The behaviour of young Friesian bulls during social re-grouping at an abattoir. Influence of an overhead electrified wire grid

The response of young Friesian bulls to social re-grouping, and the use of an overhead electrified grid to control their behaviour, was investigated in two trials at an abattoir. Behaviour was observed continuously for 3 h after social re-grouping. Blood and muscle samples were collected at slaughter and the incidence of carcass bruising and dark-cutting beef was determined on the following day. Mounting was the most common behaviour during social re-grouping, followed by mock fighting and chin resting. The proportion of mounting and chin resting interactions which occurred between “unfamiliar” bulls was much higher than that between “familiar” bulls. The overhead electric grid effectively reduced mounting activity and also chin resting. There was evidence that much of the inhibited mounting activity between “unfamiliar” bulls was redirected and expressed as an increase in mock fighting activity between “unfamiliar” bulls. No adverse behavioural responses to the electric grid were observed. The electric grid influenced the physiological response to social re-grouping, particularly in Trial I in which the animals were more active. In the pen with the electric grid, the muscle glycogen concentration at slaughter was much higher and the final pH value of the meat much lower, as was the proportion of dark-cutting carcasses and the amount of bruising on the carcasses. Animals that were re-grouped in the absence of the electric grid had higher circulating levels of cortisol, non-esterified fatty acids and creatine kinase activity, suggesting a more vigorous physical response to re-grouping. Mounting was the most important activity in depleting glycogen in M. longissimus dorsi, and it accounted for 72 and 54% of the variance in glycogen in Trials I and II, respectively. Similarly, mounting was the most important behaviour in raising the final pH value of the meat and accounted for 80 and 54% of the variance in pH in Trials I and II, respectively. In Trial I, the number of times an animal was butted accounted for 44% of the variance associated with carcass bruising, while an additional 21% was accounted for by the number of times an animal mounted. It was concluded that mounting activity between “unfamiliar” bulls was the principal behaviour responsible for dark-cutting beef under these conditions. An electrified overhead grid was effective in reducing the frequency of mounting and preventing dark-cutting.