Genetic and phenotypic aspects of infection with Mycobacterium avium ssp. paratuberculosis in German Holstein cows
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Mycobacterium avium ssp. paratuberculosis (MAP) is the causative agent for the global occurrence of paratuberculosis (Johne´s disease) in ruminants. Infection with MAP leads to chronic enteritis and is responsible for economic losses, especially for dairy farmers. Because of cost and time efficiency the majority if studies about MAP infection deal with ELISA test results for phenotyping. The present study demonstrates with a dataset of 9 367 fecal culture tested German Holstein cows that the MAP status of the animals, the farm and the lactation number, as well as the interaction between MAP status and farm significantly affect the milk parameters, especially milk yield in kilograms. Also the interaction between lactation number and MAP status is significantly associated with milk kg per day of life. Although, if only a part of the real losses could be considered, the presented results of MAP infection to production traits underline the economic importance to control and eradicate the disease.So far, there is no therapy or vaccination against MAP, but there are suggestions that susceptibility to MAP infection has a genetic component. To verify the hypothesis also for fecal culture tested animals, a large dataset of 11 285 fecal culture tested German Holstein cows were used to estimate heritability for MAP infection. With results between 0.157 and 0.228 it could be demonstrated that the fecal culture test method is more suitable for further studies than ELISA test results. Furthermore, the estimated heritabilities are comparable with other traits which are already included successfully in breeding programs.Because of the genetic background of the disease, numerous studies deal with the analysis of possible candidate genes and their association with MAP infection as well as with genome-wide association (GWA) studies to identify genetic region of interests with MAP infection. Amongst others the nucleotide-binding oligomerization domain containing 2 (NOD2, formerly CARD15) was described as a candidate gene for susceptibility with MAP infection in cattle. In the present study eleven SNPs in the NOD2 gene could be identified, and finally, four SNPs were included in a case-control study using 324 German Holstein cows tested for paratuberculosis using fecal culture and ELISA. Thereby the SNP (GenBank) AY518738S04:g.521G>A in exon 4 showed a significant association (P = 0.0056) between the fecal culture status of the animals and NOD2 allele variants. Furthermore a GWA study was performed with the Illumina Bovine SNP50BeadChip using a case-control assay of 305 cows tested for MAP by fecal culture with an additional four different commercial ELISA-tests. No so far reported association for MAP infection could be confirmed. However, new regions of interest and potential candidate genes could be found. These results lead to the conclussion, that different test methods for MAP infection result in diverse identified gene loci, and therefore in different candidate genes associated with MAP. Furthermore it seems to be once more, that paratuberculosis is not affected by just one gene. The results of the present study are reflecting the problem of the diagnostic of MAP infection. The different test methods and the different grouping of phenotyping leads to different results of the studies. Therefore, further improvement of diagnostic for MAP infection is essential to get a correct and consistent phenotype for further studies concerning MAP infection. Beside which, the phenotyping of the large number of tested animals, at best with whole pedigree information, is a limitation factor for genetic studies. Both improvement of phenotyping and the increasing number of animals are basic factors for further genetic studies of MAP infection.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Giessen : VVB Laufersweiler