Assessing familial aggregation of paratuberculosis in beef cattle of unknown pedigree.

The objective of this study was to assess genetic similarity of beef cattle using microsatellite markers and to use this information to describe familial aggregation of paratuberculosis test results in Texas beef cattle. Paratuberculosis testing was performed on 2622 adult beef cattle using two commercially available serum ELISAs and radiometric fecal culture. Pedigree records were collected for registered purebred herds and herds with sufficiently detailed production records to identify parent-offspring pairs. Cases were defined as cattle with at least one positive paratuberculosis test result. Three controls were matched by herd of residence for each case. All parent-offspring pairs, cases, and controls were genotyped for 12 microsatellites. Bayesian analysis of allele frequency data was used to describe population substructure and assign individual cattle into groups of genetically similar cattle. The proportion of known parent-offspring pairs assigned to the same cluster was used to assess the validity of the approach to identify familial structure. Conditional logistic regression was used to describe the association between cluster assignment and paratuberculosis test-status matched by herd. Nine clusters of genetically similar individuals were identified and were supported by the proportion of parent-offspring pairs assigned to the same clusters. Increased odds of having at least one positive paratuberculosis test result were identified for two clusters compared to the cluster with the lowest proportion of positive paratuberculosis test results after conditioning on herd. The results of this study demonstrate that population substructure can be used to describe familial aggregation of paratuberculosis test results in beef cattle of unknown pedigree.