Analysis of behaviours observed during mechanical nociceptive threshold testing in donkeys and horses

The aims of the study were to analyse and compare behaviours in horses and donkeys observed during nociceptive threshold tests (NTT) with a mechanical stimulus applied to the limb. The purpose was to identify end-point behaviours suggesting the animals had perceived the stimulus to be noxious. Six male castrated horses (aged 3-4 years, weighing 415-503 kg) and eight castrated male donkeys (aged 4-9 years, weighing 152.5-170.5 kg) were studied. Video data recorded during mechanical NTT, were analysed by a single observer. Behaviours were classified into short duration event behaviours, and longer duration activity/state behaviours. Frequency of behaviours within a test (event behaviours) and percentage time spent during the test (activity/state behaviours) were calculated. Data were compared between horses and donkeys using Mann Whitney tests (non-parametric data) or t-test (parametric data). Significance was taken as P<0.05. Behaviours during the tests were observed which could indicate the animals perceived the stimulus as noxious. These included flattening ears back against the head, and turning the head (horses) and chewing (donkeys) although these were not consistent across both species. Foot lifts were often preceded by other behaviours which suggests that the foot lift was not purely a reflex withdrawal response. A shift in weight towards the contralateral limb was a consistent prodromal sign for an end-point foot lift.