Award Talk: Developmental Impacts of Early-life Rearing Environment and Handling on Growth Performance, Immune Activity, and Stress Responses in Pigs

Stressors are stimuli that disrupt physiological homeostasis, and exposure to stress during early life can influence the maturation of neuroendocrine, immunological, behavioral, and physiological stress responses. In pigs, early experiences involving maternal environment and caregiver interaction occur during a critical developmental window and can result in lasting negative effects. Therefore, this study examined how early-life stressors impact growth, immune function, circulating cortisol, coping strategies, and behavior in young pigs. This study utilized a 2 × 2 factorial arrangement including rearing environment [sow-reared (SR) or artificially-reared (AR)] and handling (handled for 2 minutes per day or handled once a week) as experimental factors. Therefore, 72 pigs (n = 38 gilts and 34 boars) were allotted on postnatal day (PND) 2 to 1 of 4 treatments based on litter of origin and body weight (BW): 1) SR-D (sow-reared, daily handling); 2) SR-W (sow-reared, weekly handling); 3) AR-D (artificially-reared, daily handling); and 4) AR-W (artificially-reared, weekly handling). Artificially-reared pigs were housed individually with ad libitum access to milk replacer, while sow-reared pigs were group-housed with their littermates and received all nutrients from the sow. On PND 21, rearing environment and handling interventions ended, and pigs were transferred to nursery pens according to treatment group. Body weight was recorded according to the assigned handling treatment from PND 2-21 and subsequently measured weekly and analyzed on a pen basis from 21-35. The study concluded on PND 35 following euthanasia of all pigs. Data were analyzed using a 2-way ANOVA with the MIXED procedure of SAS. During PND 2-21, AR pigs had greater (P < 0.05) BW gain than SR pigs and subsequently had higher BW on PND 21 and 35. However, SR pigs exhibited improved (P < 0.05) feed efficiency during PND 21-35 compared with AR pigs. The AR pigs displayed elevated (P < 0.05) cortisol on PND 7 and 28 but had decreased (P < 0.05) cortisol concentrations on PND 22, compared with SR pigs. On PND 35, daily-handled pigs had increased (P < 0.05) duodenal mRNA expression of TNF-α, ZO-1, and occludin compared with weekly-handled pigs, while AR pigs had increased ileal (P < 0.05) IFN-γ and IL-1β expression compared with SR pigs. During a tonic-immobility test to assess stress resiliency, AR-W pigs had the longest (P < 0.05) latency to first escape attempt compared with all other treatments. Handling effects were observed during the human approach test, as W pigs had the longest (P < 0.05) latency to approach compared with D pigs. Following the transition to group housing, AR-D pigs spent more (P < 0.05) time nosing conspecifics than SR-D and AR-W pigs. In conclusion, early-life rearing environment and handling frequency influenced pigs’ growth, immune response, behavior, and cortisol concentrations.