# Presentation: 504139

## R.H. Miller,,1 H.D. Norman,1 and J.S. Clay 2 
1Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350;
 2North Carolina State University, Raleigh, NC 27603‐3435

- 1Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350;
-  2North Carolina State University, Raleigh, NC 27603‐3435

- Abstr.
- 1390

- Factors affectingfertility traitsof Holsteinsand Jerseys

## INTRODUCTION

- Data on fertility would allow the development of genetic evaluations and economic indexes that could be used to offset the decline in reproductive performance associated with selection for high yield.
- Female fertility already is evaluated in several nations; U.S. international competitiveness might improve if U.S. progeny-test programs provided fertility data.
- Research is needed to model genetic and environmental factors that affect fertility, to determine value of genetic gains for reproduction, and to determine how breeders should balance long term goals.

## OBJECTIVES

- To assess effects on fertility of:
- Stage of lactation at first service.
- Parity and age within parity.
- Peak test-day yield for milk, fat, and protein.

## DATA

- Records from 3.6 million Holstein and 0.26 million Jersey lactations in 17,445 and 1177 herds, respectively, in 47 States.
- First services (Jan. 1995 – Dec. 2000).
- AI service date and service sire ID.
- Milk, fat, and protein yields for first 3 test days of lactation.

## DATA (cont.)

- Fertility traits:
- Nonreturn to first service within 70 d.
- Number of services.
- Days to first service.
- Days to last service.
- Calving interval if subsequent calving.
- Data edits:
- Test-day yields: 4.5-109 kg for milk and 0.91-3.63 kg for fat and protein.
- Mean herd-year nonreturn rate: 0.10-0.90.
- Calving interval designated as missing if gestation length <260 d or >302 d.

## ANALYSIS

- Least squares by breed with herd-year-month of first service absorbed.
- Model:
- Lactation stage at first service (11 groups) for nonreturn rate and number of services.
- Parity (1, 2, ... 5, >5).
- Partial regression on peak test-day yield (milk, fat, and protein mean from 2 test days with highest energy-corrected milk among first 3 test days).
- Partial regression on deviation of calving age from mean calving age for that parity.
- Alternative model for season: only herd-years absorbed and effect of calendar month of first service included.

## RESULTS

|  | Holstein |  |  | Jersey |  |
| --- | --- | --- | --- | --- | --- |
| Trait | X | SD |  | X | SD |
| Nonreturn rate | 0.55 | 0.48 |  | 0.57 | 0.47 |
| Number of services | 2.1 | 1.3 |  | 2.0 | 1.3 |
| Days to first service | 90 | 35 |  | 83 | 31 |
| Days to last service | 141 | 75 |  | 125 | 69 |
| Calving interval (d) | 410 | 66 |  | 397 | 60 |

- Means and standard deviations:

## RESULTS (cont.)

- RESULTS *(cont.)*

- Least-squares estimates:
- Effect of lactation stage on nonreturn rate:

## Least-squares estimates: (cont.)
Effect of lactation stage on number of services:

- Effect of lactation stage on number of services:

- RESULTS *(cont.)*

## RESULTS (cont.)

- Least-squares estimates:
- Effect of calendar month at first service on nonreturn rate:

## RESULTS (cont.)

| Trait | Milk | Fat | Protein |
| --- | --- | --- | --- |
| Holstein |  |  |  |
| Nonreturn rate | -0.002 | -0.019 | 0.029 |
| Number of services | 0.016 | 0.096 | -0.168 |
| Days to first service | 0.88 | 0.53 | -27.38 |
| Days to last service | 1.82 | 5.53 | -37.19 |
| Calving interval (d) | 1.83 | 5.94 | -43.72 |

- RESULTS *(cont.)*

- Partial regressions of fertility traits on peak test-day yield (kg/d):

## RESULTS (cont.)

- Partial regressions of fertility traits on peak test-day yield (kg/d): *(cont.)*

| Trait | Milk | Fat | Protein |
| --- | --- | --- | --- |
| Jersey |  |  |  |
| Nonreturn rate | -0.003 | -0.048 | 0.062 |
| Number of services | 0.022 | 0.170 | -0.286 |
| Days to first service | 0.89 | -1.53 | -16.14 |
| Days to last service | 1.97 | 4.60 | -28.86 |
| Calving interval (d) | 2.05 | 3.63 | -30.01 |

## CONCLUSIONS

- Slightly higher fertility for Jerseys than for Holsteins, but first service later during first lactation.
- Markedly lower fertility for first service at <90 DIM for Holsteins and at <50 d for Jerseys.
- Highest fertility generally in parity 3.
- Lowest fertility during summer and early fall; highest during spring.
- Decline in fertility with increase in peak yield.