Effects of antibiotics, dried molasses distillers solubles and zeranol in all-sorghum grain rations fed to steers

Abstract

A 23 factorial design was used to examine the effects of the following treatments on the productivity of steers fed in yards on an all-sorghum grain ration : nil vs. 70 mg chlortetracycline head-1 day-1; nil vs. 3 per cent dried molasses distillers solubles; nil vs. 36 mg implant of Zeranol. An additional treatment eompared zinc bacitracin with chlortetracycline. Eighteen groups each of five Hereford steers of a mean initial shrunk liveweight of 273.5 ¦ SE 1.00 kg were used. They were slaughtered at a mean final shrunk liveweight of 399.8 ¦ 2.97 kg. Mean results were: liveweight gain 1 .17 kg day-1, carcase weight gain 0.69 kg day-1, DM feed intake 6.91 kg day-1, feed conversion ratio 6.0. Feeding chlortetracycline resulted in increased carcase weight gain, an improved feed conversion ratio and a reduction in the number of liver abscesses. Regarding productivity, zinc bacitracin was not significantly different from chlortetracycline but it had no effect on reducing liver abscesses. Adding dried molasses distillers solubles caused a decrease in live- and carcase weight gain and an inferior feed conversion ratio. The anabolic implant Zeranol resulted in increased live- and carcase weight gain, increased DM feed intake but no significant differences in feed conversion ratio. The treatments had no effect on eye muscle area or muscle percentage of the carcases. Dried molasses distillers solubles was associated with a lower fat percentage (1 9.5 vs. 20.8 ¦ 0.43; P <0.05). The rationsbsed resulted in an acetic to propionic ratio in ruminal fluid of 0.44 :1. There were no interactions and the usefulness of chlortetracycline and Zeranol and the poorer production using molasses distillers solubles in all-grain diets are discussed.