# Presentation: 764901

## Genetic relationship of milk yield for different parities between bulls and their sons

## Objectives

**Determine whether bulls differ in maturity rate of their daughters**
**Confirm that those differences are transmitted across generations**

## Data

**Standardized lactation milk records for Holstein parities 1 through 3**
**Cows first calving between 1960 and 1998**
**No missed parities before cow exited herd**
**Only records from first herd included**

## Methods

**	****Three PTA calculated for each bull using current USDA-DHIA animal model**
**	****PTA****1**** based on records from parity 1 of daughters and their contemporaries**
**	****PTA****1,2**** based on records from parities 1 and 2 of daughters and their contemporaries**
**	****PTA****1,2,3**** based on records from parities 1, 2, and 3 of daughters and their contemporaries**

## Methods (cont.)

**	****Number of records**
**	****n****1**** = number of bull’s daughters with first parity records**
**	****n****2**** = number of bull’s daughters with second parity records**
**	****n****3**** = number of bull’s daughters with third parity records**

## Methods (cont.)

**	****Solutions for biological contributions of parities 2 (****PTA****2****) and 3 (****PTA****3****) derived from                   **

## Results

**2864 bulls with genetic evaluations based on ********500 daughters **
**Difference between PTA****1**** and PTA****1,2,3**** ranged from ********290**** to ****295**** kg of milk; SD of ****85**** kg**
**Difference between PTA****1**** and PTA****3**** ranged from ********610**** to ****555**** kg of milk; SD of ****179**** kg**

## Results (cont.)

**PTA****1,2**** intermediate to PTA****1**** and PTA****1,2,3**
**(PTA****1,2**** ******** PTA****1****) regressed on (PTA****1,2,3**** ******** PTA****1****)**
**b = ****0.725****,  R = ****0.971**** **
**(PTA****2**** ******** PTA****1****) regressed on (PTA****3**** ******** PTA****1****) **
**b = ****0.725****,     R = ****0.852**** **
**Primarily same genetic control for parities     2 and 3**

## Impact of daughter maturity rate

| PTA1,2,3 PTA1 (kg) |  |  |  | Number of bulls with PTA1,2 as: |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  |  |  |  |  | Lowest1 | Intermediate1 | Highest1 |
| 110 |  |  |  | 0 |  | 227 | 4 |
| 60 | to | 109 |  | 0 |  | 314 | 35 |
| 20 | to | 59 |  | 11 |  | 274 | 112 |
| 10 | to | 19 |  | 106 |  | 82 | 209 |
| 40 | to | 11 |  | 122 |  | 238 | 69 |
| 80 | to | 41 |  | 47 |  | 402 | 5 |
| 130 | to | 81  |  | 12 |  | 369 | 1 |
| 130 |  |  |  | 1 |  | 224 | 0 |
| 1Relative to PTA1 and PTA1,2,3
 |  |  |  |  |  |  |  |

## Correlation between parity PTA for milk (1996 vs 1999) 

| Trait | r  | SD of difference (kg) |
| --- | --- | --- |
| PTA1 | 0.992 | 27 |
| PTA1,2 | 0.994 | 31 |
| PTA1,2,3 | 0.994 | 32 |
| PTA2 | 0.989 | 45 |
| PTA3 | 0.983 | 63 |
| PTAPublished | 0.948 | 88 |

## Results (cont.)

**16,643 sons with genetic evaluations based on ********40 daughters**
**Expected regressions of son PTA on sire PTA (calculated within sire and son birth year) between 0.44 and 0.50**
**Actual regressions near expectations**

## Regression of son PTA on sire PTA for milk yield

| Trait | Regression | SE |
| --- | --- | --- |
| PTA1 | 0.44 | 0.01 |
| PTA1,2 | 0.43 | 0.01 |
| PTA1,2,3 | 0.43 | 0.01 |
| PTA1,2  PTA1 | 0.43 | 0.01 |
| PTA1,2,3  PTA1 | 0.43 | 0.01 |
| PTA1,2,3  PTA1,2 | 0.42 | 0.02 |

## Regression of son PTA on sire PTA for milk yield (cont.)

| Trait | Regression | SE |
| --- | --- | --- |
| PTA1 | 0.44 | 0.01 |
| PTA2 | 0.42 | 0.01 |
| PTA3 | 0.44 | 0.01 |
| PTA2  PTA1 | 0.44 | 0.01 |
| PTA3  PTA1 | 0.45 | 0.01 |
| PTA3  PTA2 | 0.43 | 0.03 |

## Conclusions

**Differences in daughter maturity rate are large enough to impact evaluation accuracy, if genetic.**
**Differences are transmitted from sires to sons (genetic confirmation).**

## Conclusions

**Modeling separate PTA for each parity should:**
**Increase accuracy of genetic evaluations**
**Reduce oscillation in bull evaluations when records per daughter change considerably**
**Most noticeable in high reliability bulls**