Assessing pharmacological models of anxiety in sheep (#674)
The use of pharmacological models can be helpful when trying to understand the origin of specific behaviours and to validate measures of animal welfare. In the current study 12 sheep (8-month-old merino ewes) received an intramuscular injection of 1-(m-chlorophenyl)piperazine (m-CPP; 1 mg/kg), an anxiogenic aimed at causing increased agitation and distress; 12 received an intravenous injection of diazepam (DZP; 0.1 mg/kg), an anxiolytic aimed at reducing agitation-related behaviours; and 11 sheep acted as a control (C; saline). Thirty minutes after treatments, behavioural tests were performed on each sheep individually: general movement (time taken to move along a 150 m race way); behaviour in an isolation box, evaluated by the number of steps, 180º turns and vocalisations made; and feeding motivation. The m-CPP sheep took significantly more steps than the control sheep while in isolation, and DZP sheep tended to take more steps than the controls (steps m-CPP=9.1, C=5.4 and DZP=7.1; m-CPP vs. C p<0.001; C vs. DZP p=0.08). The m-CPP treated sheep performed more 180º turns than the other groups (m-CPP=5.9, C=3.3 and DZP=4.3, p=0.004). No significant differences were identified between the treatments for vocalisations during isolation (m-CPP=5.0, C=7.1 and DZP=5.9), general movement (m-CPP=61 s, C=57 s and DZP=63 s), or feeding motivation (number of sheep to feed during the test: m-CPP=7, C=9 and DZP=9). During isolation, which is a particularly strong stressor to sheep, it appears that m-CPP treated sheep showed greater levels of anxiety which was displayed through increased movement. The usefulness of DZP as a model of low anxiety in sheep was not clear; the dosage may need modification and/or the behavioural tests used in this study may not identify low anxiety effectively. The current study suggests m-CPP is a useful anxiogenic, but results were not able to determine the effectiveness of DZP in reducing anxiety.