Noise and vehicular motion as potential stressors during the transport of sheep
During three journeys of 15 h in a lorry and two sets of experiments in a trailer, the relative importance of ambient noise and vehicular motion were assessed by measurements of salivary cortisol concentration, heart rate and behaviour. Mean sound levels in the lorry were approximately 96 dbA with occasional episodes at 103 dbA. Vehicular motion was assessed in terms of numbers and magnitude of acceleration events registered by a triaxial accelerometer. The three lorry journeys showed, respectively, that heart rate was correlated with vehicular motion when sheep were loosely stocked (0.41 m2 per sheep) but not when they were tightly stocked (0.28 m2 per sheep); that heart rate sometimes tended to increase when ambient sound was greater and that the effect of sound was not as consistent as that of vehicular motion. In the first trailer experiment, salivary cortisol response was the same whether sheep confined in a quiet stationary trailer (60 dbA) were or were not exposed to extra noise (90 dbA) while heart rate was higher in the former condition. In the second trailer experiment when the trailer was being towed on public roads with or without extra noise (92.3 and 100.5 dbA respectively), heart rate and salivary cortisol concentration were both elevated compared with control sheep in a pen but the extra noise had no consistent effect. The sheep showed no orientation away from the noise source, nor was there any difference in their expression of a behaviour (standing with the head below the level of the shoulders) which could indicate discomfort. Hence vehicular motion can result in poor welfare in sheep, especially at loose stocking density but ambient noise was not found to have a consistent effect.