The behavioural, physiological and immunological responses of lambs from two rearing systems and two genotypes to exposure to humans

Abstract

The behavioural, physiological and immunological responses of lambs from two rearing systems and two genotypes to exposure to humans was assessed during and immediately after testing in an open-field arena. Ninety-six lambs of two genotypes (Scottish Blackface: BF and Texel×(Blue-faced Leicester×Scottish Blackface): T) were used. From birth to weaning one of two management regimes was applied: extensive (E), whereby animals were handled as little as possible or semi-intensive (I), in which lambs experienced a greater level of human exposure. Eight lambs from each of the four treatment groups received an antigenic challenge ( Mycobacterium a. paratuberculosis) at 9 weeks of age to allow subsequent testing of immunological reactivity. At 1 and 3 weeks after weaning and 1 year later, lambs were tested in groups of four in a 4.5×4.5 m indoor arena, marked with gridlines at 0.75 m intervals. There were a number of occasions where testing revealed significant effects of genotype, management or their interaction, but in an approximately equal number of instances no significant effects of either genotype or management were observed. Genotype significantly influenced the number of squares occupied in the test arena over a 10-min period before the human entered (100.4 vs. 110.5; sed 2.70 for BF and T lambs, respectively, p<0.001). In relation to the number of new squares entered, there was a genotype×management interaction: BFE lambs entered fewer squares than TE lambs but following semi-intensive management (I) BF lambs entered more squares than T lambs ( p<0.05). When a human entered the arena after this 10-min period, while there was a gradual reduction in the number of animals which had not moved over the next 5 min, 66 animals had not moved within the allocated time. Also during this period, BF lambs stood facing the human for significantly longer than T lambs ( p<0.05). At the time of arena testing, 12 lambs from each treatment group were fitted with heart-rate monitoring equipment. There were significant differences in heart rate in relation to period of testing, i.e. before (107.9) or after (112.3) the point at which the human entered the arena or when the lambs were walking in the presence of a moving human (126.3 b.p.m.; sed 2.15, p<0.001). When lambs were alone in the test arena, BF lambs had higher heart rates than T lambs ( p<0.05). The heart rate of E lambs increased more than that of I lambs when the human entered the pen (9.4 vs. 0.3 b.p.m.; sed 3.95, respectively; p=0.05). Immediately following completion of the behavioural tests, blood samples were collected from subsets of lambs. Plasma cortisol concentrations of BF lambs were greater than those of T lambs (82.0 vs. 53.5 nmol/l; sed 10.18, p<0.01) but there was no effect of management. Blood samples collected from the lambs challenged with a novel antigen prior to weaning showed a genotype but not a management effect on both antibody and cell mediated immune responses, although there was a genotype×management interaction. However, it should also be noted that there were no significant effects of either genotype or management on a number of the indices recorded: latency of lambs to move from the initial entry position in the absence or subsequent presence of a human; length of time one individual was separated from the other three; distance moved in a raceway before stopping; plasma β-endorphin concentrations; heart rate in the presence of a human. Overall, these results suggest that although differences in responsiveness associated with specific genotypes of sheep can be detected in a test situation, the early life management regime may also have an effect. The results of this study caution against drawing conclusions between studies where different genotypes are employed.