# Presentation: 668489

## Merit of obtaining genetic evaluations of milk yield for each parity on Holstein bulls

- 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

*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

- Abstr. M4

- 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

- 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

- 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

| Evaluation year | Number of daughters |  |  |
| --- | --- | --- | --- |
|  | 10 | 500 |  |
| 1996 | 26,135 | 2567 |  |
| 1997 | 27,472 | 2665 |  |
| 1998 | 29,128 | 2757 |  |
| 1999 | 30,821 | 2864 |  |

| Evalua-tion
year | Records per daughter |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  | PTA1,2 |  |  | PTA1,2,3 |  |  | Released USDA PTA |  |  |
|  | Mean | SD |  | Mean | SD |  | Mean | SD |  |
| 1996 | 1.72 | 0.04 |  | 2.21 | 0.09 |  | 2.60 | 0.50 |  |
| 1997 | 1.72 | 0.04 |  | 2.20 | 0.09 |  | 2.60 | 0.49 |  |
| 1998 | 1.72 | 0.04 |  | 2.20 | 0.10 |  | 2.60 | 0.48 |  |
| 1999 | 1.72 | 0.04 |  | 2.20 | 0.10 |  | 2.59 | 0.47 |  |

- 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

- 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

| PTA | Evaluation year | Evaluation year |  |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  | 1997 | 1998 | 1999 |  |
| 1 | 1996 | 0.995 | 0.993 | 0.992 |  |
|  | 1997 |  | 0.997 | 0.995 |  |
|  | 1998 |  |  | 0.997 |  |
| 1,2 | 1996 | 0.995 | 0.994 | 0.994 |  |
|  | 1997 |  | 0.997 | 0.996 |  |
|  | 1998 |  |  | 0.997 |  |
| 1,2,3 | 1996 | 0.995 | 0.994 | 0.994 |  |
|  | 1997 |  | 0.998 | 0.997 |  |
|  | 1998 |  |  | 0.998 |  |
| 2 | 1996 | 0.989 | 0.989 | 0.989 |  |
|  | 1997 |  | 0.995 | 0.994 |  |
|  | 1998 |  |  | 0.994 |  |
| 3 | 1996 | 0.989 | 0.984 | 0.983 |  |
|  | 1997 |  | 0.993 | 0.989 |  |
|  | 1998 |  |  | 0.992 |  |
| Released | 1996 | 0.971 | 0.957 | 0.948 |  |
|  | 1997 |  | 0.988 | 0.980 |  |
|  | 1998 |  |  | 0.992 |  |

| 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 | 1 | 42 | 76 | 118 | 119 |  |
|  | 1,2 | 40 | 73 | 110 | 111 |  |
|  | 1,2,3 | 40 | 72 | 107 | 111 |  |
|  | Released | 59 | 101 | 141 | 181 |  |

| Maturity rate1 (kg) | Percentage of bulls with PTA2 |  |  |  |
| --- | --- | --- | --- | --- |
|  | Lower2 | Intermediate2 | Higher2 |  |
| 110 | 0 | 98 | 2 |  |
| 	60	to	109 | 0 | 90 | 10 |  |
| 	20	to	59 | 3 | 69 | 28 |  |
| 	–10	to	19 | 27 | 21 | 53 |  |
| 	–40	to	–11 | 28 | 56 | 16 |  |
| 	–80	to	–41 | 10 | 89 | 1 |  |
| 	–130	to	–81 | 3 | 97 | 0 |  |
| <–130 | 0 | 100 | 0 |  |
| 1PTA1,2,3 – PTA1
2Relative to PTA1 and PTA1,2,3 |  |  |  |  |

- 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