Manipulating early-life environment and handling alters growth trajectories, immune and stress responses, clinical indicators, and intestinal health in young pigs.

Stressors are factors that disrupt homeostasis; in pigs this includes challenges in sow management, human interaction, and weaning. These typically occur in the first month of life, compromising welfare and decreasing growth and increasing mortality. This study investigated the impact of early-life stressors on pig growth, immune response, and coping ability. The study utilized a 2 × 2 factorial arrangement with factors including rearing environment [2 levels; sow-reared (SR) or artificially-reared (AR)] and handling (2 levels; handled for 2 min daily or weekly). Therefore, 72 pigs (38 gilts and 34 boars) were allotted to 1 of 4 treatments on postnatal day (PND) 2 based on their litter of origin and body weight (BW): 1) SR-W (sow-reared, weekly-handled); 2) SR-D (sow-reared, daily-handled); 3) AR-W (artificially-reared, weekly-handed); and 4) AR-D (artificially-reared, daily-handled). AR pigs were housed individually with ad libitum access to reconstituted milk replacer, while SR pigs were group housed and received all nutrients from the sow. On PND 21, rearing environment and handling interventions ended, and pigs were transferred to group nursery pens according to their original treatment assignment. One week later, on PND 28, all pigs received a 5ug/kg of BW injection of lipopolysaccharide to stimulate an innate immune response. On PND 35, all pigs were euthanized to permit sample collection. Data were analyzed using a 2-way ANOVA via the MIXED procedure of SAS. During PND 2-21, AR pigs had greater (P < 0.05) BW gain than SR pigs. Consequently, AR pigs had the heaviest (P < 0.05) BW on PND 21 and 35 compared with SR pigs. However, SR pigs exhibited higher (P < 0.05) feed efficiency during PND 21-35 compared with AR pigs. As a classic marker of stress, fecal secretory immunoglobulin A concentrations were highest (P < 0.05) in SR pigs compared with AR pigs on PND 21. On PND 35, daily-handled pigs exhibited longer (P < 0.05) small intestinal tract length than weekly-handled pigs. Furthermore, SR pigs had increased (P < 0.05) absolute and relative ileal weights, but lower (P < 0.05) absolute duodenal mass compared with AR pigs. Lastly, daily-handled pigs displayed increased (P < 0.05) TNF-α, IL-1β, and occludin mRNA expression relative to weekly-handled pigs, while AR pigs had increased (P < 0.05) mRNA expression of IFN-γ and IL-1β compared with SR pigs. In conclusion, early-life rearing environment and handling frequency influenced growth, immune and stress response, clinical indicators, and intestinal health.