Classification of resilience to weaning stress using cortisol patterns and associations with growth and behavior in Yorkshire gilts

The pork industry has recognized a need to develop more robust pigs, and one method to achieve this is through the selection of resilient animals. Resilience can be measured using a proxy variable over time. Our previous work has shown serum cortisol to be a promising potential proxy for measuring resilience in crossbred gilts at weaning. In this study, we replicate and expand on our previous work using serum cortisol response to classify resilience of pigs to weaning stress and investigate differences in growth and behavior in purebred Yorkshire gilts. One stress resilient (SR) gilt and one stress vulnerable (SV) gilt was selected from each of 13 litters at weaning (n = 26). Body weights were measured and average daily gain calculated for suckling stage (birth-4 wk-of-age), weaning at 4 wk-of-age, nursery stage (4-8 wk-of-age), transition to grow-finish at 8 wk-of age, early grow-finish (8-12 wk-of-age), and mid grow-finish (12-16 wk-of-age). Skin lesions were recorded before and after weaning as well as at a mixing event at 8 wk-of-age. To assess behavior, we conducted a dyadic contest at 7 wk-of-age, handling tests at 8 wk and 12 wk-of-age, and a novel object test at 12 wk-of-age. We detected no significant differences in overall growth between SR and SV gilts. However, during the first week post-weaning SR gilts gained twice as much per day as SV gilts (SR: 152 ± 31 g/d, SV: 79 ± 31 g/d, P = 0.06). SR gilts also tended to gain more per day during the first week in grow-finish (P = 0.09). This higher performance relative to SV gilts immediately following change may suggest SR gilts adapt faster to a new environment. No significant differences were detected between SR and SV gilts in skin lesions or behavior in the dyadic contest, handling tests, or novel object test. These results are inconsistent with our previous findings from commercial crossbreed pigs and indicate that classification based on serum cortisol pattern is associated with limited differences in Yorkshire gilts.