Effects of haloperidol, a dopamine D2 receptor antagonist, on feather pecking behaviour in laying hens

Abstract

Two experiments investigating general behavioural activity and specific pecking behaviour in laying hens under the effect of a dopamine D2 receptor antagonist, haloperidol, were performed. In experiment 1, a total of 240 White Leghorn hens aged 70 weeks were housed in 30 floor pens. Fifty-five of these hens acted as subjects in a dose-response experiment. Behaviour was recorded 30 min before and 30 min after injection of haloperidol or saline. The changes in behaviour were corrected for the effect of saline treatment. The results showed that doses of 0.05, 0.10, 0.20 and 0.50 mg haloperidol/kg body weight (BW) did not give any clear sedative effect, while 1.0 mg haloperidol did so. Thus, the sedative effect seemed to arise at a dose between 0.50 and 1 mg haloperidol/kg and it was concluded that 0.50 mg haloperidol/kg could be used in White Leghorn hens without inducing sedation. In experiment 2, a total of 48 ISA Brown hens aged 118 weeks were used as subjects. The birds were paired with 82-week-old White Leghorn hens chosen at random from an experimental line selected against feather pecking and housed in battery cages. Feather pecking and aggressive pecking were recorded for a period of 50 min before and 50 min after injection of either saline or 0.50 mg haloperidol/kg BW. Feather pecking, but not aggressive pecking, was significantly reduced in the haloperidol treatment (from 1.7 to 0.29 bouts per bird/h, Mann–Whitney U-test N=18, P<0.05; 10.1 to −2.7 pecks per bird/h, P<0.001). The negative value was due to correcting for effect of injection. The results supported our hypothesis that feather pecking behaviour in the adult hen is influenced by dopamine.