Sire verification in multi-sire breeding systems

Abstract

An experiment was conducted to evaluate using DNA parentage testing on commercial cow-calf operations using multi-sire breeding groups to determine the associations between various traits of bulls and number of calves sired. Four commercial Saskatchewan ranches with 7 breeding groups collaborated in this study, where all potential sires and progeny were sampled to determine the sire of each calf. Expected vs observed calf data were analyzed using Chi-square analysis. In all but 2 of the 7 breeding groups, it was determined that each bull sired a different (P<0.01) number of calves. Age of sire was found to effect (P<0.01) bull prolificacy or number of calves sired. A bull prolificacy index (BPI) was developed to compare which bulls are siring more or less than expected number of progeny. All bulls were required to pass a breeding soundness exam (BSE) before breeding season, therefore weak correlations were found between scrotal circumference (R2=0.04) or percent normal sperm (R2=0.13) and BPI values. No sire match ranged from 2-7% of calves tested. Testing only calves born in the 3rd week of calving, indicated that bulls could be assigned accurately to high or low prolificacy categories, but bulls with the fewest number of calves sired could not be detected. Economic models were developed to evaluate the value of adopting parentage testing on farm using a cost benefit analysis. The model showed bulls that sired more calves had a lower cost per calf sired. Based on the model, if bulls were siring < 25 calves it would be more economical to use AI in the breeding program. The model also determined that if one bull was causing increased dystocia rates in a herd, testing calves from difficult births to cull responsible bulls did provide an economic return on investment to the operation. 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.