Influência do tamanho de grupo sobre o comportamento e desempenho produtivo de touros nelore confinados no período chuvoso

Abstract

In order to increase productivity, there is a global trend toward reducing the space allowance per animal in feedlot systems, which can negatively affect welfare, especially during the rainy season, due to the accumulation of manure and mud in the pens. Given this, the objective of the present study was to evaluate whether reducing group size and increasing space availability improves animal welfare and, consequently, the performance of feedlot cattle during the rainy season. A total of 1,125 Nellore bulls, aged 24 ± 4 months and with an initial body weight (BW) of 395 ± 18.7 kg, were used in a completely randomized design with the following treatments: i) pen with 50 animals (B50), ii) pen with 75 animals (B75), and iii) pen with 100 animals (B100). Thus, in treatments B50, B75, and B100, each animal had 30 m² of usable area, 100 cm of feed bunk, and 4.8 cm of linear waterer space; 20 s m² of usable area, 67 cm of feed bunk, and 3.2 cm of linear waterer space; and 15 m² of usable area, 50 cm of feed bunk, and 2.4 cm of linear waterer space, respectively. All animals received the same diet during the 81 day experimental period. Animal welfare indicators based on the environment (mud depth) and on the animals themselves were used, such as behavioral indicators (number of animals standing, lying down, at the feed bunk, or at the waterer; and incidence of fighting, head-butting, and mounting attempts), comfort (dirtiness score of the animals), and health (coughing and sneezing frequency, percentages of animals with diarrhea, lameness, and nasal and ocular discharge). Performance indicators (dry matter intake (DMI), final weight, average daily gain (ADG), and feed efficiency) and carcass characteristics (hot carcass weight, dressing percentage, total carcass production, trimming percentage, and carcass losses) were also evaluated. In general, the results showed that B50 provided better environmental and social conditions, as evidenced by lower mud depth (P < 0.05), lower percentages of dirty animals (P < 0.0001), and a lower incidence of agonistic behavior among individuals (P < 0.05). Group size did not affect the percentage of animals lying down, standing, or feeding (P > 0.05), nor did it influence overall growth performance (P > 0.05). Differences were observed only for dry matter intake (DMI) (P < 0.001) and total carcass production (TCP) (P < 0.001), where the B50 treatment resulted in the highest DMI, and B100 resulted in the highest TCP compared to the other treatments. In conclusion, for regions with low rainfall during the confinement period (around 472 mm) and a total area per bay of 1,500 m² , it is recommended to adopt 100 animals per group, as the reduction did not affect the animals’ performance.