Reactions of sheep towards three sets of emotional stimuli: (In)Consistency in respect to stimulus valence and sheep identity

Abstract

There is an increasing interest in affective states in applied animal behaviour science, because these states are thought to reflect welfare from the perspective of the animals. Also, it can be expected that individuals differ in how they consistently react to emotional challenges. Recently, we conducted three experiments in which the same sheep were repeatedly confronted with either physical, social or thermal stimuli that presumably varied in their valence. These sheep had been housed in either unpredictable, stimulus-poor or predictable, stimulus-rich housing conditions in order to manipulate their long-term mood. When the sheep were exposed to the stimuli, we measured general activity, ear movements, ear postures and frontal cortical haemodynamic changes as indicator variables for their emotional reaction. In the meta-analysis presented here, we searched for effects of the presumed valence and mood state on the indicator variables. Furthermore, we investigated the unexplained between- versus within-subject variability as an indicator of personality. Deoxy- [HHb] and oxy-haemoglobin concentrations [O2Hb] as well as general activity showed weak linear relationships with presumed valence. Sheep from the unpredictable, stimulus-poor housing conditions were generally more active and showed more ear movements, higher absolute [HHb], more transverse ears and less left-forward ears than sheep from the predictable, stimulus-rich housing conditions. However, these differences were small. The ratio of between- to within-individual variability was very low indicating little consistency in individual reactions. In conclusion, we found only weak evidence that presumed valence had a consistent effect on the indicator variables for emotional reactions in a given sheep, and these reactions were not modulated by presumed mood. Also, there was little indication that the sheep reacted in a way reflecting an individualised personality.