A matched cohort study investigating the risk of Mycobacterium bovis infection in the progeny of infected cows

The aim of this study was to quantify the risk of bovine tuberculosis in the progeny of cows confirmed as having bovine tuberculosis. Historical computerised records were used to undertake a retrospective cohort study. The exposed cohort was defined as the last calf of dams that were diagnosed as having bovine tuberculosis during 2002. The progeny were only retained for subsequent analysis if they were born in the 9. months preceding slaughter of the dam and if they lived for more than 15. months. The unexposed cohort comprised of animals born in the same herd within 1. month of the exposed cohort and was matched one-to-one. The resultant dataset contained 1156 matched cohorts. Forty-two animals from the exposed cohort and 35 from the unexposed cohort had bovine tuberculosis. The relative risk was estimated at 1.2 (95% confidence interval 0.8-1.79). It was concluded that progeny of tuberculous dams were not at a significantly increased risk of Mycobacterium bovis infection.