The effect of antibiotics on ammonia accumulation and protein digestion in the rumen

Abstract

A study was made of the feasibility of using antibiotics to reduce ruminal deamination of protein that comprised 27% of the organic matter in a diet of lucerne hay and casein. Six sheep were each dosed with a different antibiotic. At the levels given, penicillin and erythromycin reduced rumen ammonia levels by about 35%, but also reduced food intake. Chloramphenicol reduced rumen ammonia by about 50% but neomycin, oxytetracyclene, and streptomycin had little effect.

When all six sheep were subsequently dosed with chloramphenicol at 1 g/day the levels of rumen ammonia were reduced only to 85% of the control. The antibiotic had little effect on the extent of digestion of protein, organic matter, and cellulose, both in the stomach and in the whole alimentary tract, and on parameters associated with the movement of digesta through the stomach

The quantity of nitrogen passing from the stomach in forms other than ammonia was 52–54% of intake during both the control and treatment periods. Much of this nitrogen probably passed from the stomach in the form of microbial protein, which indicated that the dietary protein was extensively digested. In consequence of the loss of nitrogen from the stomach, the protein apparently digested in the intestines was equivalent to only about 14.5 g/100 g digestible organic matter.