Genetic Evaluation of Stillbirth in US Holsteins Using a Sire-maternal Grandsire Threshold Model

1. Genetic Evaluation of Stillbirth in US Holsteins Using a Sire-maternal Grandsire Threshold Model

2. Introduction • Stillbirth is a genetically-controlled trait. • Producers are concerned about stillbirth. • Calf livability scores are already delivered with calving ease data. • Participation in Interbull evaluations for both calving ease (CE) and stillbirth (SB) is desirable.

3. Stillbirth Definition • Reported on a three-point scale: • Scores of 2 and 3 are combined.

4. Data and Edits • 6 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).

5. Stillbirth Data Stillbirth Score

6. 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).

7. 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.

8. Phenotypic Trend for Stillbirths

9. Genetic Trend for Stillbirths

10. Distribution of PTA

11. Distribution of Reliabilities

12. Dystocia and Stillbirth • Meyer et al. (2001b) 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.

13. Correlations among domestic and Interbull SB solutions (≥90% Rel on both scales)

14. Genetic Correlations Among SB and CE

15. 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).

16. Conclusions • Number of SB records (6 million) was about half of calving ease records (14 million). • 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 underway to improve recording of calf livability.

17. 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. • August 2006 data were sent to Interbull for the September 2006 test run for calving traits. • The US will participate in routine Interbull evaluations beginning in November 2006.

18. Acknowledgments • Jeff Berger, Iowa State University • John Clay, Dairy Records Management Systems • Ignacy Misztal and Shogo Tsuruta, University of Georgia