Intestinal morphology and immune profiles are altered in piglets by early-weaning

This study was to investigate the developmental changes in intestinal morphology and immune profiles in suckling and weaning piglets. Seventy-two weaning piglets with equal initial body weight from 8 litters (Duroc x Landrace x Yorkshire, 9 piglets per litter) were selected. Thirty-two piglets in the suckling group were nursed by sows until they were 17, 21, 28, or 35 days of age. While the other forty piglets were weaned at 14 d of age, and then housed in the same farrowing cage without a sow and slaughtered until they were on d 0, 3, 7, 14 and 21 after weaning at d 14 of age (wd 0, 3, 7, 14, 21). Blood, jejunal mucosa, intraepithelial lymphocyte (IEL) and lamina propria T lymphocyte (LPL) were harvested from suckling piglets at d 14, 17, 21, 28 and 35 of age and weaning piglets on d 0, 3, 7, 14 and wd 0, wd 3, wd 7, wd 14 and wd 21). The results showed that compared with the wd 0, early weaning significantly declined the average daily gain of postweaning 0-7 (wd 0-7) (P < 0.05), and jejunal villus height on wd 3 (P < 0.05), as well as increased the jejunal crypt depth of piglets on wd 7, 14 and 21 (P < 0.05). And there were no significant differences in average daily gain and villus height after suckling (P > 0.05). The level of serum interferon-gamma (IFN-gamma) was increased on wd 7 and decreased on wd 21 (P < 0.05), while IFN-gamma level in jejunal mucosa was enhanced at wd 3 in comparison with wd 0 (P < 0.05). And the serum interleukin-4 (IL-4) levels were increased at wd 14, wd 21, but the mucosa IL-4 concentration was strikingly increased on wd 7 (P < 0.05). Moreover, weaning led to the enhanced levels of interleukin-1b (IL-1b), interleukin-2 (IL-2) and soluble interleukin-2 receptor (sIL-2R) in serum (P < 0.05), as well as declined the levels of sIL-2R in jejunal mucosa at wd 3 (P < 0.05). In suckling piglets, the serum immunoglobulin A (IgA), IL-4 and IL-2 levels were increased with increasing age (P < 0.05), whereas the jejunal mucosa IL-1b and serum sIL-2R levels were lower (P < 0.05). Furthermore, significantly lower CD4 percentage in peripheral blood T lymphocyte subsets were found at wd 3 and wd 7 (P < 0.05), whereas the CD8 percentage in peripheral blood T lymphocyte subsets were enhanced on wd 3 and wd 7 than wd 0 (P < 0.05). Moreover, the weaning piglets at wd 3 had a lower CD4/CD8 ratio than wd 0 (P < 0.05). Additionally, we found that weaning decreased IgG, IL-4, IL-2 and IL-1b levels of IEL during 1-week post-weaning (P < 0.05). Similarly, the levels of IgA, IgG, IL-2 and sIL-2R in LPL medium were also declined from piglets postweaning 1 week (P < 0.05). Early weaning reduced the growth performance, damaged jejunal morphology, disrupted IFN-gamma/IL-4, IL-2/sIL-2R and T lymphocyte balance, and impaired the IEL and LPL immune profiles of piglets.