Genetic Evaluation of Calving Traits in US Holsteins

1. Genetic Evaluation of Calving Traits in US Holsteins

2. 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.

3. 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and stillbirth are increasing • Lactations initiated with dystocia have higher risks for other diseases (Cole et al., unpublished data).

4. 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

5. 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

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

7. 0 1 2 3 Total 1 1,287,290 4,343,140 158,250 20,418 5,809,098 2 203,738 482,720 49,858 2,537 738,853 3 183,951 375,203 70,522 3,353 633,029 4 59,614 108,037 37,851 1,740 207,242 5 23,690 38,929 32,196 1,272 96,087 Total 1,758,283 5,348,029 348,677 29,320 7,484,309 Distribution of SB and CE Scores Stillbirth Score Calving Ease Score

8. Stillbirth records by lactation

9. 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)

10. 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

11. 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)

12. 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

13. Phenotypic trend for stillbirths

14. Genetic trend for stillbirths

15. Distribution of PTA

16. Distribution of reliabilities

17. 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

18. 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

19. 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

20. 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

21. Heritabilities • Calving Ease (Direct) 8.6% • Calving Ease (MGS) 3.6% • Stillbirth (Direct) 3.0% • Stillbirth (MGS) 6.5%

22. Genetic correlations among SB and CE

23. Economic assumptions • Newborn calf value • Expenses per difficult birth (CE ≥4)

24. 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)

25. 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

26. 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)

27. Health and dystocia

28. Health and stillbirth

29. 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

30. 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