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The Effects of Two Shipping Treatments on the Carcass Characteristics of Bulls Implanted with Zeranol and Unimplanted Steers^1,2,

Agriculture Canada³, Lacombe, Alberta, Canada TOC 1SO

Abstract

A total of 144 male crossbred calves were allocated to four management treatments (bulls; steers; bulls implanted with zeranol at 100 d of age and re-implanted at 69, 93 and 56 d thereafter; bulls implanted with zeranol at 168 d of age and re-implanted at 93 and 56 d thereafter), and two pre-slaughter shipping treatments (minimum pre-slaughter stress with cattle shipped and slaughtered within 4 h of leaving the feedlot pen; moderate pre-slaughter stress with cattle mixed, trucked 160 km and slaughtered up to 24 h of leaving the feedlot pen) in a 4 x 2 factorial arrangement. Management treatment had no significant effect on carcass pH (45 min), carcass muscle temperature (45 min), or peak shear-force of cooked longissimus muscle. Steers had significantly lower dressing percentage, warm-carcass weight, hide weight and carcass-lean content, but higher marbling score, fat thickness and intramuscular-fat content than all treatments with bulls. Minimum pre-slaughter stress resulted in significantly lower dressing percentage, warm-carcass weight, and carcass pH (45 min), but generally had no effect on carcass tissue-yield measurements compared with the moderate stress treatment. Implanted bulls produced carcasses with significantly darker meat, higher 24-h pH and lower meat expressible juice than bulls and castrates for the moderate pre-slaughter stress treatment. These results provide evidence that zeranol implantation in bulls had a minor influence on carcass characteristics, and did not reduce the incidence of dark-cutting carcasses in young bulls subjected to moderate pre-slaughter shipping stress.

¹ Scientific Paper No. 520, Lacombe Res. Sta., Res. Branch, Agriculture Canada. This publication is in commemoration of the Centennial of the Experimental Farm Stations Act in Agriculture Canada, 1886–1986.

² The authors thank the staff of the Lacombe Meat Res. Center for performing the carcass dissections and acknowledge partial funding of this project from the Farming for the Future Program administered by the Government of Alberta.

³ Meat Res. Center.