EFFECTS OF PLANE OF NUTRITION AND SLAUGHTER WEIGHT ON THE CARCASS COMPOSITION OF SERIALLY SLAUGHTERED BULLS, STEERS AND HEIFERS OF 3 BREED CROSSES

Effects of plane of nutrition and slaughter weight on the carcass comp osition (estimated from the dissection of fore-rib joints) of 236 Frie sian (F), Limousin X F and Belgian Blue X F bulls, steers and heifers were examined. They were reared under uniform management using high-fo rage diets until 12 to 13 months of age (372 kg live weight) and were then given a diet consisting of grass silage and concentrates (2:1 on DM basis) either ad libitum or at 80% of ad libitum intake. Representa tive groups were slaughtered initially and serially, bulls at 560, 610 and 660 kg, steers at 510, 560 and 610 kg and heifers at 460, 510 and 560 kg. Reducing food intake reduced estimated carcass fat content by 22 (SEM 2.1) g/kg and increased lean and bone contents by 14 (SEM 1.7 ) and 4 (SEM 0.7) g/kg. Increasing slaughter weight increased carcass fat content and reduced lean and bone contents, the effects being sign ificantly greater in steers and heifers than in bulls, It is concluded that for animals reared on high-forage diets and slaughtered at moder ate levels of fatness, reducing dry matter intake during the finishing stage by 20%, reduced estimated carcass fat content and increased lea n and bone contents, although the effects were not as great as those r ecorded in previous studies in which the animals were given high-conce ntrate diets, the treatments were imposed from early life or the anima ls were fatter at slaughter. Carcass fat content of bulls was much les s sensitive to slaughter weight than that of steers or heifers. There were no significant interactions between plane of nutrition and either slaughter weight or breed.