The experimental inoculation of 38-week-old turkey hens with a pool of field isolates of turkey rhinotracheitis virus (TRTV) induced a marked respiratory infection and a substantial drop in egg production. Administration of a live-attenuated TRT vaccine at 1 week of age did not protect the layers against respiratory infection, but provided good protection against the effects of challenge on laying performance. However, a combination of live priming followed by injection of inactivated vaccine provided excellent protection against both respiratory infection and drops in egg production.

Administration of a virulent strain of avian pneumovirus (APV) to specific pathogen free laying hens by the oculonasal route failed to induce a drop in egg production or any adverse effects on eggshell quality. However, intravenous (i.v.) inoculation of the same strain caused a substantial drop in egg production and a high incidence of soft and thin-shelled eggs. Some respiratory signs were also observed and the hens appeared sick, with diarrhoea being observed in approximately one-half of the hens between 4 and 11 days post-inoculation (p.i.). APV antigen was detected in the oviduct epithelium up to 9 days p.i. This challenge model was then used to investigate the efficacy of live attenuated turkey rhinotracheitis (TRT) vaccine administered alone at 1 day old, or an inactivated TRT vaccine (at 16 weeks), or a combined programme using both vaccines, in protecting against this challenge. Neither the live nor the inactivated vaccine alone protected against clinical signs (respiratory infection or diarrhoea). However, the inactivated, but not the live, vaccine did protect against the effect of the i.v. challenge on laying performance. In contrast, the combined vaccination programme protected completely against both clinical signs and poor egg-laying performance. This protection lasted until at least 60 weeks of age. On the basis of the results with this experimental model, it is concluded that the use of live priming followed by administration of inactivated TRT vaccine is necessary to provide complete protection of laying chickens against APV challenge.

No abstract

The administration of two commercial Newcastle disease (ND) vaccines to chickens by aerosol was studied. The size distribution of non-evaporating droplets, produced by different aerosol generators, was measured. Using one of the generators - the Atomist - the size distribution of particles evaporating to equilibrium was determined. The sedimentation of the dry particles was judged by repeating the measurement after 10 and 30 min. This was done with distilled water, tap water, saline, and 1% and 2% solutions of Casitone, with and without vaccine. The stability of the vaccine virus at 20 degrees C in an aerosol of distilled water was minimal at high relative humidities. Measurement of viral stability in aerosols of different diluents produced with the Atomist in small pens showed an initial loss of infectivity of between 1 and 3 log(10) median embryo infectious doses (EID50). Further loss of infectivity was between 0.2 and 3.4 log(10) EID50/ hour. Distilled water was the optimal diluent for these commercial ND vaccines.

As part of a larger experiment to compare the pathogenic effects of different strains of Marek's disease virus, a counting procedure for tissue components in histological sections is presented which may quantify the relative volumes occupied by the components. The method is demonstrated on spleens taken from 8-weeks-old chickens, treated at one-day-old with a cell-associated pathogenic strain of Marek's disease virus (MDV), a cell-associated vaccine strain, or a MDV-free cell suspension.