Yolk sac, body dimensions and hatchling quality of ducklings, chicks and poults

Abstract

1.	One-day-old chicks of Pekin duck, turkey, layer fowl and broiler fowl were examined for bacteria in the yolk sac and yolk fluid.
2.	Whole hatchling, yolk-free hatchling and yolk sac weights were recorded for all species along with crown–rump length and beak-tip to toe-tip length.
3.	Bacteriology revealed positive results for the whole yolk sacs of 43 to 64% of the birds in the sample of ducklings, poults and layer chicks. Broiler chicks had a 6·6% incidence of bacteria isolated from the whole yolk sac. By contrast, there were very few positive results from swabs of yolk fluid for any of the bird types.
4.	The presence of bacteria in the yolk sac of hatchlings suggests that there is colonisation, rather than infection, of the yolk sac membrane during the hatching period or the first few hours post-hatching. Isolation of bacteria from the yolk sacs of young chicks might no longer be considered as solely indicative of yolk sac infection but further research is required to confirm this result.
5.	Contrary to what is being suggested in commercial practice relationships between linear dimensions and hatchling weight suggest that measurement of chick length is at best a very crude measure of chick quality.

Acknowledgements

This research was funded by Cherry Valley Farms Ltd and I am indebted to Mr Richard Bird and Mr David Martin for permission to publish it. Many thanks to Hayley Johnson for liasing with the laboratory over the microbial cultures. I thank Barry Hughes for his constructive editing of the manuscript. Many thanks are due to the managers of the duck, turkey, layer and broiler hatcheries that were so forthcoming in supplying the chicks sampled in this study.