1. 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
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 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