Published gut microbiota comparisons show similarity between hens and their progeny, implying the possible vertical transmission of commensal bacteria from one generation to the next through the egg. However, it has also been shown that exposure to adult hens greatly affects chick microbiota composition and function, implying vertical transmission through the egg is limited and direct contact with an adult is needed to facilitate transmission. Characterizing vertical transmission through the egg is important to the development of methods that enhance the transmission of commensals while inhibiting pathogen transmission. Furthermore, identifying bacterial phylogenetic groups which do not transmit effectively through the egg is important, as this might affect the maturation of microbiota composition and function.
How we investigated or researched the problem
Thus, we collected fertilized eggs from ten broiler breeders and grew their chicks for 14 days. We collected fecal samples from the hens during egg collection week and from the chicks at ages 2, 7, and 14 days. We then performed 16S rDNA sequencing and compared microbial communities, at the amplicon sequence variant (ASV) level. We performed two additional growth cycles with the same hens.
We found that most ASVs identified in the hens did not appear at all in the chicks up to day 14 of growth. Furthermore, most of the these that did appear were identified in just a few chicks. Only three ASVs were found to be efficient colonizers of newly hatched chicks, appearing in most chicks already on day 2 of life. These same three ASVs were the most efficient colonizers in each of the three growth cycles. Analysis of efficient and moderate colonizers showed Lactobacillaceae and Lachnospiraceae to be highly represented. Analysis of ASVs found in the chicks but not in the hens, representing possible opportunistic bacteria, showed none to be efficient colonizers of newly hatched chicks.
Implications / Conclusions
Our results show vertical transmission of commensal gut bacteria from hen to chicks through the egg is very limited if it occurs at all. While we only measured colonization till day 14, this already represents about a third of the life span of broilers. Thus, it is clear that the gut microbiota of chicks is underdeveloped. Further research is required to determine the impact of the lack of transmission of these gut commensals on commercial broilers, and if artificial exposure can positively impact broilers. Last, we identified a handful of bacterial strains common with the hens that did colonize chicks efficiently. Further work is required in order to determine if these strains transmit through the egg or through the environment.
Presented at the 7th International Conference on Poultry Intestinal Health, Cartagena, Colombia, 2022. For information on the next edition, click here.