The gastrointestinal tract is lined by continuous epithelial cells which not only digest and absorb nutrition, but also maintain the physical and functional barrier to unhealthy luminal antigens. Weaning piglets are abruptly forced to combined stressors, such as removal from sow and littermates, transportation to a new environment and abrupt changes in diet. Early weaning stress in the pig induces immediate and long term harmful effects on intestinal defense mechanisms including lasting disturbances in intestinal permeability and morphology, increased electrogenic ion transport, and decreased digestive and absorptive capacity.

Tight junction proteins form a dynamic seal between epithelial cells, forming a barrier that regulates the permeability of ions, macromolecules, and cells through the paracellular pathway. And the activity of voltage-gated K⁺ (Kv) channels controls membrane potential.

Researchers in the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) used sixty-four neonatal piglets from eight litters (eight piglets per litter). Some piglets were be nursed by sows till to 21 days old, whereas other piglets were weaned at 14 days old and housed the same farrowing cage without sow and fed with creep feed. Eight piglets were slaughtered from each litter at 1, 7, 14, 21 day of age and on 1, 3, 5, 7-day after weaning. They employed hematoxylin-eosin staining, scanning electron microscopy, real-time quantitative, and assay kit to observe the intestinal morphology, the expression of tight junction proteins and Kv, and activity of brush enzyme.

The team found that the most serious damage of intestinal morphology and barrier induced by early-weaning at 14 day of age occurs on day 3 or 5; there is an adaptive restoration on day 7 post-weaning, but does not return to the pre-weaning levels that showed impairment of intercellular junctions and Kv channels.

"The microvilli of the jejunum on postnatal day 1 were long, thin and sparse, and then grew shorter, stouter and denser with age in the present study, which was associated with an in-crease in the goblet cell number, which indicates an increase in the absorption area of the intestinal mucosa," said WANG Jing, a doctoral researcher at ISA. A large luminal surface area with optimal enterocyte functional maturity is important for young growing pigs so that they may attain their maximum digestive and absorptive capability. "Meanwhile, cell proliferation, alkaline phosphatase (AKP) activity (a kind of brush enzyme in the intestine) and intercellular junction protein expression of small intestine gradually increased in association with the mucosal maturation from day 1 to 21 in suck-ling piglets."

Early weaning stress impairs the intestinal histological morphology, inhibits the proliferation and differentiation of intestinal epithelial cells, and increases the permeability of intestinal barrier. Weaning at day14 of age induced an increase in the intestinal permeability and intestinal Kv channel expression, but a decrease in villus height/crypt depth, cell proliferation, AKP activity and the expression of intercellular junction proteins in the small intestine. These results should help to improve the adaptation to weaning in piglets. The promotion of intestinal maturation and epithelial restitution may help to alleviate the adverse effects of weaning.

This research was funded by the National Key Basic Research Program of China(2013CB127302), National Natural Science Foundation of China (31330075,31372326, 31301988, 31301989), the State Key Laboratory of Animal Nutrition(2004DA125184F1401), the Spark Program of Jiangxi Province (20142BBF061051)and Changsha Lvye Biotechnology Limited Company Academician Expert Workstation, Guangdong Wangda Group Academician Workstation for Clean Feed Technology Research and Development in Swine, Guangdong Hinapharm Group Academician Workstation for Biological Feed and Feed Additives and Animal Intestinal Health.

The study entitled "Developmental changes in intercellular junctions and Kv channels in the intestine of piglets during the suckling and post-weaning periods" has been published in the January issue of Journal of Animal Science and Biotechnology, details could be found at http://jasbsci.biomedcentral.com/articles/10.1186/s40104-016-0063-2.