PLASMA-LEVELS OF BETA-ENDORPHIN AND IN-VITRO LYMPHOCYTE-PROLIFERATIONAS INDICATORS OF WELFARE IN HORSES IN NORMAL OR RESTRAINED CONDITIONS

Plasma beta-endorphin levels and lymhocyte proliferation were measured in 14 geldings to evaluate the animals' response to different challen ges (application of a lip twitch for five minutes and restraining the animals blindfolded for two hours). The basal beta-endorphin levels sh owed a great variability among the horses, but were consistent for the basal levels measured on different days for each animal. A significan t effect of age on beta-endorphin concentration was found (p=0.005). T he beta-endorphin levels showed an increase after the use of the lip t witch (p=0.0001) and returned to the pre treatment values within 30 mi nutes after the release of the animal. Plasma beta-endorphin levels at the end of the blindfold treatment were lower than basal levels (p=0. 025) and there was a decrease in the proliferation of lymphocytes (p=0 .00001). A negative correlation was found between plasma beta-endorphi n levels and lymphocyte proliferation for individual horses in samples taken before (rho=-0.62; p=0.039) and two hours after the application of the hood (rho=-0.59; p=0.049).