376 Effects of slaughter age on growth and carcass traits of grazing Nellore young bulls.

Abstract The study evaluated the growth performance during growing and finishing phases and carcass traits of Nellore bulls slaughtered at 20 vs. 30 mo of age. At weaning (day 0), 80 Nellore bulls (age = 8 mo of age) were blocked by body weight (BW = 245 ± 10.7 kg) and were randomly allocated into 1 of 16 brachiaria pastures (5 bulls and 1.0 ha/pasture). Treatments were randomly assigned to pastures (8 pastures/treatment) and consisted of high supplementation (1.0% of BW daily during growing, day 0 to 235, and then 1.5% of BW daily during finishing, day 236 to 334; HIGH) or low supplementation (0.1% of BW daily during growing, day 0 to 535, and then 0.3% of BW daily during finishing, day 536 to 667; LOW). Bulls assigned to HIGH and LOW supplementation were slaughtered at 20 and 30 mo of age, respectively. Data was analyzed using the MIXED procedures of SAS (SAS Institute Inc., Cary, NC, USA, version 9.4). Body weight at slaughter did not differ (P = 0.65) between treatmens, but carcass traits were affected (P < 0.01). Average daily gain was greater (P < 0.01) for HIGH vs. LOW bulls. Hot carcass weight and dressing were greater (P < 0.01) for HIGH vs. LOW bulls (316 kg vs. 293 kg and 56.1% vs. 52.4%, respectively). Renal-pelvic-inguinal fat was greater (P < 0.01) for HIGH vs. LOW (0.94% vs. 0.39% of BW). Cold carcass weight was greater (P < 0.01) for HIGH vs. LOW bulls (314 kg vs. 293 kg). Carcass average daily gain was greater (P < 0.01) for HIGH vs. LOW bulls. Longissimus muscle area and rump fat thickness at slaughter were greater (P < 0.01) for HIGH vs. LOW (97.7 cm² vs. 74.5 cm² and 7.29 mm vs. 4.48 mm). Meat lipid and backfat thickness were greater (P < 0.01) for HIGH bulls. Meat shear force was lower (P = 0.03) for HIGH vs. LOW bulls (31.2 N vs. 35.2 N). Therefore, high supplementation during growing and finishing phases shortened the cycle, producing younger animals at slaughter with greater carcass traits. Despite the similar BW at slaughter, low supplementation did not enchance carcass traits compared to high supplementation.