Assessment of sociability in farm animals: The use of arena test in lambs

The present study aimed to evaluate an experimental approach to individually assess social reactivity among sheep. INRA401 male lambs (n = 163) were reared together outdoors as part of a larger flock. Fifteen days after weaning the animals were individually exposed to an arena test of 2 phases (1-social attraction, 2-social isolation) during which proximity toward conspecifics and vocal and locomotor reactivity were measured. One day after the test their inter-individual distances were measured when grazing over a 2-h period in order to estimate their sociability on pasture. This was made using scan sampling recording the identity of the nearest neighbour for each individual, which led to the establishment of a sociability index. Overall, we found that high-pitched bleats recorded during the attraction phase (r = 0.22) and the isolation phase (r = 0.23) of the arena test as well as the locomotor activity measured during the isolation phase (r = 0.27) were positively correlated with the sociability index. Furthermore, the behaviour of lambs during the isolation phase of the arena test (i.e. vocal and locomotor agitation) appeared to be a significant predictor explaining 13% of the variance of the sociability on pasture. The behavioural reactivity measured through the arena test thus reflects at least to some extent the sociability of sheep. Those results are very encouraging as they suggest that the sociability of lambs could indeed be evaluated through a short experimental test, which is less time consuming than field ethological observations.