Adaptation to weaning in piglets (Sus scrofa domesticus): salivary cortisol and positive behavior as potential indicators

Abstract

Commercial piglets have to deal with a lot of challenges, including weaning. During weaning, piglets are separated from the sow, transferred from liquid to solid feed, and moved to an unfamiliar environment. Piglets should adapt to these changes to maintain a positive welfare state. Both physiological and behavioral outputs may function as indicators of adaptive capacity. The aim of this study was to examine adaptation to weaning stress by assessing cortisol levels and frequencies of positive behavior separately and in combination with each other as potential indicators of adaptation to weaning. Cortisol is frequently used as a proxy for stress, while positive behavior has already been shown to have a short-term adaptive value as a coping behavior. Ninety-six piglets ([Landrace x Yorkshire] x Yorkshire or [Hampshire x Yorkshire] x Yorkshire) were studied from birth to 10 weeks of age in two replicated rounds (R1 and R2, 48 piglets each). Piglets were evenly distributed over enriched and conventional housing systems to induce behavioral variation (48 piglets each). Weaning occurred around 28 days of age. Salivary cortisol levels were measured from samples taken one day pre-weaning and immediately after weaning, whereas behaviors were monitored two to three times weekly by continuous recording from 1.5 to 7 weeks of age. The scored behaviors included play, exploration, and all positive behavior combined, including positive social behavior. The results revealed varying effects of weaning on cortisol and positive behavior per round. In R1, piglets had 58% lower cortisol levels after weaning compared to before weaning (rate ratio = 0.424, 95% confidence interval (CI) [0.335, 0.536]), whereas in R2 piglets had 35% higher cortisol levels after weaning versus before weaning (1.34, 95% CI [1.074, 1.689]). Total positive behavior and exploration frequencies increased by 20% (1.204, 95% CI [1.045, 1.386]) and 28% (1.283, 95% CI [1.122, 1.468]), respectively, after weaning compared to before weaning in R2. In contrast, such an increase was not found for R1, nor for play behavior in both rounds. Moreover, R2 exhibited a 42% reduction in pre-weaning cortisol levels compared to R1 (0.584, 95% CI [0.335, 0.536]), and a 43% decrease in pre-weaning behavior frequencies compared to R1 (0.571, 95% CI [0.485, 0.654]). Furthermore, R1 showed a 3% increase in exploratory behavior frequency per unit increase in cortisol after weaning (1.030, 95% CI [1.009, 1.053]). In conclusion, some evidence for an adaptive response in cortisol and positive behavior and the correlation between both to weaning stress was found. However, this response was not generalizable to all piglets in both rounds. This study highlights the need for caution when interpreting results from replications of the same studies and studies with different experimental designs. Our research provides the first steps in determining whether cortisol and positive behavior together may indicate weaning adaptation.