Research Note: Correlation between the reproductive tract microbiota and speckled eggs in laying hens.

The microbiomes of the reproductive tract play a crucial role in the egg production and quality and reproductive health of laying hens. Speckled eggs are characterized by shells with brown spots of varying sizes and commonly produced by brown-shelled laying hens. Speckles reduce the economic value of eggs. However, the relationship between oviduct and cloacal microbiomes and the presence of speckled eggs in laying hens remains unclear. In this study, we collected samples from the reproductive tracts (uterus, vagina, and cloaca) of hens laying speckled eggs and those laying normal eggs and compared their microbial structures and relative abundances through 16S rRNA sequencing. We found that the microbial community structure in the reproductive tracts of the hens laying speckled eggs was similar to that in the reproductive tracts of the hens laying normal eggs; however, the relative abundances of Clostridium in the uterus and Turicibacter and Gallibacterium in the vagina of the hens from the speckled group (7.27%, 6.83% and 0.10%, respectively) were significantly higher than those in the normal group (2.00%, 0% and 0%, respectively [P < 0.05]). Additionally, 8, 24, and 11 bacterial taxa in the uterus, vagina, and cloaca were different between the groups of hens laying speckled and normal eggs. At the same time, Clostridium in the uterus may be associated with eggshell speckles. However, further investigations are necessary to understand the functions of these microbiota in the reproductive tracts of laying hens. This study provides novel insights into methods for reducing the occurrence of speckled eggs in laying hens.