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The effects of ration type and ralgro implantation on the growth rate, feed efficiency and carcass composition of Hereford steers Nwokolo, Emmanuel R. N.

Abstract

Five ration types as well as Ralgro implantation were evaluated in a 5 x 2 factorial experiment to determine their effect on growth rate, feed efficiency and carcass composition of Hereford steers. The five ration types were 100% barley, 50% barley-50% alfalfa cubes, 100% alfalfa cubes, barley followed by cubes, and cubes followed by barley. Implantation of 36 mg Ralgro was done after 12 weeks on the experimental diet. The animals were weighed every two weeks, the morning feed being withheld until weighing had been completed. Rib eye muscle area as well as fat depth over the eye muscle were used to estimate carcass lean and carcass fat. Rib eye area and fat thickness were measured monthly using a USM 2F Krautkramer Ultrasonic flaw detector. The feeding trials lasted 28 to 36 weeks at the end of which the steers were probed for rib eye area and fat depth. They were then starved for 12 hours, weighed and shipped to a packing house. Rib eye muscle area and fat thickness were determined on the chilled carcasses. Dressing percentage as well as cutability were also determined on each carcass. The carcasses were then graded. Average daily gain, group feed efficiency and feed cost/kg gain were computed for each ration type. Results indicated that only the 100%, alfalfa ration supported significantly lower average daily gain (P≤0.05) than other rations. There were no differences between the ration types in terms of the average carcass fat and carcass lean. The 100% barley ration, the 50%, barley ration as well as the ration in which alfalfa was followed by barley, all gave rise to significantly higher dressing percentages (P≤0.05). Over the entire growth period, implantation of 36 mg Ralgro did not significantly improve either the growth rate or the carcass composition of the steers so treated. A breakdown of the growth period indicated that within 60 days post implantation, administration of 36 mg Ralgro caused a significantly higher growth rate than controls. Its effect, however, disappeared after 60 days. There were significant but low positive correlations between the area of rib eye estimated by the ultrasonic method just prior to slaughter and that determined on the carcass by acetate paper tracings (r = 0.27) or by the plastic grid method (r = 0.30). There was, however, a very high correlation (r = 0.72) between the acetate paper tracings and the plastic grid method of determining the area of rib eye muscle. Computation of the feed cost/kg gain indicated that at prevailing prices the all-barley ration was the cheapest to raise steers on while the all-alfalfa ration was by far the most expensive.

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