In Vitro Effects of the Thiopeptide A10255 on Ruminal Fermentation and Microbial Populations

¹ Delaware Agricultural Experiment Station, Department of Animal Science and Agricultural Biochemistry, College of Agricultural Sciences, University of Delaware, Newark 19717-1303
² USDA-ARS, Beltsville Agricultural Research Center, Ruminant Nutrition Laboratory, Beltsville, MD 20705

Experiments used unadapted mixed cultures of ruminal microorganisms in batch or continuous culture fermentation to investigate the effect of a thiopeptide, A10255, on ruminal fermentation and microbial populations. After 24 h of fermentation in batch culture, addition of A10255 (.5 to 20 ppm of the culture fluid) to 0, 45, 60, and 75% concentrate diets had no effect on total VFA but increased molar proportion of propionate and decreased butyrate. The molar proportion of acetate was decreased by treatment only in the 0 and 75% concentrate diets. The increase in molar proportion of propionate by 20 ppm of A10255 was less than the increase caused by a similar concentration of monensin. The same concentration of A10255 (20 ppm) decreased ADF digestion less than 20 ppm of monensin. In continuous culture, A10255 (33 mg/kg of dietary DM) did not affect total VFA concentration, culture pH, OM digestion, or ADF digestion. Ruminal bacterial populations of total anaerobes and lactate-producing, lactate-utilizing, cellulolytic and amylolytic bacteria were unaffected by treatment. However, molar proportions of acetate, butyrate, and isovalerate were decreased, and propionate was increased, by addition of A10255.

Key Words: thiopeptide • ruminal fermentation

Submitted on February 14, 1992
Accepted on April 27, 1992