PSIV-12 Effects of creep-feeding supplementation on growth performance during the rearing and finishing phases of grazing Nellore young bulls

Abstract The study aimed to evaluate the effect of creep-feeding on growth performance of beef young bulls (n = 40) when they were subjected to an intensive rearing and finishing system. The experiment lasted 325 d, from May/2022 to April/2023, the calves were born in September/2021 and creep-feeding supplementation lasted 170 d, from December/2021 to May/2022. The experimental design used was a randomized block blocked by body weight (BW) of calves in the beginning of supplementation. The experimental units were the paddocks (4 paddocks per treatment, and 5 animals per paddock). The treatments consisted of supplementation on creep-feeding system or not during the nursing phase: control (mineral supplement ad libitum) and creep-feeding treatment (energetic protein supplement, 5 g/kg BWּ animal-1ּ d-1). After weaning, all the bulls were managed similarly with an energetic protein supplement (10 g/ kg BWּ animal-1ּ d-1) during the grazing intensive rearing phase, and 15 gּ/kg BWּ animal-1ּ d-1during the grazing intensive finishing phase) until slaughter. The bulls were allocated to grazing area of Urochloa brizantha cv. Marandu. The data were analyzed using the MIXED procedures of SAS (SAS Institute Inc., Cary, NC, USA, version 9.4). The bulls subjected to creep-feeding system had greater BW at beginning of rearing phase (+14 kg) and beginning of rainy season (+18 kg; P = 0.03; Figure 1). At beginning of finishing phase and slaughter, the bulls had the same BW (P ≥ 0.71; Table 1). The back and rump fat thickness measures showed tendency to be different between the treatments (P ≤ 0.10), where creep-fed animals were greater. Probably, creep-fed bulls slowed down their BW gain during the rainy season on rearing and finishing phases, due to presenting a change in the gain composition. Creep-feeding may have influenced the puberty of these bulls, and caused them to begin deposition of fat earlier than those that did not receive creep-feeding. Thus, the animal tends to balance BW with changes in the gain composition, and the percentage of muscle tissue tends to reduce, while the proportion of fat tends to increase. Creep-feeding supplementation increased the animals weaning weight by 14 kg but, it was not able to influence the slaughter weight due to changes in the gain composition.