Studies on a depressed egg production syndrome in Northern Ireland.

A syndrome causing depressed egg production is described. It is characterised either by a failure to attain predicted production targets or by a fall in egg numbers. The depression in production can reach 30% and it may or may not return to normal. For a short period the eggs produced are smaller, lose colour, have poor egg shell strength and many soft shelled eggs are laid. The birds remain apparently healthy and there is a marked age incidence, with most flocks starting this depression in egg production at 29-31 weeks of age. This syndrome has been recently recorded in the Netherlands, but has not been seen before in Northern Ireland. Viruses which agglutinated fowl erythrocytes to very high titres were isolated in chick embryo liver cells from six affected flocks. Three of these isolates were from the oviduct, two from the upper respiratory tract and one from the faeces. These agents are similar to adenoviruses, but were not neutralised by antisera to 11 prototype fowl adenoviruses. In addition, 17 adenoviruses were also isolated from the flocks showing the syndrome described. These isolates fell into five serological types, in addition to nine which could not be typed using antisera to 11 prototype adenoviruses. Investigations of flocks with falls in egg production not conforming to this syndrome yielded five isolates. Six adenoviruses were also isolated from birds with diarrhoea.