No abstract

Fourteen trials were conducted to evaluate the effects of feeding monensin at 33 ppm alone, tylosin at 11 ppm alone and the two feed additives in combination on the average daily gain, average daily feed intake, feed:gain ratio and the incidence of liver abscesses in feedlot cattle. Monensin reduced feed intake and improved feed efficiency (P less than .05), and had no effect on average daily gain. Tylosin improved average daily gain (P less than .05) and had no effect on daily feed intake. The effect of tylosin on feed efficiency approached significance. The interaction of monensin and tylosin was nonsignificant for daily gain, daily feed intake and feed:gain ratio. Monensin had no effect on liver abscess incidence, while tylosin reduced abscess incidence from 27 to 9%.

Four feedlot experiments with 774 cattle have been completed during 1969 to 1970 evaluating two forms of tylosin activity (50, 75 and 100 mg per head per day continuously of tylosin phosphate or tylosin urea adduct) in high concentrate rations. Continuous administration of these three levels of antibiotic activity from either form of tylosin (1) reduced the incidence of liver abscesses, (2) increased average daily gain, and (3) improved feed conversion of feedlot cattle. Mathematically combining data from all levels of both forms of tylosin demonstrated an 81.8% reduction (24.1% control vs. 4.2% treated)in incidence of liver abscesses (P < .01), a 5.9% increase (2.23 lb. [1.01 kg] control vs. 2.36 lb. [1.07 kg] treated) in average daily gain (P < .05) and a 3.1% improvement (7.65 control vs. 7.41 treated) in feed conversion (P < .10). Control cattle with normal livers gained 17.0 lb. (7.7 kg) more weight during the feeding period than control cattle with abscessed livers.