off of Gram-negative bacteria, the resulting endotoxin release can cause serious health issues. “Problems develop when the intestinal barrier is injured, such as occurs with gastrointestinal disease or surgery, from reduced intestinal blood flow related to intestinal displacements,” explains Anthony Blikslager, DVM, PhD, Dipl. ACVS, professor of equine surgery at North Carolina State University’s College of Veterinary Medicine. “In addition, nonintestinal events such as septicemia (bacteria in the bloodstream) or post-foaling retained fetal membranes can cause large amounts of endotoxin to be absorbed into the central circulation.” Bacterial, vi