Feather bacterial load affects key avian life-history traits such as plumage condition, innate immunity, and reproductive success. Investigating the interplay between life-history traits and feather microbial load is critical for understanding mechanisms of host-microbiome interactions. We hypothesize that spatiotemporal variation associated with migration and molting, body size affecting colonizable body surface area, and preening intensity could shape feather bacterial load. Integrating 16S rDNA-qPCR and flow cytometry, we examined total and viable bacterial loads in the feathers of 316 individuals of 24 Palearctic passerine species. We found that viable bacterial load in feathers was lower in larger species and higher in residents compared to migrants. In contrast, total bacterial load was not explained by any of the life-history traits but varied considerably among species, sampling sites, and years. By pinpointing main drivers of bacterial loads on avian body surfaces, we identify key mechanisms shaping host-microbiome interactions and open alternative research directions.

• Keywords
• Evolutionary biology, Microbiology, Ornithology,
• Publication type
• Journal Article MeSH

Preen gland secretions spread on the feathers contain various chemical compounds dominated by fatty acids (FAs) and volatile organic compounds (VOCs). These chemicals may significantly affect plumage condition, microbial and ectoparasitic load on feathers, and chemical communication of birds. However, how chemical composition of preen secretions varies in commercially produced chickens with respect to their genotype, sex, and feeding regime remain largely unknown, as well as the welfare implications for farmed poultry. We found that while polyunsaturated fatty acids in chicken preen secretions differed significantly with genotype (P << 0.001), saturated fatty acids and monounsaturated fatty acids varied with genotype-dependent preen gland volume (P < 0.01). Chickens of meat-type fast-growing Ross 308 genotype had reduced preen gland volume and lower proportions of all FA categories in their preen secretions compared with dual-purpose slow-growing ISA Dual chickens. A total of 34 FAs and 77 VOCs with tens of unique FAs were detected in preen secretions of both genotypes. While differences in the relative proportion of 6 of the 10 most dominant VOCs in chicken preen gland secretions were related to genotype (P < 0.001), only 1 of the 10 most dominant VOCs showed a sex effect (P < 0.01), and only 2 of the 10 most dominant VOCs showed a genotype-dependent effect of feed restriction (P < 0.05). Feed restriction had no effect on the relative proportion of any of the FAs in chicken preen gland secretions. Moreover, we found that meat-type Ross 308 preen secretions were dominated by VOCs, which are proven attractants for poultry red mite and may also increase infestation with other ectoparasites and negatively influence overall odor-mediated intraspecific communication and welfare. This study shows that no feeding management, but long-term genetic selection in commercial breeding may be the main cause of the differences in the biochemistry and function of chicken preen secretions. This might have negative consequences for chemosignaling, antiparasitic, and antimicrobial potential of preen secretions and can lead to increased susceptibility to ectoparasites, plumage care disorders, and can affect the overall condition, welfare, and productivity of commercially bred chickens. Selection-induced preen gland impairments must therefore be considered and compensated by proper management of the chicken farm and increased care about animal well-being.

The preen gland is the largest sebaceous gland in birds, which produces a secretion that is spread on the feathers during comfort behavior. The secretion of the preen gland contains various chemical compounds that are responsible for mechanical, antimicrobial, and antiparasitic protection of the plumage and probably also for chemical communication between birds. However, there are only a limited number of studies on the composition and function of preen secretions in wild birds and only limited evidence in poultry. In this study, we compared the chemical composition of preen secretions in fast-growing meat-type and slow-growing dual-purpose chickens and evaluated the effect of sex, body condition, and feeding regime on preen secretion composition. Fast-growing meat-type chickens had smaller preen glands and lower proportions of all analyzed compounds in preen secretions compared to slow-growing dual-purpose chickens. In addition, compounds that are proven attractants for a poultry-threatening ectoparasite, poultry red mite, were predominant in the secretions of meat-type chickens. This study is the first to show that genetically distinct breeds of chickens can differ significantly in the biochemistry of preen secretions, which can influence susceptibility to ectoparasites, plumage care disorders, and can affect the overall condition, well-being, and productivity of commercially raised chickens.

• Keywords
• antimicrobials, chemosignaling, ectoparasites, feather condition, uropygial gland, welfare,
• MeSH
• Anti-Infective Agents * MeSH
• Poultry MeSH
• Genotype MeSH
• Chickens * genetics   MeSH
• Fatty Acids MeSH
• Sebaceous Glands MeSH
• Grooming MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anti-Infective Agents * MeSH
• Fatty Acids MeSH