Severe claw lesions in pregnant sows reduce prolificacy and increase litter heterogeneity

Abstract Background Claw lesions (CLs) are highly prevalent in sow herds, affecting animal welfare and productivity. This study aimed to evaluate the incidence of CLs in pregnant sows and their impact on litter performance. Additionally, we assessed hair cortisol, cortisone, and oxytocin levels to determine whether CLs cause any stress in sows. The study involved 693 hyper-prolific sows, initially assessed for CLs at farrowing. After weaning, they were housed in individual AI crates, where their hair was shaved. At 28 days post-insemination, pregnant sows were moved to group pens. One week before expected farrowing, sows (n = 507) were transferred to individual farrowing crates where newly grown hair samples were collected, and CLs reassessed. Claw lesion severity was scored from 0 to 3 (SS0: no lesions, SS1: mild, SS2: moderate, SS3: severe). Sows were then classified into 3 categories (CAT): CAT1 (SS0 + SS1), CAT (SS1 + SS2, not SS3), and CAT3 (SS1 + SS2 + SS3). The total number of CL per sow and the final sow score were calculated as the sum of CLs observed on the claws and the sum of all CL severity scores, respectively. Results Only 4,1% of sows had no CLs, while 66.5% exhibited moderate to severe lesions (CAT2+CAT3). Sows from CAT3 had the highest CL number and final sow score (p < 0.05) and presented the worst values for total piglets born, piglets born alive, low-weight piglets born ( < 1 kg), proportion of low-weight piglets born per litter, and mean litter weight at birth. However, stress biomarker levels did not differ among categories and were not associated with litter performance. Conclusions Our findings indicate that severe CLs impair litter performance and increase litter heterogenicity, particularly the incidence of low-weight piglets born. These effects do not appear to be directly linked to stress biomarker levels but may result from behavioral and physiological disruptions affecting animal well-being derived from the presence of severe CLs. Given the significant economic and welfare implications of severe CLs, further research is needed to elucidate their impact on reproduction and to develop effective protocols to better detect stress and pain in affected sows.