Mycoplasma gallisepticum vaccination-challenge: an egg-production model.

Specific-pathogen-free layer hens in maximum lay were exposed by aerosol to a broth culture of Mycoplasma gallisepticum R' strain. Egg-production loss of greater than 50% was evident 7-14 days following challenge of unvaccinated chickens, with a gradual recovery during the next several days. Various vaccine preparations were tested to determine the effect in the model. All vaccinated chickens exhibited significantly (P < or = 0.05) lower egg-production loss than the unvaccinated controls. The model provides a method for testing treatment effects on egg-production losses resulting from controlled exposure to M. gallisepticum and may be useful in simulating field exposure.

Influence of coccidiosis on growth rate and feed conversion in broilers after experimental infections with Eimeria acervulina and Eimeria maxima.

Under experimental conditions, the effects of subclinical Eimeria (E.) acervulina and E. maxima infections on growth and feed conversion in broilers of different ages were analysed. It was concluded that infection with E. acervulina and E. maxima led to a process which was independent of the age at which the birds were infected. The infection adversely affected growth and feed conversion for 2 to 3 weeks, followed by a recovery period of 2 to 3 weeks when compensatory growth took place. From this study it may be concluded that subclinical coccidiosis in the first weeks of life and in the last week of life of broilers does not lead to appreciable damage on growth and feed conversion. Since coccidiosis cannot be avoided in practice, systems in which broilers contact subclinical coccidiosis either in the first weeks of life or in the last week of life should be aimed for. It is suggested that in a coccidiostat programme an efficient anticoccidiosis agent is particularly desirable in the 3rd and 2nd week before slaughter. Examinations performed one week or less before slaughter can hardly be justified, on the grounds that there is a risk of a negative effect on growth an feed conversion due to subclinical coccidiosis.

[Analysis of losses due to subclinical small intestinal coccidiosis caused by Eimeria acervulina and Eimeria maxima under field conditions]. / Een analyse van de schade van subklinische dunne darm coccidiosis veroorzaakt door Eimeria acervulina en Eimeria maxima onder praktijkomstandigheden.

Subclinical coccidiosis of broiler chickens caused by Eimeria (E.) acervulina and E. maxima results in a negative effect on feed conversion and retardation of growth. In the present report investigations in 80 broiler flocks are described in which the relationship between age of infection and economic effects were analysed under field conditions. Under these conditions, infections with E. acervulina and E. maxima were found to have a negative effect on growth and feed conversion, that this negative effect persists and accumulates for approximately three weeks following infection, and is subsequently completely or partly compensated for by increased growth rates. In the present study it was established that the losses due to subclinical coccidiosis of the small intestine in the 80 flocks investigated amounted to 6.4 cents per chicken under conditions occurring in the Netherlands. Ionophorous coccidiostats did not prevent infection with E. acervulina and E. maxima but did prevent infections with E. brunetti, E. necatrix and E. tenella.

The use in practice of inactivated oil emulsion vaccine against infectious bursal disease in broiler breeders and its influence on the progeny: a comparative field trial.

Field trials were conducted to establish the effect of the use of an inactivated oil emulsion vaccine against Infectious Bursal Disease (IBD OEV) in broiler breeder hens, and its effects on their progeny. The performance of 18 broiler flocks, which were the progeny of the IBD OEV vaccinated breeder hens, but which were not vaccinated with a live vaccine against IBD, was equal to that of broiler flocks which were vaccinated with a live IBD vaccine and originated from parent stock that had been vaccinated only against IBD with a live vaccine. In none of the 18 flocks, progeny of IBD OEV vaccinated parents, was IBD diagnosed. In a second stage, 15 broiler flocks were included in the trial: these were derived partly from IBD OEV vaccinated parents, and partly from parents that received only live IBD vaccine at 8-10 days of age. No cases of IBD occurred and all flocks were positive for IBD precipitins at slaughter age. Vaccination with a live vaccine against IBD at the age of 8-10 days had no influence on NCD antibody development after a NCD vaccination at 7 days. No immunosuppressive effect from this type of live live IBD vaccine could be determined under field conditions.

A study of Newcastle disease vaccine virus in sprays and aerosols.

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.

Quantitative pathogenicity of Marek's disease virus and vaccine virus strains in chickens: macroscopical aspects.

Two virulent strains (JM and K) and one vaccine strain (CVI 988) of Marek's disease virus (MDV), together with two vaccine strains of the herpesvirus of turkeys (HVT) (FC 126 and PB-THV 1), all in the cell-associated state, were administered intramuscularly at 3.7 log TCID50 per dose to day-old SPF White Leghorn chickens. A control group of chicks received uninfected cells. The pathological parameters studied were onset and duration of clinical symptoms, mortality, bird weight and macroscopical lesions of peripheral nerves and visceral organs. Data were obtained from females autopsied at the age of 3, 8 and 20 weeks, and from chickens which died. Virological and serological data were procured mainly from males taken at various ages. The results indicate a clear distinction between virulent and vaccine strains. MD vaccines had no significant influence on bird weight and caused no mortality or macroscopical lesions, whereas the virulent MDV strains produced all these effects. Macroscopical lesions caused by the virulent MDV strains were seen predominantly in nerves (in about 50% of birds succumbing to MD) and gonads (in 0% to 80% of such birds depending on sex and on strain of MDV). Differences between the two virulent strains could be demonstrated. Strain JM induced earlier incidence and shorter duration of clinical disease. With strain JM death occurred earlier in females than in males. Strain K caused significantly more macroscopical lesions in gonads, heart and liver. Under the conditions of the experiment, detection of macroscopical lesions after inoculation with a virulent MDV strain was possible 3 weeks after inoculation.

Absence of Marek's disease virus antigen in the feather follicle epithelium of vaccinated chicks demonstrated by immunofluorescence.

In chickens vaccinated with MDV strain CVI 988, HVT strain FC 126 or PB-THV 1, no MDV-specific antigens could be demonstrated in the feather follicle epithelium by immunofluorescence (IF). In chickens given virulent MDV strains, the epithelium of the feather follicle was positive in IF. In an experiment where chickens were vaccinated with strain CVI 988, positive IF was observed in the lung, bursa and pancreas, but not in the feather follicle epithelium, kidney, cloaca, or caecal tonsils. Absence of IF antigen in the skin may be indicative of avirulence of the strain of MDV.

Comparison of live Newcastle disease vaccines in a simple vaccination and challenge experiment.

Groups of day-old chicks with haemagglutination inhibiting antibodies (HIA) were exposed by the spray method to equal doses of three different live Newcastle disease (ND) commercial vaccines and allantoic preparations of them. After three weeks the HIA response was measured and the chicks were challenged with a pathogenic strain of Newcastle disease virus (NDV). The degree of protection of each bird was compared with its HIA response. The commercial vaccines all provided good protection at identical levels, but significant differences were detected between the allantoic fluid preparations. Two of the commercial vaccines produced significantly better protection than the allantoic fluid preparations. In addition to the protection conferred by HIA antibody, other mechanisms of protection apparently played a part.

Histo-morphometric analysis applied to spleens of Marek's disease virus inoculated chickens.

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.