T H E Effect of Aureomycin on Growth and Reproduction in Swine 1

THE widespread use of antibiotics for feeding swine during recent years has followed early work in that field by Cunha et al. (1949) and Jukes and coworkers (1950). Other reports from a number of workers have indicated that various antibiotics have different optimum levels at which they should be fed. For aureomycin, 5.0 to 10.0 rag. per lb. of feed were found to give satisfactory results during the growingfattening period by Speer and coworkers (1950), Briggs and Beeson (1950 a and b), and Catron et al. (1951). Vestal and coworkers (1952) reported that 10.0 rag. of aureomycin per lb. of feed gave some improvement in reproductive performance, but that 4.5 mg. per lb. proved ineffective. Larson and Carpenter (1952), who used 10.0 rag. of aureomycin per lb. of feed on a group of sows for two successive farrowing periods, reported no apparent effect on reproduction although the sows fed the antibiotic supplement weaned more and heavier pigs. Because of the increasing use of aureomycin in diets for breeding stock, a study was initiated in 1951 in order to secure information on the effect of continuous feeding through successive reproductive cycles and generations. Diets containing relatively high levels of aureomycin (50.0 and 100.0 mg. per lb. of feed) were included in this study along with a commonly accepted level (10.0 mg. per lb. of feed) in an attempt to accelerate or intensify the effect of continuous antibiotic feeding, and to study any possible toxic or undesirable effects of the high levels, as such, on growth and reproduction.