Avaliação do comportamento social dos bovinos confinados em diferentes tamanhos de lotes

Abstract

The aim of this study was to evaluate the social behavior of feedlot cattle finished in three different group sizes. The animals (1440 Nelore with 20 months of age weighing 294 kg) were subdivided into three treatments according to group size, namely TL80 (group with 80 animals), TL160 (group with 160 animals) and TL240 (group with 240 animals). Social behavior was assessed by counting the frequency of occurrence of negatives social behaviors as head displacement (HD), mount (MO), fights (FI) and a positive social behavior as head play (HP). Evaluations took place up to 10 meters from the trough between 7:00 and 11:00 and between 15:00 and 17:00h, with two-day intervals in the first two weeks and then biweekly. For the analysis of social behavior variables, the frequency of occurrence of the respective categories was used every 30 minutes and the data were divided according to the period, as follows: adaptation period (first 15 days), post adaptation period (after 15 days until the end of the experimental period) and period of day (morning and afternoon). To evaluate the effects of treatment on behaviors, the PROC MIXED command was used in a repeated measurement analysis over the days. Comparisons between means were adjusted by the Tukey test and the results were considered significant when P < 0.05. During the adaptation period, a significant effect of the confinement day was observed only on the TM frequency. In the period after adaptation, TL240 animals remained with a higher frequency of TM occurrence (3.02; SEM = 0,34) when compared to TL80 (1.14; SEM = 0,34) and TL160 (1.13; SEM = 0,34) wich did not differ from each other and lower mean HP (1.87; SEM = 0,46) when compared to animals from TL80 (3.35; SEM = 0,46) and TL160 (2.37; SEM = 0,46), which also did not differ from each other. The day period had an effect on the TM variable (4.80 and 3.39; SEM = 0,43, for the afternoon and morning, respectively). Cattle confined in groups of 80 and 160 animals have a lower frequency of negative social behaviors and stabilize them more rapidly over the time.