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The effect of oestrogenic agents on live-weight gain, carcass composition, reproductive function and tissue residues in intensively reared beef bulls given cereal-based diets

Published online by Cambridge University Press:  02 September 2010

A. R. Peters ,
J. R. Southgate ,
E. Aughey  and
S. N. Dixon
A. R. Peters
Affiliation:
British Technology Group, 101 Newington Causeway, London SE1 6BU
J. R. Southgate
Affiliation:
Meat and Livestock Commission, PO Box 44, Queensway House, Bletchley, Milton Keynes MK2 2EF
E. Aughey
Affiliation:
University of Glasgow, Department of Veterinary Anatomy, Bearsden Road, Bearsden, Glasgow G61 10QH
S. N. Dixon
Affiliation:
Food and Veterinary Laboratory Ltd, 25-26 Frederick Sanger Road, Surrey University Park, Guildford GU2 5YD
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Abstract

The use of oestradiol-17β was evaluated in cereal-based beef production on 14 farms with 450 bulls. Half of the bulls were implanted subcutaneously in the ear with a silastic rubber implant containing 45 mg oestradiol-17β Representative bulls close to mean weight for each group were selected for slaughter on the same day at the end of the trial for carcass measurements. The remaining bulls were slaughtered at the farmers' discretion. Where possible, slaughter live weight (208 bulls), carcass weight (412) and European Economic Community carcass classification (353) were recorded. Implanted bulls had higher gains only in the first 3 months (+76 (s.e. 17) g/day; P < 0·001) and had heavier carcasses with the extra weight in the forequarter (+2·3 (s.e. 0·61) kg; P < 0·001), better carcass shape (+0·9 (s.e. 0·3) points; P < 0·01) and more subcutaneous fat in the thin flank (+1·3 (s.e. 0·6) g/kg; P < 0·05). Implanted bulls selected for slaughter by farmers were not slaughtered earlier, but killed out better (+0·7 (s.e. 0·3) g/kg; P < 0·05) and had heavier carcasses (+4·6 (s.e. 0·5) kg; P < 0·01) of better shape (+0·8 (s.e. 0·3) points; P < 0·05).

The use of zeranol was evaluated in cereal beef production on 15 farms with 385 bulls. Half received 36 mg zeranol which was repeated after 6 months. Forty-four bulls were selected for detailed carcass assessment as above. Implanted bulls had daily gains 0·06 (s.e. 0·01) kg greater (P < 0·001) than controls. Farmers chose to slaughter implanted bulls 8·3 (s.e. 3·8) days earlier (P < 0·05) at only marginally heavier weights (+4·8 (s.e. 3·1) kg; P = 0·08). More implanted bull carcasses were distributed in better shape and higher fat classes (P < 0·01). There were no significant differences in fore- and hindquarter and thin-flank tissue proportions. Oestradiol treatment marginally decreased testis weight in slaughtered bulls whereas zeranol treatment had no significant effect although epididymal weight was decreased in zeranol treated bulls. There were no clear effects of either treatment on testicular structure, but both oestradiol and zeranol caused a degree of disruption to the epididymal epithelium. Zeranol concentrations in treated animal tissues were not significantly different from those in control animals.

Type
Research Article
Information
Animal Production , Volume 47 , Issue 2 , October 1988 , pp. 215 - 221
Copyright
Copyright © British Society of Animal Science 1988

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