Genetic analyses of pathogen-specific mastitis.

The aims of this study were to investigate the presence of genetic variation for susceptibility to pathogen-specific mastitis and to examine whether haplotypes of an identified quantitative trait locus with effect on unspecific mastitis resistance had different effects on specific mastitis pathogens. Bacteriological data on mastitis pathogens were obtained from the diagnostic laboratory at the Swedish National Veterinary Institute. The data were mainly from subclinical cases of mastitis but also clinical cases were included. Variance components were estimated for incidence of the six most frequent pathogens using Markov Chain Monte Carlo methodology via Gibbs sampling. Genetic variation for susceptibility to pathogen-specific mastitis was higher compared to estimates of general resistance to clinical mastitis in most other studies. However, because of the non-random nature of data collection, comparisons to other studies should be made by caution. The effect of haplotype on the risk of being infected by a given mastitis pathogen, relative to other pathogens, was studied using an allele substitution model. Although there were no significant haplotype substitution effects on the resistance to any of the six mastitis pathogens, there was a significant difference between the effects of two of the haplotypes regarding the risk of acquiring a Streptococcus dysgalactiae infection.