# Presentation: 103219

## Genetic Evaluation of Calving Traits in US Holsteins

## Introduction

**National evaluations were introduced for Holstein calving ease (****CE****) in August 2002 and for stillbirth (****SB****) in August 2006.**
**A calving ability index (****CA$****) which includes SB and calving ease (****CE****) was developed.**
**Relationships among calving traits and other diseases are being studied.**

## Why the concern?

**Calving difficulty and stillbirth are expensive (Dematawewa and Berger, 1997; Meyer et al., 2001)**
**There is concern that rates of dystocia and stillbirth are increasing**
**Lactations initiated with dystocia have higher risks for other diseases (Cole et al., unpublished data).**

## How do the evaluations work?

**Funded by the National Association of Animal Breeders**
**Data are collected from multiple sources:**
**Pedigree from breed associations**
**Calving data from DRPC**
**Evaluated using a sire-maternal grandsire threshold model**

## Threshold model

**Scores assumed to be observations on a continuous underlying scale**
**Thresholds relate scores to underlying scale:**

**Allows for differences in amount of change between consecutive scores**

**Observed scores**

## Calving ease definition

**Reported on a five-point scale:**
**	****	****1 = No problem**
**	****	****2 = Slight problem**
**	****	****3 = Needed assistance**
**	****	****4 = Considerable force**
**	****	****5 = Extreme difficulty**
**Scores of 4 and 5 are combined**

## Stillbirth definition

**Reported on a three-point scale:**
**Scores of 2 and 3 are combined**

| 1 = calf born alive, |
| --- |
| 2 = calf born dead, |
| 3 = calf died within 48 h of parturition. |

## Distribution of SB and CE Scores

- Calving Ease Score

- Stillbirth Score

## Stillbirth records by lactation

## Data and edits

**7 million**** SB records were available for Holstein cows calving since 1980**
**Herds needed ≥10 calving records with SB scores of 2 or 3 for inclusion**
**Herd-years were required to include ≥20 records**
**Only single births were used (no twins)**

## Sire-MGS threshold model

**Implemented for calving ease (Aug 2002) and stillbirth (Aug 2006)**
**Sire effects allow for corrective matings in heifers to avoid large calves**
**MGS effects control against selection for small animals which would have difficulty calving**

## Genetic evaluation model

**A sire-maternal grandsire (****MGS****) threshold model was used:**
**Fixed:**** year-season, parity-sex, sire and MGS birth year**
**Random:**** herd-year, sire, MGS**
**(Co)variance components were estimated by Gibbs sampling**
**Heritabilities are ****3.0%**** (direct) and ****6.5%**** (MGS)**

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## Trait definition

**PTA are expressed as the expected percentage of stillbirths**
**Direct**** SB measures the effect of the calf itself**
**Maternal**** SB measures the effect of a particular cow (daughter)**
**A base of ****8%**** was used for both traits:**
**Direct:**** bulls born 1996****–****2000**
**Maternal:**** bulls born 1991****–****1995**

## Phenotypic trend for stillbirths

## Genetic trend for stillbirths

## Distribution of PTA

## Distribution of reliabilities

## Dystocia and stillbirth

**Meyer et al. (2001) make a strong argument for the inclusion of dystocia in models for SB**
**Difficulty of interpretation**** - formidable educational challenge**
**Interbull trait harmonization**** - none of the March 2006 test run participants included dystocia in their models**
**Changes in sire and MGS solutions on the underlying scale between models were small**

## Evaluation conclusions

**Reliabilities for SB averaged ****45%**** versus ****60%**** for CE**
**Phenotypic and genetic trends from 1980 to 2005 were both small**
**An industry-wide effort is currently underway to improve recording of calf livability**

## Index data

**Same initial dataset as BV estimation**
**Calvings with unknown MGS were eliminated for VCE**
**Records with sire and MGS among the ****2,600**** most-frequently appearing bulls were selected**
**2,083,979**** calving records from ****5,765**** herds and ****33,304**** herd-years**

## Sampling

**Six datasets of ****~250,000**** records each were created by randomly sampling herd codes without replacement**
**Datasets ranged from ****239,192**** to ****286,794**** observations, and all averaged ****7%**** stillbirths**
**A common pedigree file was used to facilitate comparisons between sire and MGS solutions**

## Heritabilities

**Calving Ease (Direct)****	****	****8.6%**
**Calving Ease (MGS)****	****	****3.6%**
**Stillbirth (Direct)****	****	****	****3.0%**
**Stillbirth (MGS)****	****	****	****6.5%**

## Genetic correlations among SB and CE

| Trait |  | CE |  |  | SB |  |
| --- | --- | --- | --- | --- | --- | --- |
|  |  | Direct | Maternal |  | Direct | Maternal |
| CE | Direct | 1.00 | 0.46 |  | 0.67 | 0.25 |
|  | Maternal |  | 1.00 |  | 0.29 | 0.63 |
| SB | Direct |  |  |  | 1.00 | 0.28 |
|  | Maternal |  |  |  |  | 1.00 |

## Economic assumptions

**Newborn calf value**
**Expenses per difficult birth (CE ≥4) **

| $450 for females |
| --- |
| $150 for males |

| $75 labor and veterinary |
| --- |
| $100 reduced milk yield |
| $75 reduced fertility and longevity |
| 1.5% chance of cow death ($1800) |

## Calving Ability index

**CA$ has a genetic correlation of ****0.85**** with the combined direct and maternal CE values in 2003 NM$ and ****0.77**** with maternal CE in TPI**
**Calving traits receive ****6%**** of the total emphasis in NM$ (August 2006 revision)**

## Breeds other than Holstein

**Brown Swiss**** economic values are   ****−6**** for SCE and ****−8**** for DCE**
**Separate SB evaluations are not available**
**CE values include the correlated response in SB**
**Other breeds**** will be assigned CA$ of ****0**

## Health and calving traits

**Health event data from on-farm computer systems**
**Events arranged in putative causal order by DIM at first occurrence**
**Path analysis to determine associations among disorders**
**Significant associations shown in following tables (****P < 0.05****)**

## Health and dystocia

| Disorder | DIM | Odds Ratio |
| --- | --- | --- |
| Stillbirth | 1 | 39.0 |
| Retained placenta | 1 | 3.8 |
| Mastitis (0—30 d) | 6 | 2.3 |
| Ketosis | 11 | 3.1 |
| Metritis | 16 | 3.9 |
| Reproductive | 32 | 2.3 |
| Displaced abomasum | 29 | 2.2 |
| Respiratory | 44 | 3.0 |

## Health and stillbirth

| Disorder | DIM | Odds Ratio |
| --- | --- | --- |
| Retained placenta | 1 | 2.8 |
| Mastitis (0—30 d) | 6 | 2.4 |
| Metritis | 16 | 2.1 |
| Displaced abomasum | 30 | 2.3 |
| Reproductive | 32 | 3.4 |
| Digestive | 52 | 2.8 |

## Conclusions

**A routine evaluation for stillbirth in US Holsteins was implemented in August 2006**
**Direct and maternal stillbirth were included in NM$ for Holsteins starting in August 2006**
**The US participates in routine Interbull evaluations that began in November 2006**
**Calving problems increase lifetime health care costs and decrease profitability**

## Acknowledgments

**Jeff Berger, Iowa State University**
**John Clay, Dairy Records Management Systems**
**Ignacy Misztal and Shogo Tsuruta, University of Georgia**
**National Association of Animal Breeders**