Stress-induced Behaviour in Rams of Three Different Sheep (Ovis aries) Breeds: Indicator of Welfare?

Abstract

Growing importance of and concern for the welfare of farm animals within production systems has been the basis for an enormous amount of scientific studies. The goal of the present study was to investigate whether both vocal and social behaviour of sheep, under specific stress-inducing situations, could be used as an indicator of the animals’ welfare status. Two separate experiments were carried out with 2-3 year old adult rams. The animals were of three breeds, namely Barbados Blackbelly Cross, Local Garut and Composite Garut. In the first experiment twelve clinically healthy animals, four from each breed, were subjected to three different levels of social isolation. The animals were held completely alone, in the presence of a human and alone in a group pen adjacent to a pen with conspecifics. During the isolation sessions both vocal and locomotive behaviour of each animal were recorded. The recorded calls were acoustically analyzed using specialized acoustic software. The results showed that the levels of isolation were characterized by very specific behavioural responses with an increased amount of locomotor activity and vocalization in partially isolated animals. The animals that were completely isolated showed a higher amount of inactive behaviour. No specific differences were found in the behaviour of animals that were held completely alone and the ones which were in the presence of a human observer. Acoustic analysis of the recorded calls showed significant differences in a number of temporal and structural features. Spectral analysis revealed the most notable differences in the amount of sound energy integrated in the calls. Differences were found in both locomotive and vocal behaviour based on isolation level and breed. The second experiment focused on the effect of stocking density on the social behaviour of newly regrouped rams. Thirty-six animals were subjected to three different stocking density levels, namely low (3.2 m2/ram), medium (1.6 m2/ram) and high (0.8 m2/ram). Recorded data consisted of frequencies of agonistic-, exploratory, locomotive-, aberrant-, inactive-, self-care-, mating- and vocal behaviour. The results of this experiment showed that the animals responded differently to the different stocking density levels. The highest stocking density level was characterized by the highest number of inactive behaviour and the lowest number of locomotor activity. There were also significant differences found in the frequency of displayed behaviours based on the amount of time the animals had spent within the new group settings. The amount of agonistic-, mating- and exploratory behaviour was found to be significantly higher on the day of regrouping as compared to the level of these behaviours on the day after regrouping. Significant differences were also found in the behavioural response of animals from different breeds. The results from both experiments thus lead us to conclude that both vocal- and social behaviour of rams are able to provide humans with important information on their affective state which may be helpful in the design of production systems that are beneficial to the animals their welfare.