Background: Since transport evokes physiological adjustments that include endocrine responses, the objective of this study was to examine the responses of circulating beta-endorphin, adrenocorticotrophic hormone (ACTH) and cortisol levels to transport stress in stallions.
Methods: Forty-two healthy Thoroughbred and crossbred stallions were studied before and after road transport over distances of 100, 200 and 300 km. Blood samples were collected from the jugular vein: first in a single box immediately before loading (pre-samples), then immediately after transport and unloading on arrival at the breeding stations (post-samples).
Results: An increase in circulating beta-endorphin levels after transport of 100 km (P < 0.01), compared to basal values was observed. Circulating ACTH levels showed significant increases after transport of 100 km (P < 0.001) and 200 km (P < 0.001). Circulating cortisol levels showed significant increases after road transport over distances of 100, 200 and 300 km (P < 0.001). An effect of transport on beta-endorphin, ACTH and cortisol variations was therefore evident for the different distances studied. No significant differences (P > 0.05) between horses of different ages and different breeds were observed for beta-endorphin, ACTH and cortisol levels.
Conclusion: The results obtained for short term transportation of stallions showed a very strong reaction of the adrenocortical system. The lack of response of beta-endorphin after transport of 200-300 km and of ACTH after transport of 300 km seems to suggest a soothing effect of negative feedback of ACTH and cortisol levels.