Quantitation of Endotoxin in Cell-Free Rumen Fluid of Cattle

Free endotoxin in rumen fluid of cattle was demonstrated by death of mice injected intra-peritoneally with cell-free rumen fluid fraction potentiated with 20 µg actinomycin D (Am D). The toxic principle was resistant to heat, was inactivated by acid and alkali, was protected by cortisone and was not lethal to endotoxin-tolerant mice. Adapting the procedure to quantitate free endotoxin concentration in rumen fluid in cattle, we found the concentration of free endotoxin to be considerably higher in grain-fed than in hay-fed cattle. Concentration was not related to the number of gram-negative bacteria in the rumen; hence we postulate that certain factors, as yet unknown, may favor release of free endotoxin from intact gram-negative bacteria.