Abstract
A total of 87 crossbred gilts were used in two trials to determine the influence of feeding a high level (200 gm. per ton of feed) of zinc-bacitracin or tylosin at breeding time on the apparent ovulation rate, embryo survival to 25 or 40 days and embryo development. In both trials the antibiotics increased gains of the gilts significantly and feed conversion was markedly improved. Apparent ovulation rate was slightly higher for the antibiotic-supplemented gilts, but the differences were not significant. Overall embryo survival favored the control gilts by a small margin, but again this was not significant. Embryo development, as measured in terms of weight and length of embryos, revealed small, non-significant differences in favor of the antibiotic-supplemented gilts. Thus, it appears that in swine herds where litter size is good, high level antibiotic therapy at breeding time would prove ineffective as a means of increasing litter size. Copyright © 1963. American Society of Animal Science . Copyright 1963 by American Society of Animal Science