| Summary: | The objective of this observational study was to quantify the association between Mycobacterium avium subspecies paratuberculosis (MAP) antibody status and risk of insemination and subsequent conception, in UK dairy cattle. Longitudinal milk recording, fertility and MAP antibody enzyme-linked immunosorbent assay (ELISA) milk test data were collated retrospectively from 121,762 lactations in 78 herds. Datasets were structured into appropriate units to suit outcomes and enable temporal association between current and future MAP status, and fertility measures. Current MAP status was categorised according to most recent status within 180 days, with time-related future MAP status assigned based on MAP antibody ELISA milk test data for each cow. Multilevel multivariable logistic regression models were used to evaluate associations between MAP status and 21-day pregnancy and submission rate and conception risk. Posterior predictions and cross-validation techniques were used to assess model fit and check model building assumptions.
A negative association was found between risk of insemination (Odds Ratio [OR], 0.78; 95% Credible Interval [CI], 0.66 - 0.92) and conception occurring (OR, 0.65; CI, 0.50 - 0.84) and transition from negative to non-negative MAP test status in the next 30 to 90 days. A positive association was observed between risk of insemination (OR, 1.34; CI, 1.16 - 1.52) and conception occurring (OR, 1.26; CI, 1.11 - 1.43) and transition from negative to non-negative MAP test status in the next 90 to 180 days. Current positive MAP test status was negatively associated with insemination risk (OR, 0.59; CI, 0.49 - 0.70) and positively associated with conception risk (OR, 1.12; CI, 0.96 - 1.30). Herd managers will have had access to test results, declaring cows with past recent or multiple positive MAP antibody ELISA results not to be bred, negatively influencing insemination risk. Overall, these results reveal complex temporal associations between a positive MAP antibody ELISA result and dairy cow fertility outcomes. This was identified particularly prior to a positive MAP antibody ELISA result, with risk of both insemination and conception increasing then decreasing before a non-negative MAP test status.
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