The aim of this study was to examine the effects of diazepam, an anti-anxiety drug, on the fear responses of sheep and its usefulness as a pharmacological method to study welfare. Fourteen, eight month old Romney ewes were randomly assigned to two treatments and injected via jugular venepuncture with diazepam (0.37mg/kg) or saline (controls) 20 minutes before exposure to a barking dog. Heart rate (bpm) and escape attempts were recorded throughout a 10 minute period before injection (baseline), 20 minutes post injection and 15 minutes following the dog. Average heart rate was lower in diazepam-treated sheep during the first 5 minutes following injection (P<0.01) and was significantly higher (P<0.01) for both diazepam and saline-treated sheep during the 5 minutes following exposure to the dog compared to baseline (+23.1 and +21.5 bpm for diazepam and saline respectively). Heart rate then decreased back to baseline levels during the last 10 minutes. Diazepam-treated sheep tended to have a higher number of escape attempts during the 5 minutes following exposure to the dog (P=0.08) compared to controls, suggesting that diazepam may have paradoxically increased anxiety in some sheep. The lack of differences between treatments suggests that diazepam did not modify the fear response of sheep to a dog. There appear to be interpretive difficulties associated with dose rates and the appropriate fear model in the use of diazepam to study anxiety in sheep.
Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 232-236, 2007
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