Within birth year correlations of parity differences between countries by number of daughters

1. Comparison of maturity rate for bull daughters in the United States and Canada H.D. Norman1, J.R. Wright1,* R.L. Powell1, P.M. VanRaden1, and F. Miglior2,3 1Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350 2Agriculture and Agri-Food Canada – Dairy and Swine Research and Development Centre, Lennoxville, QC, Canada 3Canadian Dairy Network, Guelph, ON Canada Abstr. M20 INTRODUCTION • Many countries in Interbull calculate genetic evaluations for individual parities to consider differences in rate of maturity. • In Canada, genetic evaluations are calculated with a multi-trait parity model. • In the U.S., official genetic evaluations are calculated with a single-trait repeatability model. • Recent U.S. studies show that apparent differences in maturity rate of bulls’ daughters are contributing to variation in USDA PTAs across time. • Examining apparent differences in rate of maturity in two populations should provide evidence to determine whether the observed differences are genetic. DATA & METHODS (cont.) Canada data: • Estimated Breeding Values (EBV) from published November 2004 CDN evaluation using test day model converted to predicted transmitting ability (divided by 2) • Standardized first parity (CAN1) • Standardized second parity (CAN2) • Standardized third parity (CAN3) Methods Genetic evaluation subsets: Analysis was run on three groups of bulls: • 20 or more daughters in both countries (804 bulls) • 100 or more daughters in both countries (403 bulls) • 500 or more daughters in both countries (131 bulls) Within birth year correlations between parity specific evaluations (bulls with >=100 daughters above the diagonal, those with >=500 below Within birth year correlations of parity differences between countries by number of daughters Min. no. of daus. Trait differences Corr. Reg. 20 US2 - US1 and CAN2 - CAN10.63 0.63 US3 - US1andCAN3 - CAN1 0.53 0.55 US3 – US2andCAN3 – CAN2 0.14 0.08 100 US2 - US1 and CAN2 - CAN1 0.81 0.83 US3 - US1andCAN3 - CAN1 0.75 0.78 US3 – US2andCAN3 – CAN2 0.24 0.14 500 US2 - US1 and CAN2 - CAN1 0.89 0.98 US3 - US1andCAN3 - CAN1 0.84 0.91 US3 – US2andCAN3 – CAN2 0.55 0.50 RESULTS • Correlations were highest between parity 2 and 3 within (0.92 to 0.98) and across countries (0.89 To 0.92). • Correlations were lowest between parity 1 and 3 within (0.83 to 0.88) and across countries (0.79 to 0.86). • Correlation were high between evaluations for the same parity across countries (0.90 to 0.96) • Correlations between Canadian parity EBVs were higher than between US parity PTAs, due in part to the genetic correlations matrix assumed between lactations. • Correlations observed between parities were considerably higher than those assumed in the evaluation model. • Regressions (not shown) were from 0.90 to 1.00, and slightly higher for US PTAs than for Canadian EBVs. Standard errors ranged from 0.01 to 0.04. RESULTS (cont.) • Correlations between parity differences were highly related to number of daughters and records included. • Evaluations of parities with the highest genetic correlations had the lower correlations between their differences across countries OBJECTIVES • Compare apparent differences in maturity rate of bulls’ daughters across countries to determine if they are consistent. RESULTS • Average number of lactations or test days DATA & METHODS US data: • Three predicted transmitting abilities (PTA) were created using current USDA-DHIA animal model methodology • Data were Holstein cows first calving 1960-1998 • PTAs included either first parity (US1,), first and second parity (US1,2), or first, second and third parity records (US1,2,3) • Contributions of second and third parity alone (US2, US3) were derived from the other three by weighting for the numbers of daughters/records in each parity CONCLUSIONS • Correlations between genetic evaluations from the two countries were high. • Differences in apparent rate of maturity observed were highly correlated, providing convincing evidence that the differences observed are genetic.