Short- and Long-Term Effects of Weaning Age on Pig Innate Immune Status

The study was conducted to evaluate short- and long-term effects of pig wean age on innate immunity and cortisol. Seventy-two white crossbred pigs from 12 litters were randomly assigned to a weaning age of 14 or 28 d-of-age. Pigs were weaned at assigned treatment age and kept as littermates until 20 wk-of-age. Blood samples were taken prior to weaning (d 0) and days 1, 7, and 14 post-weaning (short-term), and at 8, 12, 16, and 20 wk-of-age (long-term). Prior to weaning (d 0), total WBC and lymphocyte numbers were greater for 28-d weaned pigs than 14-d and 28-d pigs had greater lymphocyte numbers at d 1, 7, and 14 post-weaning. At d 0, cytotoxicity and phagocytosis were greater for 14-d than 28-d weaned pigs. Regardless of age, at d 1 and 7 post-weaning all pigs had greater WBC counts, neutrophils, and phagocytosis, but reduced lymphocytes and NK cytotoxicity compared with d 0. Cortisol was decreased at d 7 and increased at d 14 post-weaning in 28-d weaned pigs. These pigs also had greater cortisol at d 0, 1 and 14 post-weaning than 14-d weaned pigs. Effects of weaning on leukocyte profile and N:L ratio were longer-lasting in 14-d weaned pigs than 28-d with effects still apparent at d 14 post-weaning for lymphocytes, neutrophils, N:L ratio, NK, phagocytosis, and IgG. These data imply that weaning age differentially affected pig leukocyte populations and innate immunity in response to weaning stress in both short- and long-term. More specifically, pigs weaned at 14 d-of-age had a more profound and longer-lasting stress response to weaning and 14-d weaned pigs had a more profound innate response, especially NK cytotoxicity while 28-d weaned pigs had more profound antibody response (IgG) in the long-term and these responses were still evident at 20 wk-of-age.