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Feather pecking in laying hens is a serious behavioral problem that is often associated with feather eating. The aim of the first study was to investigate the influence of ingested feathers on the gut microbiome and its metabolism and to identify keratinolytic gut microbiota. Therefore two different diets, with or without 5% ground feathers, were fed to raising Lohmann- Selected Leghorn chicks. They were divided into 3 feeding groups: group A (control), B (5% ground feathers in the diet), and C, in which the control diet was fed until week 12 and then switched to the 5% feather diet to study the effect of time of first feather ingestion. The gut microbiota was analyzed by cultural methods and by denaturing gradient gel electrophoresis of the ileum and cecum digesta. Short-chain fatty acids, ammonia, and lactate concentrations were measured as microbial metabolites.
The concentration of keratinolytic bacteria increased after feather ingestion in the ileum (P < 0.001) and cecum (P = 0.033). Bacterial species that hydrolyzed keratin were identified as Enterococcus faecium, Lactobacillus crispatus, Lactobacillus reuteri-like species (97% sequence homology), and Lactobacillus salivarius-like species (97% sequence homology). Molecular analysis of cecal DNA extracts showed that the feather diet lowered the bacterial diversity indicated by a reduced richness (P < 0.001) and shannon (P = 0.012) index. The pattern of microbial metabolites indicated changes, especially in the cecum. Ammonia concentration and the molar ratio of propionate, i-butyrate, i-valeriate and n-valeriate were higher in pullets with feathers in the diet compared to the controls.
The second study was conducted with adult laying hens of a selected high and a low feather pecking line based on six generations and affirmed in a controlled behavioral study. The number of whole feathers, feather parts and feather particles in the gizzard and the intestinal microbial metabolites (biogenic amines, short-chain fatty acids, ammonia and lactate) in the ileum and ceca were determined.
In the gizzard the number of feather particles was higher in the hens with high pecking activity (P = 0.012). The pattern of intestinal microbial metabolites was affected. Putrescine and cadaverine concentrations were higher in the ileum of the hens with low pecking activity (P < 0.001, and P = 0.012). Ammonia was higher in the ileum and cecum in this line (P < 0.001, and P = 0.004). In the cecum of the laying hens with high pecking activity higher amounts of L-lactate, D-lactate, total lactate, SCFA and higher molar ratios of propionate and n-butyrate were determined (P = 0.007, P = 0.005, P = 0.006, P < 0.001, P < 0.001, and P = 0.034). Acetate, i-butyrate, i-valerate and n-valerate all present higher molar ratios in the cecum of the hens with low pecking activity (P = 0.001, P = 0.003, P = 0.001, and P < 0.001).
It was shown that the intake of feathers lead to an altered composition of the gut microbiota and to a different metabolite spectrum in pullets and those adult laying hens, differing in their feather pecking behavior, had a different pattern of bacterial metabolites in the intestine. We could identify gut bacteria being able to use keratin as substrate. Further studies are warranted, studying the relationship between the gut microbiome and behavior in hens. To what extend a targeted manipulation of the gut microbiome, e.g. by the use of probiotics, could help to solve the problem of feather pecking will be an intriguing question in the future.