PS11-11. Effects of Group Size on Intake, Behavior, and Performance of Bulls Finished in a Commercial Feedlot During the Rainy Season.

Abstract In recent years, finishing cattle in feedlots during the rainy season has increased, highlighting the need for strategies to mitigate muddy conditions while maintaining animal performance and welfare. Thus, this study aimed to evaluate the effects of three group sizes (50, 75, and 100 animals per pen) on performance, social interactions, and animal welfare indicators in feedlot cattle. The trial was carried out in a commercial feedlot. A total of 1,125 Nellore bulls (IBW = 380 ± 20 kg; 5 replicates per treatment) were randomly assigned to one of the following treatments: pen with 50 animals (P50), pen with 75 animals (P75), and pen with 100 animals (P100). Each pen had an area of 1,500 m² (50 m × 30 m) and 2.4 m of water trough space. Thus, animals in treatments P50, P75, and P100 had 30, 20, and 15 m² of pen area per animal; 1.0, 0.67, and 0.50 m of bunk space per animal; and 4.8, 3.2, and 2.4 cm of water trough space per animal, respectively. Pens had an unpaved surface with a 4% slope. During the entire confinement period (110 d), a total precipitation of 472 mm was recorded. The same finishing diet was provided to all treatments. Animal-based and environmental indicators were assessed weekly. Maintenance behaviors were recorded daily for 6 h (0600–1000 and 1500–1700 h) using a video camera (VIP 5232 Speed Dome, 2 MP, 32×; Intelbras, Brazil). The DMI fluctuation was calculated as the difference in intake between consecutive days. Performance and carcass traits were also assessed. Data were analyzed as a randomized complete block design using the SAS MIXED procedure (α = 0.05), with pen as the experimental unit. The P50 treatment had lower mud depth (P = 0.01) than P75 and P100, which did not differ from each other. Group size affected body cleanliness (P < 0.01), with a higher proportion of dirty animals as group size increased (51, 77, and 84% for P50, P75, and P100, respectively). Group size also affected the number of animals fighting (P = 0.01). The number of these activities was lowest in P50, intermediate in P75, and highest in P100. Dry matter intake was greatest in P50 (9.3 kg/d), intermediate in P75 (9.0 kg/d), and lowest in P100 (8.7 kg/d; P < 0.01). No differences were obtained for final BW, ADG, hot carcass, and dressing. However, total carcass yield increased with group size (P < 0.01), reaching 14,571, 21,608, and 28,639 tonnes for P50, P75, and P100, respectively. Overall, group size affected intake and animal behavior but did not affect performance. Thus, up to 100 bulls can be housed in a 1,500 m² pen during the rainy season.