Microbiological Investigations of Bacteria Infecting Yolks of Broiler and Broiler Breeder Embryos and Newborn Chicks

Chicken embryo mortality has been attributed to bacterial infections resulting in a decline in hatchability, and significant losses in the broiler industry. The aim of this study was to investigate the vertical transmission of specific bacterial pathogens from breeder hens to subsequent broiler flocks. In our sampling of 360 commercial broiler eggs, we isolated Enterococcus gallinarum and Enterococcus faecalis, from yolks of 17-day incubated eggs. Enterococcus avium was recovered by culture enrichment from 1 of 31 unincubated yolks. From 297 eggs yolks from broiler breeders incubated for 17 days we isolated E. faecalis, Globicatella sanuinis, and E. gallinarum, in some cases in high numbers. We then performed microbiological sampling of day-of-hatch chicks for broilers from a commercial hatchery. Culture enrichment and sampling of intestine and residual yolk sac suggested only yolk sac was likely to yield bacterial growth, and could be sampled directly by swabs onto growth medium. The most common isolate from sampling 30 newly hatched broiler chicks was E. faecalis from 16 different chicks. However, E. coli was recovered as a mixed infection with E. faecalis in 3 of those 16. Residual yolk sacs were then swab-sampled from day-of-hatch broiler breeder chicks. E. faecalis was recovered from 7 out of 40 chicks. Thus, yolk infections by Enterococcus species should be of concern in the broiler industry, and could be contributing to reduced hatchability, early chick death, and transmission of bacteria from hens to subsequent flocks.