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

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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 per day; nil vs. 3% dried molasses distillers solubles; nil vs. 36 mg implant of Zeranol. An additional treatment compared zinc bacitracin with chlortetracycline. Groups (18) each consisting of 5 Hereford steers of a mean initial shrunk liveweight of 273.5 .+-. SE [standard error] 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, carcass weight gain 0.69 kg day-1, DM [dry matter] feed intake 6.91 kg day-1, feed conversion ratio 6.0. Feeding chlortetracycline resulted in increased carcass 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 carcass weight gain and an inferior feed conversion ratio. The anabolic implant Zeranol resulted in increased live- and carcass 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 carcasses. Dried molasses distillers solubles was associated with a lower fat percentage (19.5 vs. 20.8 .+-. 0.43; P < 0.05). The rations used 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.

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