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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.
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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and stillbirth are increasing • Lactations initiated with dystocia have higher risks for other diseases (Cole et al., unpublished data).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
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
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
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)
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
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%
Economic assumptions • Newborn calf value • Expenses per difficult birth (CE ≥4)
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)
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