Sire Verification in Multi-Sire Breeding Systems

The objective of this study was to evaluate the use of DNA parentage testing on commercial cow-calf operations using multi-sire breeding pastures and to determine associations between phenotypic and spermatological traits of bulls and number of calves sired. Seven breeding pastures located within 4 commercial Saskatchewan ranches cooperated in this study. Calves and bulls were DNA parentage tested to determine sires. Data were analysed using Chi square procedures. Bulls sired a significantly different (P<0.01) number of calves compared to expected in 5 of the breeding pastures. Bull age was found to significantly (P<0.01) affect bull prolificacy. All bulls were required to pass a breeding soundness exam (BSE) before entering a breeding pasture so no association was found between either scrotal circumference (R² = 0.04) or percent normal sperm (R²=0.13). Economic models were developed to evaluate the value of adopting this technology on farm. One model showed that bulls who sired more calves had a lower cost per calf sired. Another model showed that using parentage testing to identify bulls causing dystocia, by testing calves from difficult births and then culling the responsible bull can provide an economic return on investment to the farm. Results also show that a producer could reduce testing costs by up to 70% by only testing calves born in week 3 and still obtain results that correctly identify low and high prolificacy sires. Only testing a sample of the calf crop also ensures lab results obtained in time to make changes to the bull battery ahead of the next breeding season. Real value from parentage testing comes from being able to couple sire parentage with other basic production records. There is potential to increase overall bull prolificacy in a herd and increase other economically important traits by using DNA parentage to aid in sire selection.