Abstr. M4 Merit of obtaining genetic evaluations of milk yield for each parity on Holstein bulls H.D. Norman, J.R. Wright,* R.L. Powell, and P.M. VanRaden Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350 INTRODUCTION Modeling separate PTA for each parity has become more frequent internationally Changes in mean records per daughter could affect bull PTA substantially if bulls have daughters that deviate from the typical response to aging DATA & METHODS (cont.) Assumed relationship among parities PTA1,2 = (n1PTA1 + n2PTA2)/(n1 + n2) PTA1,2,3 = (n1PTA1 + n2PTA2 + n3PTA3)/(n1 + n2 + n3) where n = number of daughters with records for parity 1, 2, or 3 Contribution of second and third parity alone predicted by 3 tailored genetic evaluations for each year PTA2 = [(n1 + n2)PTA1,2 – n1PTA1)]/n2 PTA3 = [(n1 + n2 + n3)PTA1,2,3 – n1PTA1 – n2PTA2]/n3 RESULTS (cont.) Tailored evaluations had higher correlations across time than did released USDA PTA for bulls with 500 daughters Standard deviations (kg) of differences between subsequent PTA milk by change in reliability Less variable bull PTA for all tailored evaluations than for released USDA PTA Among tailored evaluations, PTA stability increased with addition of later-parity information RESULTS (cont.) Regression analyses Coefficient of 0.725 for regression of both (PTA1,2 – PTA1) on (PTA1,2,3 – PTA1) and (PTA2 – PTA1) on (PTA3 – PTA1) Primarily the same genetic control for parities 2 and 3 PTA1,2 generally intermediate to PTA1 and PTA1,2,3 for bulls with 500 daughters PTA Evaluation year 1997 1998 1999 1 1996 0.995 0.993 0.992 0.997 1,2 0.994 0.996 1,2,3 0.998 2 0.989 3 0.984 0.983 Released 0.971 0.957 0.948 0.988 0.980 OBJECTIVES Examine differences among bulls in maturity rate of daughters Examine how those differences impact changes in bull evaluations across time Determine whether or not treating yield from different parities as a single trait is responsible for changes in genetic evaluations of high-reliability bulls Maturity rate1 (kg) Percentage of bulls with PTA2 Lower2 Intermediate2 Higher2 110 98 2 60 to 109 90 10 20 to 59 3 69 28 –10 to 19 27 21 53 –40 to –11 56 16 –80 to –41 89 1 –130 to –81 97 <–130 100 1PTA1,2,3 – PTA1 2Relative to PTA1 and PTA1,2,3 RESULTS Numbers of Holsteins bulls with 3 tailored genetic evaluations More uniformity in mean records per daughter across years for tailored PTA than for released USDA PTA for bulls with 500 daughters Evaluation year Number of daughters 10 500 1996 26,135 2567 1997 27,472 2665 1998 29,128 2757 1999 30,821 2864 DATA & METHODS Standardized milk records of Holstein cows grouped by year of first calving 1960–95 (evaluation year = 1996) 1960–96 (evaluation year = 1997) 1960–97 (evaluation year = 1998) 1960–98 (evaluation year = 1999) Three tailored genetic evaluations using current USDA-DHIA animal model methodology and records from various parities in the same herd First parity (PTA1) First and second parities (PTA1,2) First, second, and third parities (PTA1,2,3) Analysis repeated for each evaluation year for a total of 12 evaluations Evaluation years PTA Change in reliability (%) <5 5–9.9 10–14.9 15 1996–97 1 29 50 73 94 1,2 27 49 70 89 1,2,3 26 47 69 90 Released 44 76 109 159 1996–99 42 118 119 40 110 111 72 107 59 101 141 181 CONCLUSIONS Differences in maturity rate of daughters existed among bulls Those differences were consistent in one direction A single effect could be added to the evaluation model to account for differences in maturity rate Modification of the current evaluation model should reduce PTA fluctuations for individual bulls across time Evalua-tion year Records per daughter PTA1,2 PTA1,2,3 Released USDA PTA Mean SD 1996 1.72 0.04 2.21 0.09 2.60 0.50 1997 2.20 0.49 1998 0.10 0.48 1999 2.59 0.47