The effect of infection with the abomasal nematode, Haemonchus contortus, on the avoidance behaviour of sheep in a motivational-choice test
1997
Adams, D.B. | Fell, L.R.
The behaviour of immune and non-immune sheep infected with H. contortus and undergoing a variety of experimental treatments was investigated in a motivational-choice test, the arena test. This test evaluates motivational state in sheep by pitting the motivation of test animals to approach a small flock of sheep against the motivation to avoid a human decoy located directly in front of the small flock. Approach distance is decreased by infection in immune ewes but was unaffected by infection in non-immune weaner lambs in the present study. Experimental drug-treatments with the opiate-antagonist nalorphine, the antihistamine chlorpheniramine, and the immunosuppressive glucocorticoid dexamethasone, affected avoidance behaviour but did not shed light on possible mechanisms involved in the changes observed when immune sheep are infected with the parasite. These substances may affect motivational state directly and not through a pharmacological action on processes triggered by infection in immune sheep. Arena tests conducted in immune ewes at 4, 7 and 11 days after challenge infection showed a fluctuating locomotor behaviour, which may arise from either the dynamics of a standard secondary immune response or particular antigens released during larval development. The immune-mediated changes in behaviour in the arena test will have entailed information-processing or cognitive pathways, but it is not known whether they also involved the physiological manifestations of emotion.
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