Antibiotics in Rumen Digestion and Synthesis. I. The Effect of Aureomycin on Rumen Digestion and the Passage of Nutrients from the Rumen during Specific Intervals after Feeding

Depart~ne~tts of Dairy and Agrieultt~ral Chemistry, Michigatt Agricult~tral Experiment Statio~ East La~tsingMany investigators have shown that various antibiotics are beneficial in promoting growth, in reducing digestive disturbances, and in increasing feed efficiency in swine and poultry, but there are discordant reports in the literature concerning the efficiency of antibiotics in ruminant nutrition.An increase in growth was obtained in most cases when aureomycin was included in the ration of young dairy calves (3, 8, 9, 11, 12, 13, 17), but several investigators (4, 6, 14) reported that aureomycin produced adverse effects when fed to steers and lambs.L,oosli and Wallace (11) and Jacobson et al. (8) observed that feed consumption was greater when aureomycin was fed to calves, but less total digestible nutrients were required to make one pound of gain.Bell et aI.(4) fed 0.6 g. of aureomycin daily to yearlit~g steers and observed a marked anorexia and diarrhea within 48 to 72 hours after feeding.A digestion trial showed that the ingestion of 0.2 g. of aureomycin daily apparently decreased the digestibility of dry matter by 15 per cent and crude fiber by 50 per cent.Nemnann et al. (14) found that 2 rag. of aureomycin per pound of air-dried feed caused a severe reduction in the appetite of yearling beef heifers for a few days, but partial recovery was made and the daily gains were not significantly different from those obtained on the basal ration.Colby et al. (6) ,observed that fattening lambs fed 100 mg. of aureomycin daily went almost entirely off-feed and lost weight.Jordan and Bell (10) noted that fattening lambs receiving 6 to 12 mg. of aureomycin daily made faster and more efficient gains than the controls.In view of the conflicting reports in the literature concerning the effect of aureomycin in ruminant nutrition, feeding experiments were conducted to ascertain the influence of aureomycin on rumen digestion and the synthesis ,of certain nutrients in the rumen of 2-year old steers and to observe also the effect of this antibiotic on the bacterial population in the tureen and feces.The present paper is the first of a series and is primarily concerned with the effect of aureomycin on rumen digestion and the rate of passage of certain nutrients from the rumen.