FALL AND WINTER HORMONE CONCENTRATIONS RELATED TO STRESS IN PIGS IDENTIFIED AS NORMAL AND CARRIER FOR STRESS SUSCEPTIBILITY

Stress is associated with significant losses in the swine industry. Se asonal changes have been shown to affect stress resistance in several species of animals. In the present study, we examined the effect of tw o seasons (fall or winter) on plasma insulin, cortisol, and adrenocort icotrophin hormone (ACTH) levels from fasted normal and carrier pigs f or stress susceptibility when submitted to a blood-sampling stressor b etween 10:00 and 11:00. Comparisons were made of 10 diurnally active n ormal (NN) and 8 carrier (Nn) pigs reared in the fall to 9 NN and 10 N n pigs reared in the winter. The lightdark cycle throughout the period of the experiment was 10h light/14h dark, with lights on from 07:00 t o 17:00. Feed consisted of the traditional western Canadian swine rati on consumed ad libitum. Results revealed significant season-by-genotyp e interactions for plasma insulin and ACTH concentrations in response to the blood-sampling stressor. The normal pigs displayed a significan tly lower plasma insulin level during winter compared to the fall seas on. Plasma ACTH of normal pigs was 18% lower in the winter compared to the fall season, although this difference was not statistically signi ficant. The carrier genotype, on the other hand, demonstrated higher p lasma insulin concentration and lower plasma ACTH concentration in the winter compared to the fall season. Furthermore, there was a main gen otype effect in plasma cortisol concentration such that the carrier pi gs experienced a greater level compared to the normal genotype. Simila rly, the carrier pigs had a more acute ACTH response to the blood-samp ling stressor compared to the normal pigs during the fall season. Resu lts have demonstrated that these two seasons of the year affect the re sponse of both genotypes to a blood-sampling stressor, with the carrie r genotype experiencing a more intense stress reaction in the fall sea son. These results further contribute to the recent research indicatin g that carrier pigs for stress susceptibility have a unique stress res ponse.