Abstract
White chick hatchery disease is an emerging disease of broiler chicks with which the virus, chicken astrovirus, has been associated. Adult birds typically show no obvious clinical signs of infection, although some broiler breeder flocks have experienced slight egg drops. Substantial decreases in hatching are experienced over a two-week period, with an increase in mid-to-late embryo deaths, chicks too weak to hatch and pale, runted chicks with high mortality. Chicken astrovirus is an enteric virus, and strains are typically transmitted horizontally within flocks via the faecal–oral route; however, dead-in-shell embryos and weak, pale hatchlings indicate vertical transmission of the strains associated with white chick hatchery disease. Hatch levels are typically restored after two weeks when seroconversion of the hens to chicken astrovirus has occurred. Currently, there are no commercial vaccines available for the virus; therefore, the only means of protection is by good levels of biosecurity. This review aims to outline the current understanding regarding white chick hatchery disease in broiler chick flocks suffering from severe early mortality and increased embryo death in countries worldwide.
Highlights
Hatchery diseases occur when eggs become infected by pathogens, often leading to drops in the numbers of eggs laid, reduced hatches and/or embryonic defects such as dwarfing
Despite there being multiple varying strains of chicken astrovirus (CAstV) circulating in the farming environment, the distinctive strains that largely belong to the Biv subgroup have been identified as the probable causative agent for white chick hatchery disease
Despite the adult birds becoming infected with white chick hatchery disease-associated CAstV strains, there are no clinical signs in the adult birds; there is a much higher mortality rate in their offspring, with typical observations including an increase in mid-to-late embryo deaths and small, weak chicks with white plumage
Summary
Hatchery diseases occur when eggs become infected by pathogens, often leading to drops in the numbers of eggs laid, reduced hatches and/or embryonic defects such as dwarfing. White chick hatchery disease is a recently emerged disease affecting broiler chicks and embryos that has been reported in a number of regions worldwide This disease results in severe weakness in chicks that either prevents hatching, or chicks survive only briefly post-hatch with characteristic white down [4]. It had been problematic in North America for several decades [5], it was a letter to the Veterinary Record that first associated the disease with CAstV and described the first Finnish case, which appeared in a single broiler-breeder flock in 2006, with greater numbers of flocks infected in subsequent years [4]. Losses due to reduced hatchability can be very high, with Finnish veterinarians reporting an average hatchability drop of 29% across affected flocks, with one individual farm experiencing a loss of 68% over a two-week period [4]
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