The effect of social buffering on fear responses in sheep (Ovis aries)

Abstract

Fear in farm animals has been extensively studied because of its close relation to animal welfare. Numerous studies have categorized the behavioral responses of animals to stimuli that can elicit a fear reaction under social isolation conditions. However, farm animals are highly social and therefore these responses could be conditioned by isolation. The objective of this study is to evaluate the potential buffering effect of the social environment on the fear responses of sheep, comparing the reactivity of individuals within different social environments. We studied the reactivity of 15 ewes (focal individuals) in isolation, and within groups composed of 5 and 10 individuals, randomly alternating the presence of a sudden stimulus with a normal, non-stimulus situation (control). The XY coordinates and the behavior of each focal individual (inactivity, exploration, fast movements, attempt to escape, filial interactions, agonistic interactions, and other activities) were recorded, at 1min intervals during tests lasting 15min, using the Chickitizer software. Euclidean distances were subsequently obtained, and total traveled distance, net distance, minimum distance, maximum distance, and path sinuosity (ND/TD) calculated. Results show a significant effect of both the presence/absence of stimulus and the group size on the distance measures, exploration and filial interactions (P≤0.01). Moreover, the buffering effect of group size was demonstrated by the lower incidence of fast movements (P<0.001) and escape attempts (P<0.001). The interaction between the presence/absence of stimulus and the group size was significant for inactivity (P=0.001). Results show a marked effect of the stimulus presence, regardless of group size. However, stress reactions due to social isolation were substantially greater than those elicited by the mere presence of the stimulus. These results highlight the importance of the management procedures, particularly when animals need to be isolated from the group.