TABLE 1: Description of the four disease classes associated with the development of digital dermatitis (Dopfer 1994

Research on physical or psychological stress, in order to monitor objective parameters for animal welfare, is usually performed during experimental stress induction. To avoid treatment of animals with physical or physiological stress, addition of the stress-related hormone corticosterone to the drinking water, may serve as a practical alternative to reproducibly investigate hormone-related stress in broiler chickens. Rapid uptake of the hormone and distribution in the bloodstream were affirmed by elevated plasma corticosterone concentrations immediately after start of the treatment. The effect of hormone administration was evaluated by examination of corticosterone-sensitive organs. Comparable to the observations during physiological stress, we found in our model that uptake of endogenous corticosterone reduced body and spleen growth, increased heterophil counts, and decreased formation of antibodies against sheep red blood cells. Furthermore, corticosterone decreased adrenal gland responsiveness, measured by corticosterone production, after a challenge with adrenocorticotropic hormone. The simple performance, and the close relation between circulating corticosterone levels and heterophil counts, makes this an easy and quick method that is sensitive to increased levels of circulating corticosterone from base levels. The changed responsiveness of the adrenal glands to adrenocorticotropic hormone after increased circulating corticosterone levels may be an indication of the coping strategies during stress. Therefore, this test may be a promising tool in the research of adaptation to stress by broiler chickens.

The culturability of 10 strains of Campylobacter jejuni and Campylobacter coli was studied after the bacteria were exposed to acid conditions for various periods of time. Campylobacter cells could not survive 2 h under acid conditions (formic acid at pH 4). The 10 Campylobacter strains could not be recovered, even when enrichment media were used. Viable cells, however, could be detected by a double-staining (5-cyano-2,3-ditolyl tetrazolium chloride [CTC]-4,6-diamidino-2-phenylindole [DAPI]) technique, demonstrating that the treated bacteria changed into a viable but nonculturable (VBNC) form; the number of VBNC forms decreased over time. Moreover, some VBNC forms of Campylobacter could be successfully resuscitated in specific-free-pathogen fertilized eggs via two routes, amniotic and yolk sac injecting.

Many recent outbreaks of infectious bursal disease in commercial chicken flocks worldwide are due to the spread of very virulent strains of infectious bursal disease virus (vvIBDV). The molecular determinants for the enhanced virulence of vvIBDV compared to classical IBDV are unknown. The lack of a reverse genetics system to rescue vvIBDV from its cloned cDNA hampers the identification and study of these determinants. In this report we describe, for the first time, the rescue of vvIBDV from its cloned cDNA. Two plasmids containing a T7 promoter and either the full-length A-or B-segment cDNA of vvIBDV (D6948) were cotransfected into QM5 cells expressing T7 polymerase. The presence of vvIBDV could be detected after passage of the transfection supernatant in either primary bursa cells (in vitro) or embryonated eggs (in vivo), but not QM5 cells. Rescued vvIBDV (rD6948) appeared to have the same virulence as the parental isolate, D6948. Segment-reassorted IBDV, in which one of the two genomic segments originated from cDNA of classical attenuated IBDV CEF94 and the other from D6948, could also be rescued by using this system. Segment-reassorted virus containing the A segment of the classical attenuated isolate (CEF94) and the B segment of the very virulent isolate (D6948) is not released until 15 h after an in vitro infection. This indicates a slightly retarded replication, as the first release of CEF94 is already found at 10 h after infection. Next to segment reassortants, we generated and analyzed mosaic IBDVs (mIBDVs). In these mIBDVs we replaced the region of CEF94 encoding one of the viral proteins (pVP2, VP3, or VP4) by the corresponding region of D6948. Analysis of these mIBDV isolates showed that tropism for non-B-lymphoid cells was exclusively determined by the viral capsid protein VP2. However, the very virulent phenotype was not solely determined by this protein, since mosaic virus containing VP2 of vvIBDV induced neither morbidity nor mortality in young chickens.

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