Becerra_2025_Animals.(Basel)_16_

Weaning is one of the most stressful stages in pig production, especially for Iberian piglets, which grow more slowly than other cosmopolitan breeds and therefore, have a lower weaning weight when raised in intensive systems. Stress at weaning, caused by separation from the sow, dietary change, and regrouping with unfamiliar piglets, can negatively impact welfare, immune function, and performance. Pre-weaning socialization, which allows piglets from different litters to interact before weaning, has been proposed as a strategy to reduce aggression and facilitate the adaptation to the post-weaning period. However, its physiological effects in Iberian pigs remain largely unknown. In this study, 8 Iberian sows and their litters were assigned to either a control group (CTRL) or a socialization group (SOC) where litters were mingled (socialized) two weeks before weaning. Salivary and serum biomarkers of stress, inflammation, immunity and metabolism were measured at weaning (pwD0) and 7 days post-weaning (pwD7), and growth performance was recorded until 60 days of age. Socialized piglets showed reduced salivary Adenosine Deaminase (ADA) activity at pwD0 and pwD7 and lower salivary chromogranin A (CgA) and serum Haptoglobin (Hp) levels at pwD7. In contrast, they presented higher concentrations in serum of high-density lipoprotein (HDL), low-density lipoprotein (LDL), total cholesterol, glucose, and urea at pwD7 compared to controls. Attending to the sex effect, Butyryl-cholinesterase (BChE) serum concentration was higher in males and urea, and creatinine were higher in females. Growth rates were higher in socialized piglets in the first two weeks post-weaning but lower thereafter. These findings may suggest that pre-weaning socialization could reduce the stress associated with early post-weaning in Iberian piglets, thus potentially improving welfare and adaptation during this period.