Total darkness activated intestinal clock system and improved intestinal barrier function in growing rabbits.

The aim of study was to investigate the effects of dark environment on production performance, intestinal barrier function and clock-related gene expression in rabbits. Forty weaned rabbits with similar body weight (35-day-old) were randomly divided into 2 treatments (20 replicates per treatment, 1 rabbit per replicate: normal light group (12 L and 12 D) or total dark group (24 D). The experimental period lasted for 10 days, with an adaptation period of 3 days and a subsequent formal experimental period of 7 days. The results showed that feed-to-weight ratio of rabbits in total dark group was significantly decreased compared with normal light group. Dark treatment significantly increased gene expression of claudin-1, mucin1 in duodenum, occludin-1, claudin-1, zona occludens 1 (ZO1), junctional adhesion molecule 2 (JAM2) and interleukin 10 (IL10) in jejunum, claudin-1, mucin1, ZO1 and IL10 in ileum and clock, melatonin 1 A, melatonin 1B, and period1 in cecum compared with normal light group. Total dark treatment increased alpha diversity via increasing chao1 index, observed species index and faith_pd index of cecal flora. Total dark treatment significantly reduced percentage of Deferobacterium at phylum level in cecum, but significantly increased percentage of Rumenococci at genus level. There is an insignificant increasing tendency of acetic acid and propionic acid content of soft feces in total dark group. In conclusion, total dark treatment improves feed conversion efficiency in rabbits and activates cecum clock system, which increased diversity of bacterial flora and production of short-chain fatty acids, then increases intestinal barrier function.