Chickens from replicated lines divergently selected for multitrait immunocompetence were tested for their antibody responses to sheep red blood cells and Brucella abortus antigen. All birds were injected with sheep red blood cells and B. abortus antigens at 4 and 9 wk of age, and blood samples were taken 6, 8, and 10 d postimmunization. Antibody titers were determined by using agglutination assays. For sheep red blood cell responses, the most marked difference was between the high and low lines postsecondary immunization. The high line titer was still rising at 10 d, whereas the low line had reached its peak at 8 d and was decreasing. This may be a result of the selection process in which the high line is selected for a high, persistent response to two T cell-dependent antigens at 3 wk postimmunization. For B. abortus responses, the only differences were between high and low lines postsecondary immunization. The high lines were always higher than the low lines, with differences getting smaller as time postimmunization increased. In summary, selection for multitrait immunocompetence resulted in changes in antibody response to unrelated antigens.
The relationship between antibody response to Salmonella enteritidis vaccine and internal organ burden of S. enteritidis is not fully understood. The genetic relationship, therefore, between postchallenge S. enteritidis burden and antibody response to S. enteritidis vaccine was determined in broiler breeder chicks. Sibling chicks from a broiler breeder male line were either inoculated with a pathogenic S. enteritidis or vaccinated with a commercial S. enteritidis vaccine. Spleen, liver, cecal wall, and cecal content samples from S. enteritidis-challenged chicks (n = 120) were cultured for enumeration of bacteria. Unchallenged chicks (n = 314) were vaccinated at 11 days of age, and serum samples were taken at 10 days postvaccination. Antibody response to vaccination and number of S. enteritidis in cecal content cultures were negatively correlated (-0.772), demonstrating that genetic potential for greater antibody response to S. enteritidis vaccine is associated with lesser S. enteritidis bacterial burden in cecal content of broiler breeder chicks. The findings suggest that genetic selection for vaccine antibody responsiveness can lower bacterial burden in the gut lumenal content and, thus, potentially reduce contamination of poultry products at processing.
The objective of this study was to investigate frequencies of major histocompatibility complex (MHC) class II restriction fragments in two groups of White Leghorn strains. Each group consisted of an unselected control, a strain selected for egg production traits, and a strain selected for egg production traits and Marek's disease (MD) resistance. PvuII-digested genomic DNA was hybridized with a chicken genomic MHC class II probe. The MHC class II DNA fragment frequencies in the selected strains differed from those in the related unselected control and in the strain selected using the same criteria from a different base population. Based on the sizes of the breeding populations, particularly those in the control strain and in the strain selected for egg production, it was considered unlikely that the observed changes of the MHC class II fragment frequencies were due to random genetic drift. The data suggested that some MHC class II bands are associated with production traits or with MD resistance, and that these associations tend to be unique to each genetic background. Hence, MHC class II genes are likely candidates for the investigation of quantitative trait loci in egg production and disease resistance traits such as those for which the studied strains were selected.
Since first emerging in the North American canine population in 2004, canine influenza virus (CIV) subtype H3N8 has shown horizontal transmission among dogs, with a high level of adaptation to this species. The severity of disease is variable, and coinfection by other respiratory pathogens is an important factor in the degree of morbidity and mortality. The first influenza vaccine for dogs, an inactivated vaccine containing CIV subtype H3N8, was conditionally approved by the U.S. Department of Agriculture (USDA) for licensure in May 2009 and fully licensed in June 2010. This study evaluates the efficacy of this vaccine to reduce the severity of illness in dogs cochallenged with virulent CIV andStreptococcus equisubsp.zooepidemicus.
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