Investigation regarding the occurrence of fowl adenovirus (FAdV) in dead-in-shell chicks and young broiler breeders in Sweden.

Abstract

This paper describes the investigation of the epidemiology of fowl adenoviruses (FAdVs) among fast-growing meat-type breeder parent chickens in Sweden, based on serology, PCR and partial genome sequencing of samples collected during rearing and egg production. Blood samples (n = 1910) from breeder flocks at 16 (79 flocks), 24 and 36 (52 flocks) weeks of age were analysed for FAdV antibodies. Ninety-four percent of the flocks had seroconverted at 16 weeks of age, and at 36 weeks of age all 52 flocks were seropositive. From 35 of these flocks, dead-in-shell chicks (DIS, n = 949) from eggs laid at 26-27 and 36-37 weeks of age were sampled, and pooled liver and caecal tonsils were analysed by PCR. Nucleic acid from FAdV was not detected. Negative PCR results were confirmed by testing tissues from 62 broiler breeders and 80 DIS from four additional seropositive flocks, collected at age 24-26 weeks. From six other breeder flocks, liver and caecal tonsils were sampled from one bird (when available) per day during rearing from 1-112 days of age. From 6 weeks of age, in 4/6 flocks, FAdV species A and/or D were detected by PCR and partial hexon gene sequencing. In conclusion, FAdVs were detected during rearing in breeder birds but not in DIS. This suggests that vertical transmission of FAdVs was prevented by immunity acquired early in life. However, it should be noted that high antibody titres in breeder birds does not necessarily confer protection against vertical transmission.RESEARCH HIGHLIGHTSThe majority of 16-week-old parent flocks were seropositive to FAdV.FAdV was not detected by PCR in dead-in-shell chicks from seroconverted flocks.FAdV-A and D were detected in broiler breeders during rearing from 6 weeks of age.Results suggest that vertical spread was prevented by immunity in breeder birds.