Physiological and microbiological changes in the abomasum of sheep infected with large doses of Haemonchus contortus

The pH, PO2 and the number of viable bacteria per ml of abomasal fluid were recorded before and after administering large doses of infective larvae of H. contortus to sheep. Highly significant increases were observed in the pH, in numbers of viable bacteria and in the proportion of oxygen-sensitive bacteria in the abomasal fluid during the first 10 to 14 days of infection. At the same time a decrease in the abomasal fluid PO2 was recorded. Subsequently a slow recovery of pH, PO2 and bacterial numbers to pre-infection values ensued. The microbiological and physiological changes occurring in the abomasum of sheep after infection with H. contortus are discussed with reference to these results.