Interleukin-15(IL-15) is a cytokine highly expressed in skeletal muscle. The objective of the present study was to investigate the development of muscle IL-15 expression in suckling piglets and in early weaning piglets(day 14) at each level, that is, mRNA, protein, and secretion. Eight litters(eight piglets per litter) of newborn healthy piglets(Large × White × Landrace) with a similar initial weight(1618.0 ± 140.1 g) were chosen and divided into two groups, Group one used suckling piglets that were killed, respectively, at days 1,7,14,21, and group two used early(day 14) weaning piglets that were killed respectively, at days 15, 17, 19, 21. In group one, IL-15 gene expression levels increased significantly(P < 0.05) along with increased body weight over time. IL-15 protein expression levels in piglets at day 21 of age were higher(P < 0.05) than those in piglets at other ages, and there was no difference(P > 0.05)among piglets at other ages. These findings indicated that increased IL-15 mRNA expression did not result in a corresponding increase of its protein expression. In group two, which used early weaning piglets from days 15-19, IL-15 mRNA and protein expression levels increased constantly(P < 0.05) and were higher(P < 0.05) than those in suckling piglets. Moreover, there was no gain of body weight(P > 0.05) compared with suckling piglets at day 14 of age. However, IL-15 protein expression levels in early weaning piglets at day 21 of age dropped significantly(P < 0.05) to the levels as suckling piglets at day 21 of age, while body weight increased(P < 0.05) markedly to the levels as suckling piglets at day 21 of age. In both groups, the serum IL-15 levels of piglets decreased significantly(P < 0.01) over time. Taken together, our results indicate that IL-15 expression differs in suckling piglets and in weaning piglets. It is speculated that IL-15 may play an important role in counteracting the effects of early weaning stress.
