Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2007
Publication Date: July 8, 2007
Citation: Powell, R.L., Norman, H.D., Wright, J.R. 2007. Relationship of gestation length to stillbirth. Journal of Dairy Science. 90(Suppl. 1):16(abstr. M39). Technical Abstract: Stillbirth (SB) genetic evaluations recently instituted reflect increased interest in broadening the array of traits considered in assessing overall genetic merit. Gestation length (GL) is not yet evaluated in the United States, but has economic and managemental impacts. The relationship of SB with dystocia is in many reports, but there is less information with gestation length. Data were from USDA files of more than 8 million Holstein cows calving from 1999 through 2005. The GL were limited to those 260-295 d. Herds were included if they had at least 15 stillbirth records and 3 stillbirths. The mean SB rate was examined by gestation length. Cows with GL of <270 d had 17.8% stillbirths, those with GL of 278 to 282 d had 5.0%, while those with >290 d had 8.1%. Heritabilities for SB were computed with a linear model including fixed effects of calving herd-year, year, age-parity, offspring code (gender and number), lactation length, milk yield group, and random effects of cow, sire of cow, and service sire. Heritabilities for service sire and sire of cow effect for the binomial SB trait were 0.006 and 0.012 which corresponded to 0.023 and 0.046 on the assumed underlying scale. Bull evaluations for GL were computed by a linear model with the same factors as for estimating SB heritability. Correlations of those GL evaluations and official February 2007 SB evaluations for over 1000 bulls having a minimum of 100 observations for each trait of the pair were 0.20 for service sire traits and 0.03 for sire of cow traits. For the subsets of 132 and 109 active AI bulls, correlations were 0.38 and 0.09. Regressions of sire of cow or service sire evaluations both showed about 0.1% increase in SB/ 1 d increase in GL. As traits of the sire of cow, the relationship between GL and SB was not significant; as service sire traits, there was significance and a 10 d difference in GL could increase SB by 1.4%.