Associations between skin lesion counts, hair cortisol concentrations and reproductive performance in group housed sows

The effects of acute stress on sow reproductive performance are well established, but we know less about the implications of chronic stress for sow performance. This study investigated associations between total skin lesion counts 24hr and 3 weeks post-mixing, hair cortisol concentrations at the end of pregnancy, and reproductive performance of sows. Sows (n = 264; parity 1-5) were artificially inseminated and locked into individual feeding stalls within 11 fully slatted gestation pens, immediately after service. Sows were released from the stalls at approximately 25 days post-service, allowed to mix, and thereafter had free access to the stalls. Skin lesions were counted 24hr post-mixing (i.e. one day after release from the stalls), and 3 weeks post-mixing on the anterior (head, neck, shoulders and front legs), middle (flanks and back), and posterior (rump, hind legs and tail). The sum of counts across all sites yielded a total skin lesion count for each sow. Back fat depth measurement and hair collection were carried out one week prior to farrowing. Sow reproductive performance measures included the number of piglets born alive, born dead, mummified, and total born. Piglets from 75 sows were tagged, weighed and scored for vitality (0 = least vital, to 4 = perfect) and intra-uterine growth retardation (IUGR; 0 = none, to 3 = severe). There was a positive association between total skin lesion counts 3 weeks post-mixing and both the number of mummified piglets (P = 0.045), and IUGR scores (P = 0.018). There was no correlation between total skin lesion count either 24hr (Rho = 0.10; P > 0.05) or 3 weeks post-mixing (Rho = -0.02; P > 0.05) and hair cortisol concentrations. There was also no association between hair cortisol concentrations and measures of sow reproductive performance (P > 0.05). Higher skin lesion counts 3 weeks post-mixing were associated with aspects of sow reproductive performance. This suggests that chronic stress caused by sustained aggression had a negative impact on the reproductive system. Nevertheless, given the lack of significant associations between hair cortisol, skin lesion counts, and measures of reproductive performance, this was not supported by the findings for hair cortisol.