SLAUGHTER AND CARCASS TRAITS OF CALVES FROM FIRST-CROSS AND RECIPROCAL BACKCROSS BEEF-COWS

Breed-of-dam and sex-of-calf effects are reported based on observation of 2007 heifer and steer carcasses. The carcasses were derived from L imousin-sired calves born to dams representing 15 F-1 and backcross ge notypes reared at two locations over a period of 5 yr. The calves repr esented Hereford x Angus, Charolais x Shorthorn, Simmental x Shorthorn and all backcross combinations involving Charolais or Simmental with Hereford, Angus or Shorthorn. Carcass traits were analyzed on an unadj usted, a constant hot-carcass weight, and a constant rib-fat depth bas is. The slaughter criteria dictated that steers were heavier at slaugh ter than heifers. They also exhibited higher dressing yield, greater l ongissimus thoracis area, and lower fat depth. Charolais and Simmental breeding was associated with less rib fat depth, greater longissimus thoracis area, a higher proportion of preferred cuts, less dissectible fat, more bone and more lean in the preferred cuts than British beef breeding. Within the European (Charolais and Simmental) and British be ef (Hereford, Angus and Shorthorn) breed groups, breed effects were sm aller, but for carcass composition traits they were frequently signifi cant. When compared with Simmental, Charolais breeding tended to be as sociated with less marbling, less rib fat depth, less dissectible fat and more lean in the preferred cuts. Among the British beef breeds, He reford was associated with the highest proportion of preferred cuts, S horthorn with the lowest rib fat depth - but the highest dissectible f at - and Angus with the most marbling, the greatest longissimus thorac is area and the lowest bone content. This research has demonstrated th at breed effects for carcass composition traits tend to be additive an d that a significant effect may be associated with substitution of as little as one-eighth of the breed composition.