# Presentation: 681165

## Impact of selection for increased daughter fertility on productive life and culling for reproduction

*H. D. Norman, J. R. Wright*, R. H. Miller*
- Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350

- Abstract T19

- _INTRODUCTION_
- Improving reproductive traits through genetic selection was usually considered futile because of low heritability (<5%).
- Pregnancy rate declined by 7% and days open increased by 39 days from 1960 To 2000.
- AIPL began calculating genetic evaluations for daughter pregnancy rate (DPR) in 2003.

- _OBJECTIVE_
- Determine how effective emphasis on DPR for two generations was in changing fertility and productive life (PL).

- _CONCLUSIONS_
- Emphasis on DPR for 2 generations increased PL and decreased culling for reproduction.
- Selection for PTA DPR can be effective               in improving fertility.

- _DATA & METHODS_
- Data edits:
- Holstein AI bulls with January 2008 PTA DPR based on 35 daughters.
- Holstein cows with birth dates from 1988 through 1999 and calving dates from 1990 through 2005.
- Cows excluded if they changed herds, had missing lactation records within first 5 parities, or were in herds with <10 cows.
- Final data set of 4,380,300 cows in 31,759 herds.
- Bulls assigned to 5 groups (quintiles) based on their PTA DPR.
- Cows divided into 25 groups based on their sire and maternal grandsire (MGS) quintile for PTA DPR.
- Examples:
- Cows in group 1,1 had both sires and MGS in the lowest 20% of AI bulls for PTA DPR
- Cows in group 5,5 had both sires and MGS in the highest 20% of AI bulls for PTA DPR

- http://aipl.arsusda.gov/

- _RESULTS_
- Number of cows by ancestor PTA DPR group

- 2008

|  |  |  |  |
| --- | --- | --- | --- |
|  |  |  |  |
|  |  |  |  |
|  |  |  |  |

- Percent cows reported culled for reproduction by ancestor PTA DPR group

|  | 1 | 2 | 3 | 4 | 5 |
| --- | --- | --- | --- | --- | --- |
| 1 | 238,632 | 205,810 | 191,135 | 243,969 | 286,418 |
| 2 | 182,663 | 152,309 | 144,732 | 187,714 | 224,411 |
| 3 | 150,574 | 130,472 | 127,804 | 158,923 | 204,809 |
| 4 | 162,177 | 136,933 | 132,426 | 171,166 | 218,873 |
| 5 | 133,636 | 117,151 | 114,308 | 151,456 | 211,799 |

- Distribution of cows by group ranged from 2.6% to 6.5%, most likely due to heavy use of certain bulls.
- Sire and MGS PTA DPR mean by group  (not shown) varied by over 4% (from -2.1 in group 1,1 to 2.1 in group 5,5).

- PL was over 4 mo longer for cows with sires and MGS from the highest group than those from the lowest group.
- Sire quintile had a larger effect on increasing length of PL (2.8 to 3.3 mo) than MGS quintile (0.8 to 1.4 mo).

- Frequency of culling for reproductive reasons decreased over 3% from 13.1% (group 1,1) to 10.0% group (5,5).

- Mean 1st parity pregnancy rate by ancestor PTA DPR group

- First parity pregnancy rate rose from 20.0% for cows sired by the lowest PTA DPR ancestor group  (1,1) to 27.3% for cows sired by highest (5,5).

|  | 1 | 2 | 3 | 4 | 5 |  |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | -4.2 | -3.8 | -3.7 | -3.3 | -2.8 | 1.4 |
| 2 | -3.0 | -2.5 | -2.5 | -1.9 | -1.5 | 1.4 |
| 3 | -2.9 | -2.5 | -2.5 | -2.2 | -1.7 | 1.3 |
| 4 | -2.1 | -1.7 | -1.6 | -1.4 | -0.9 | 1.2 |
| 5 | -0.8 | -0.6 | -0.6 | -0.3 | 0.0 | 0.8 |
|  | 3.3 | 3.2 | 3.1 | 3.0 | 2.8 |  |

- MGS quintile

- Sire quintile

- Max. sire difference

- Max. MGS differ-ence

- Pregnancy rate (%)

- MGS quintile

- Least-squares differences  for percent culled for reproduction

|  | 1 | 2 | 3 | 4 | 5 |  |
| --- | --- | --- | --- | --- | --- | --- |
| 1 | 1.9 | 1.7 | 1.5 | 1.2 | 1.1 | 0.8 |
| 2 | 1.6 | 1.3 | 1.2 | 1.0 | 0.9 | 0.7 |
| 3 | 1.2 | 1.1 | 0.8 | 0.7 | 0.5 | 0.7 |
| 4 | 0.6 | 0.5 | 0.3 | 0.1 | 0.2 | 0.4 |
| 5 | 0.4 | 0.3 | 0.2 | 0.0 | 0.0 | 0.4 |
|  | 1.5 | 1.4 | 1.3 | 1.2 | 1.1 |  |

- MGS quintile

- Sire quintile

- Cows with low ancestor PTA DPR were culled for reproduction at a 2% higher rate than those with high ancestor PTA DPR.
- Sire quintile and MGS quintile effect were nearly linear across groups.

- Max. MGS differ-ence

- Max. sire difference

- _DATA & METHODS (__*cont.*__)_
- Analysis:
- Examine least-squares differences between cow groups on a within-herd basis with cow birth year in the model.

- Sire quintile

- _RESULTS (__*cont.)*_
- Mean of cow PL by ancestor PTA DPR group

- _RESULTS (__*cont.)*_
- Least-squares differences for PL (mo)

- Overall productive life mean was 27.0 months.
- Cows in the lowest PTA DPR ancestor group (1,1) had a mean PL of 25.0 while the highest group averaged 28.7 months.
- The increase in PL was similar to the increase seen in first parity pregnancy rate.
- First parity mature-equivalent milk mean was 1,230 kg lower in the highest PTA DPR group (5,5) than in the lowest (1,1).

- PL (mo)

- % culled