Effect of dietary supplementation of mannan-oligosaccharides on performance, blood metabolites, ileal nutrient digestibility, and gut microflora in Escherichia coli-challenged laying hens.

The present study was carried out to investigate the effect of dietary supplementation of different levels of mannan-oligosaccharides (MOS) on performance, egg quality, immune responses, and gut microflora in laying hens exposed to Escherichia coli (E. coli) challenge. A total of 180 Hy-Line W-36 laying hens, 55 wk of age, were randomly distributed among 5 dietary treatments with 6 replicates of 6 hens each. Experimental diets consisted of 5 graded levels of MOS (0, 0.05, 0.1, 0.15, and 0.2% of diet). The study lasted 77 d including 7 d for adaptation and 70 d as the main experimental period subdivided into two 35-d periods. The results showed increases (P<0.05) in egg production percentage and egg mass, and a decrease (P<0.05) in feed conversion ratio (FCR) in birds fed the diets containing 0.1 and 0.15% MOS compared with control birds during the first 35-d period. In addition, there were significant differences between dietary treatments for egg mass and FCR during the second 35-d, with the best (P<0.05) values observed for hens fed on 0.1% MOS-supplemented diet. Feed intake and egg weight, however, were not influenced by dietary treatments throughout the experimental period. Compared to control birds, supplemental MOS resulted in 9.8% (P<0.01) and 8.1% (P<0.05) increases in hen-day egg production and egg mass, respectively, during the entire experimental period. Dietary supplementation with 0.1 to 0.2% MOS decreased (P<0.01) serum triglycerides concentration compared with control birds. In addition, serum concentration of low-density lipoproteins was reduced (P<0.001) by all supplemental MOS levels. In contrast to Newcastle antibody titer, primary antibody response against sheep red blood cell was significantly (P<0.05) affected by supplemental MOS. Supplementation of MOS into the diet caused increases in digestibility coefficients of DM (P<0.05) and CP (P<0.01). In addition, there was a significant (P<0.01) difference between dietary treatments for ileal ether extract digestibility, with the highest digestibility values assigned to the hens supplemented with 0.05% MOS. Although dietary MOS supplementation had no effect on ileal E. coli and total bacteria enumerations, it resulted in a decrease (P<0.01) in Salmonella count and increased Lactobacillus. The present findings indicate that MOS supplementation of laying hens under bacterial challenge could improve productive performance probably through modification of intestinal bacterial populations and improving nutrient digestibility.