Effects of a Low Crude Protein Diet Supplemented With Crystalline Amino Acids on the Laying Performance and Intestinal Health of Laying Hens Challenged With Salmonella Enteritidis

This study was conducted to investigate the impacts of a low crude protein diet on laying performance, intestinal morphology, and tight junction protein gene expression in laying hens challenged with Salmonella enteritidis (S. enteritidis). A total of 144 56-week-old Hy-Line Brown laying hens were randomly allocated into two groups a nonchallenged group (CON) and an S. enteritidis-challenged chicken group (SE, orally administrated 3 ml/hen, 10⁹ CFU S. enteritidis). After 7 days, the SE-infected chickens were subjected to two dietary treatments. The experimental groups included a nonchallenged group fed a diet based on corn-soybean meal (CON, 16.5% crude protein), an SE group fed a diet based on low crude protein (LCP, 13% crude protein) and an SE group fed a normal crude protein diet (NCP, 16.5% crude protein). The results showed that challenge with SE increased the plasma concentrations of lipopolysaccharide (p < 0.05), decreased the relative mRNA expression of ZO-1 (p < 0.05) in the jejunum. In addition, compared with CON, feeding a low-protein diet significantly increased yolk colour, but there was no significant difference in Laying Performance, Plasma Immunoglobulin Levels, Plasma LPS Concentration and Jejunal Morphology and mRNA Expression of Intestinal Barrier Function. Sequencing data of 16S rDNA indicated that there was a tendency for the reduction of bacteroidetes after SE infection (p = 0.06). Compared with the Con group, the Chao1 (p = 0.08), Observed-OTUs (p = 0.08) and faith_pd (p = 0.07) showed a decreasing trend in the LCP group. These results suggest that S. enteritidis infection of laying hens can cause intestinal mucosal damage, LCP can maintain the normal physiological function of laying hens, as well as the NCP group, which helps to save the use of protein feed raw materials.