Transport stress in horses: an electromyographic study on balance preservation

In order to validate the hypothesis that horse transport stress might also be the result of efforts spent in balance preservation, heart rate (HR) and muscular activity (MA) were analysed in eight Warmblood horses, with respect to individual rest reference values. Electromyographic (EMG) data were collected from Splenius muscles (left and right side), as representative of body anti-gravitational activities. The EMG data performed during each balancing effort were firstly quantified and then reported as percentage of the activity in respect to basal EMG signals obtained during resting; before loading the animal. These data were correlated with the HR recorded at the same time. Moreover, a videotape, synchronised with the EMG and HR data, was made to better recognise and to distinguish the muscular activities necessary for the preservation of balance, from the other muscular activities performed (e.g. searching, scratching, etc.). Although horses displayed HR and EMG individual quantitative differences (in power and number of events), the regression analysis showed that these two electrophysiologic parameters were strictly correlated in all animals. It was concluded that: (a) EMG and HR data can be used to evaluate efforts to preserve the animal’s balance and that (b) this kind of effort might be considered one of the main transport stress factors. Consequently, we deduced that the efforts spent by the animals for a continuous postural adjustment can be considered as a physical expression of both muscular and emotional stress related to road conditions (traffic and/or physical road conditions) and the driver’s specific driving ability. Ó 2002 Elsevier Science B.V. All rights reserved.