Microbiological Investigations of Bacteria Infecting Yolks of Broiler and Broiler Breeder Embryos and Hatchlings

Enterococcus cecorum has been identified as causing early sepsis in commercial broilers. We hypothesized that vertical transmission may contribute to the spread of the pathogen. Sampling of 360 commercial broiler eggs from a previously infected flock detected Enterococcus gallinarum and Enterococcus faecalis in yolks of 18-day incubated eggs. Enterococcus avium was recovered by enrichment from 1 of 31 unincubated yolks. Direct sampling without enrichment of 297 egg yolks from a previously infected broiler breeder flock detected E. faecalis, Escherichia coli, Globicatella sanguinis, and E. gallinarum, often in high numbers, or in coinfections. Microbiological sampling of day-of-hatch chicks suggested only the yolk sac was likely to yield bacterial growth, and that yolks could be sampled directly using swabs streaked onto growth medium. The most common isolate from sampling 30 day-of-hatch broiler chicks was E. faecalis from 16 different chicks. Further, E. coli was recovered as a mixed infection with E. faecalis in 3 of those 16 residual yolk sacs. From swab-sampling of residual yolk sacs from 40 day-of-hatch broiler breeder chicks, E. faecalis was recovered from 7 chicks. Thus, yolk infections by Enterococcus species were the primary isolates cultured from commercial broilers and broiler breeders in Arkansas. Identification of these species at high numbers in yolks is likely contributing to reduced hatchability, early chick death, and transmission of bacteria to subsequent flocks. Therefore, the broiler industry needs to pursue methods to identify infected laying hens and management strategies to mitigate vertical transmission. Importance: We were unable to identify E. cecorum being spread from flock to flock via vertical transmission. We did identify specific bacterial species infecting and reproducing within the yolks of developing embryos and day-old chicks of commercial, meat-type chickens. These particular species were detected at low and high levels, indicating growth within the yolk. The implication is that these species colonized the yolk within the hen’s reproductive tract and were vertically transmitted to the chicks and subsequent flocks. Some infections represent only a single species, while others involve two species that may represent cooperative infections. With the removal of the use of antibiotic growth promoters during early development, these species may be reducing chicken reproduction through embryo death or early chick mortality.