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Performance and carcass traits of crossbred cattle raised in pastures supplemented or not with virginiamycin

Georg Altrak ; Ricardo Fávero ; Gilberto Romeiro de Oliveira Menezes ; Ricardo Kazama ; Marcus Vinicius Garcia Niwa ; Marina de Nadai Bonin ; Max Wender França Martins ; Rodrigo da Costa Gomes
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The aim of this study was to assess performance and carcass traits of crossbred cattle raised grazing tropical grasses, receiving supplement with or without virginiamycin (VM). Steers (n = 49) and heifers (n = 56) produced from matting Nellore, 1/2 Nellore x 1/2 Angus and 1/2 Nellore x 1/2 Caracu dams with Braford, Charbray and Caracu sires were raised grazing tropical grasses (Brachiaria brizantha cv. Marandu) from 9 to 20 mo of age. The animals were divided into eight paddocks of eight hectares each, with care to form groups containing individuals of all genetic groups and balanced in age and average body weight (BW). During the dry season (July to October) cattle received protein supplements containing (n = 52) or not VM (n = 53), formulated for intake of 1 g kg-1 of BW and during the rainy season (November to June) cattle received mineral mixtures containing (n = 52) or not VM (n = 53). The VM was included in the supplements to provide an intake of 45 mg 100 kg-1 of BW. Supplements were provided in open troughs ad libitum and intake was evaluated by weighing monthly leftovers. The BW records were taken every 56 days to calculate average daily gain (ADG) and ultrasound carcass scanning was performed in these occasions to determine ribeye area, backfat thickness and rump fat thickness. The paddocks were considered as experimental units and the variables were analyzed as randomized blocks using GLM procedure of SAS at 5% of significance. The presence of VM did not affect supplements intake in dry and rainy seasons (P > 0.05). The ADG of groups that received protein supplement with or without VM on dry season was similar (0.350vs.0.356 kg day-1; P > 0.05), but cattle that received mineral mixture with VM showed greater ADG than group that received mineral mixture without VM on rainy season (0.661 vs. 0.583 kg day-1; P < 0.05). There were no differences for evaluated carcass traits between the treatments (P > 0.05). The use of VM for animals raised under grazing does not affect supplement intake and ADG on dry season but, offered in the mineral mixture improves performance on rainy season, moreover does not interfere on carcass traits.