Vertical transmission of gut bacteria in commercial chickens is limited

The existence of vertical transmission in chickens under commercial settings, where chicks are raised separated from adults, is unclear. To answer this question, the fecal microbiota of chicks hatched and grown separately was compared with their mothers’ microbiota. Most amplicon sequence variants (ASVs) identified in hens did not appear at all in chicks up to two weeks of age, and those that did appear had a low incidence among the chicks. Nevertheless, a few ASVs that were common with the hens were highly prevalent among the chicks, implying they were efficiently transmitted to chicks. These ASVs were culturable from the reproductive tract of hens and eggshells. Furthermore, interventions attempting to disrupt transmission resulted in a reduction of prevalence in chicks. To conclude, vertical transmission in commercial poultry grown separately from adults likely exists but is not efficient, possibly resulting in impairment of microbiota function. This implies that artificial exposure to adult bacterial strains might improve microbiota functioning.