# Presentation: 700875

## Effect of service sireand cow sire ongestation length

- H.D. Norman,* J.R. Wright,
- P.M. VanRaden, and J.B. Cole
- Animal Improvement Programs Laboratory
- Agricultural Research Service, USDA
- Beltsville, MD 20705-2350
- dnorman@aipl.arsusda.gov

- Abstr. 230

## Objectives 

- Determine effect of bulls on gestation length
- Service (calf) sire
- Cow sire
- Improve accuracy of predicting calving date

## Data sources

- Lactation records from dairy records processing centers (DRPCs)
- Calving reports from the National Association of Animal Breeders
- Pedigree records from breed associations and DRPCs
- Breeding records from 2 DRPCs and Minnesota DHIA

## Data edits

- Inseminations after February 1998 that resulted in parturitions through December 2005 (>5 million calvings)
- Animals excluded if <87% breed purity based on AIPL crossbred database
- Secondary editing eliminated animals not bred to an identified AI bull

## Data

| Characteristic | Population |  |
| --- | --- | --- |
|  | Heifer | Cow |
| Records (no.) | 311,551 | 5,245,251 |
| Herd-years (no.)  | 17,551 | 141,008 |
| Bulls (no.) |  |  |
| ≥100 conceptions |  |  |
| All (no.) | 183 | 1,830 |
| Active AI (no.) | 53 | 103 |
| ≥500 conceptions |  |  |
| All (no.) | 61 | 525 |
| Active AI (no.) | 22 | 30 |

## Fixed effects in model

- Conception year
- Conception herd-year (absorbed)
- Conception month
- Age within parity
- Parturition status (multiple birth, calf gender)
- Lactation length
- Milk yield

- Discrete groups (no.)
- 	4	(heifers)
- 	8	(cows)
- 	12
- 	5	(heifers)
- 	17	(cows)
- 	8
- 	7
- 	5

## Random effects in model

- Service sire (direct)
- Cow sire (maternal)
- Cow
- Residual

## Analysis

- Bulls with ≥100 heifer and ≥100 cow conceptions
- All bulls (286 service sires, 348 cow sires)
- Heifers
- Cows
- Active-AI bulls (116 service sires, 54 cow sires)
- Heifers
- Cows
- Repeated for bulls with ≥500 heifer and ≥500 cow conceptions (132 service sires, 105 cow sires)

## Gestation length means (d)

| Popu-
lation | Ayrshire | Brown
Swiss | Guernsey | Holstein |  | Jersey |
| --- | --- | --- | --- | --- | --- | --- |
| Animals with data passing basic edits |  |  |  |  |  |  |
| Heifers | 282 | 287 | 285 | 278 |    2781⁄2 |  |
| Cows | 282 |    2871⁄2 | 286 |    2791⁄2 | 280 |  |
| Animals with added requirement
of an identified AI service sire |  |  |  |  |  |  |
| Heifers | — | 288 | — | 278 |    2781⁄2 |  |
| Cows | — | 288 | — |    2791⁄2 | 280 |  |

## Gestation length SD (d)

| Popu-
lation | Ayrshire | Brown
Swiss | Guernsey | Holstein |  | Jersey |
| --- | --- | --- | --- | --- | --- | --- |
| Animals with data passing basic edits |  |  |  |  |  |  |
| Heifers | 5.2 | 6.5 | 5.8 | 5.5 | 5.4 |  |
| Cows | 5.5 | 6.2 | 5.6 | 5.7 | 5.2 |  |
| Animals with added requirement
of an identified AI service sire |  |  |  |  |  |  |
| Heifers | — | 5.8 | — | 5.2 | 5.0 |  |
| Cows | — | 5.8 | — | 5.3 | 4.9 |  |

## Fixed effects results

- Conception year
- Conception month
- Age within parity
- Parturition status
- Lactation length
- Milk yield

- – Near 0
- – Summer calves arrive early
- – Younger animals calve sooner
- – Animals with twins calve early
- – Small negative effect
- – Small positive effect

## Heritability estimates

- Service sire
- Cow sire

- —  34%
- —  12%

## Gestation length PTA distribution

## Active AI Holstein PTA range

| Effect | PTA
population | Gestation length PTA (d) |  |
| --- | --- | --- | --- |
|  |  | Shortest | Longest |
| Service sire | Heifer | −4.2
O Man | 4.2
Mandelin |
|  | Cow | −5.3
Aspiration | 5.3
Sovereign |
| Cow sire | Heifer | −1.5
Darren | 2.6
Silky Gibson |
|  | Cow | −2.1
 O Man | 2.3
Shandy |

## SD (d) of gestation length PTA

| Effect | PTA population | Bulls with
≥100 conceptions |  |
| --- | --- | --- | --- |
|  |  | All | Active AI |
| Service sire | Heifer | 1.43 | 1.42 |
|  | Cow | 1.32 | 1.38 |
| Cow sire | Heifer | 0.75 | 0.74 |
|  | Cow | 0.76 | 0.65 |

## Heifer-cow PTA correlations

| Bull conceptions | PTA | Bull status |  |
| --- | --- | --- | --- |
|  |  | All | Active AI |
| ≥100 | Service sire | 0.96 | 0.96 |
|  | Cow sire | 0.83 | 0.77 |
| ≥500 | Service sire | 0.98 | 0.98 |
|  | Cow sire | 0.91 | 0.75 |

## Service sire-cow sire PTA correlations

| Bull
conceptions | PTA
population | Bull status |  |
| --- | --- | --- | --- |
|  |  | All | Active AI |
| ≥100 | Heifer | 0.61 | 0.37 |
|  | Cow | 0.71 | 0.71 |
| ≥500 | Heifer | 0.49 | 0.24 |
|  | Cow | 0.76 | 0.72 |

## Conclusions

- Bull differences exist and provide an opportunity to change gestation length
- Genetic evaluations based on heifers or cows highly correlated for both service sire and cow sire
- Genetic evaluations between service sire and cow sire moderately correlated for both heifers and cows

## Conclusions (continued)

- Genetic and environmental factors that impact gestation length helpful in predicting expected calving date
- More research needed to determine potential value of intentional selection for either shorter or longer gestation length in addition to selection for calving ease and stillbirth