Effects of experimental infection of fowl with EDS'76 virus, infectious bronchitis virus and/or fowl adenovirus on laying performance

Abstract

SUMMARY Following BCI4 (EDS'76) virus infection of brown layer hens at 33 weeks of age, production of normally shelled eggs dropped from 87 per cent to 49 per cent within 3 weeks. The production of soft shelled and shell-less eggs attained a maximum of 33 per cent 3 weeks after infection (p.i.). Shell quality recovered completely within 5 weeks p.i. Egg production problems in White Leghorns infected with BCI4 virus were less severe and of shorter duration than in brown layers. Both in brown layers and in White Leghorns total egg production, mean weight of normally shelled eggs, and internal egg quality were not affectedfollowing BCI 4 virus infection at 33 and 28 weeks of age, respectively. Besides shell abnormalities no clinical disease symptoms were observed. Vaccination with a commercial EDS'76 vaccine (Nobivac EDS'760) at 17 weeks of age had no adverse effects on laying performance and provoked adequate immunity against challenge at 33 weeks of age. The same observations were made following BCI4 virus infection at 17 weeks of age. After infectious bronchitis virus (IBV) (H52 virus) infection of laying fowl the percentage of eggs with shell aberrations (rough, misshapen and/ or soft shells) increased to a maximum of 8 per cent, total egg prodtiction was depressed, mean egg weight was reduced I to 2 grams, and up to 10Per cent of normally shelled eggs showed watery, not ropy thin albumen. This abnormally thin albumen was observed in a considerably higher proportion of eggs with shell defects than in normallr shelled eggs. No turbidity of the thick albumen was observed and no symptoms of respiratory disease were noticed. The severity and duration of adverse effects of 1BV infection on laying performance depend very much on the stage of production in which the infection occurs. Following 1BV infection at the onset of production a much severer drop in total production and in production of normally shelled eggs, a greater increase in the number of abnormally shelled eggs, and more lasting adverse effects on egg weight and internal egg quality were observed, in comparison with infection after peak production. Compared with single infections, a combined BC14 virus and 1BV infection of brown layers at 33 weeks of age resulted in greatly potentiated adverse effects on total egg production, number ofeggs with aberrant internal quality, and duration.of production problems.Following a combined BC14 virus and 1BV infection, in a great proportion of eggs with shell defects and watery thin albumen, turbidity of the thick albumen was observed also, probably due to combined effects on the uterus of both 1BV and BC14 virus. BC14 virus infection did not reinforce the adverse influence of 1BV infection on egg weight. The same observations as described for the combined BCI4 virus and IBV infection were made following BCI4 virus infection of fowl previously infected with 1BV.It is concluded that changes of internal egg quality in field cases of EDS'76 are most likely due to subclinical IBV infections. After infection of brown laye...

Coronaviridae: Infectious Bronchitis Virus

“…About 6 to 8 weeks may elapse before production returns to the pre-infection level, but in some cases, this is never attained. The severity of the production declines may vary with the period of lay (van Eck 1983). In addition to production declines, the number of eggs unacceptable for setting is increased, hatchability is reduced, and soft-shelled, misshapen, and rough-shelled eggs are produced (Crinion 1972).…”