Abstract
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.
Highlights
Weaning is a common stressful event in the life of a pig that involves abrupt social, nutritional, and environmental aspects, which may lead to low feed intake, weight loss, increased mortality and potentially compromised health
It has been shown that as weaning age progresses, the immune system develops, such that leukocyte populations shift from cells predominately involved in innate immune function at 14 d-of-age to cells predominately involved in adaptive immune function at 21 and 28 d-of-age implying that weaning age had short-term effects on endocrine and immune measures in pigs [14]
Prior to weaning (d 0 = treatment weaning age), total white blood cell (WBC) and lymphocyte counts were greater for 28-d pigs compared with 14-d pigs (P < 0.05; Table 1)
Summary
Weaning is a common stressful event in the life of a pig that involves abrupt social, nutritional, and environmental aspects, which may lead to low feed intake, weight loss, increased mortality and potentially compromised health. Various factors such as sex, age, previous experience, and genetics, just to name a few, can influence the stress responsiveness of an animal and the biological consequences [1]. The objectives of this study were to identify and describe the short- and long-term impacts of age at weaning on stress responsiveness and immune status of the pig
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