Effect of Defaunation on Ruminal Volatile Fatty Acids and pH of Steers Fed a Diet High in Dried Whole Whey

Three rumen fistulated steers (approximately 482 kg) were fed a diet containing 45% dried whole whey at 6.4 kg dry matter per day. After steers were adjusted to the diet, rumen ciliate protozoal numbers, pH, and volatile fatty acid concentration were measured. Steers then were defaunated by sodium diocytyl sulfosuccinate (360 g over 3 days), and measurements were repeated. In the presence of a high ciliate population (10 s to 106 cells/ml), rumen fermentation was characterized as a high butyrate fermentation (~27 molar %), whereas in the absence of ciliate protozoa a high propionate fermentation existed (28 to 35 molar %). Ruminal pH was higher in the faunated state, whereas volatile fatty acid concentration tended to be higher in the defaunated state.