Research Note: Increase of bad bacteria and decrease of good bacteria in the gut of layers with vs. without hepatic steatosis

Fatty liver hemorrhagic syndrome (FLHS), usually occurring in hens in the late laying period, can lower egg yield and even cause death. Similar to nonalcoholic fatty liver disease in humans, FLHS may begin with simple hepatic steatosis. It is known that gut microbiota is important to the development of nonalcoholic fatty liver disease, but the relationship between FLHS and gut bacteria remains unclear. In this study, bacteria compositions in the ileum and cecum were determined by 16S rDNA sequencing analysis in the groups of hens with vs. without hepatic steatosis (average liver fat contents were 0.34 mmol/g protein or 2.6% vs. 0.84 mmol/g protein or 6.0%). These hens were in the 2 tails of the liver fat content distribution with each tail accounting for 10% of the test population containing 90 66-wk-old healthy Rhode Island Red laying hens raised under routine feeding regimen. The results showed that liver weight but not the weights of the body, heart and abdominal fat were significantly different between the groups. Moreover, bacterial diversity was not significantly different between the groups, but bacterial diversity in the cecum was higher than that in the ileum. Proteobacteria was the most dominant phylum in the ileum, whereas Proteobacteria, Firmicutes, and Bacteroidetes were the most dominant phyla in the cecum. Some bacteria were common to the ileum and cecum, but some were unique. Furthermore, some bacteria were significantly different in abundance between the groups, that is the group without hepatic steatosis had more bacteria inhibiting host energy absorption or benefiting intestinal health, whereas the group with hepatic steatosis had more conditionally pathogenic or harmful bacteria. In conclusion, hepatic steatosis in laying hens is associated with intestinal bacterial composition (bacterial abundance) but not bacterial diversity. The identified common and unique bacteria are related to the functional characteristics of the ileum and cecum. The decrease of beneficial bacteria and the increase of harmful bacteria in the intestine of laying hens may increase FLHS incidence by promoting hepatic steatosis.