Effects of Salinomycin on Feed Conversion and Ruminal Fluid Characteristics in Fattening Japanese Black Heifers

Abstract

Effects of salinomycin (SL) on daily gain, feed conversion and ruminal fluid characteristics were investigated with 16 Japanese Black heifers.Eight heifers per pen were fed a concentrate supplemented with 0 and 20 ppm SL for 337 days starting at 9 months of age. The amounts and ingredients of concentrates were alterated with the growth stage of animals.The heifers in both groups received daily an equal amount of concentrate with or without SL, but were free access to rice straw and water. Final body weight and average daily gain were significantly (p<0.05) increased by SL feeding and the feed conversion in SL-fed heifers was improved by 11%.Ruminal pH was not consistently affected with supplemental SL.Ammonia nitrogen concentration in ruminal fluid decreased remarkably with supplemental SL.Total protozoa number was decreased by SL feeding but was not so different between control and SL feeding 245 days after the feeding.Total volatile fatty acids (VFA) concentration was not altered notably by supplemental SL.The molar proportion of propionic acid increased, while that of acetic acid and butyric acid decreased, and acetate to propionate ratio decreased with supplemental SL.In the initial period of experiment differences in ammonia nitrogen concentration, protozoa number and VFA molar percentages between control and SL feeding groups were remarkable. The improvement of feed conversion in SL-fedheifers was also more evident in the initial period.