Social Behaviour in Lambs (Ovis aries) Reared under an Intensive System during the Prepuberty Period

The social behaviour of twenty-one lambs of three sheep breeds (Chios, Karagouniki, and Synthetic) was observed from the age of 2.5–7 months, divided into three equal periods (A, B, C) of 1.5 months each. The frequency of the performed agonistic behaviours was higher (p < 0.01) before four months of age (period A: 11 × 10−4 ± 2 × 10−4) compared to the other periods (B: 5 × 10−4 ± 1 × 10−4; C: 8 × 10−4 ± 1 × 10−4). The same was noticed for affiliative behaviours performed (A: 21 × 10−4 ± 3 × 10−4; B: 8 × 10−4 ± 1 × 10−4; C: 5 × 10−4 ± 1 × 10−4), and for agonistic and affiliative behaviours received (p < 0.001). The lambs had higher levels of wool cortisol (23.398 ± 5.344 pg/mg; p < 0.01) at period C compared to A (7.899 ± 1.19 pg/mg). Breed affected the affiliative behaviours. Karagouniki showed higher frequencies than Synthetic (16 × 10−4 ± 3 × 10−4 vs. 6 × 10−4 ± 1 × 10−4). Blood cortisol was higher (p < 0.05) in the Synthetic (4.789 ± 0.928 ng/mL) compared to the Chios (1.805 ± 0.417 ng/mL) breed. Overall, lambs’ behaviour displayed changes upon time, with four months of age being a step to a next developmental stage with fewer social interactions and higher levels of cortisol.