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Title:   Author  item
                                            Norman, Hitem
                                            Wright, Janiceitem
                                            Kuhn, Melvinitem
                                            Hubbard, Suzanneitem
                                            Cole, Johnitem
                                            Vanraden, Paul
  Submitted to: Journal of Dairy Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 12/3/2008
                                    Publication  Date: 5/1/2009
                                    Citation: Norman, H.D., Wright, J.R., Kuhn, M.T., Hubbard, S.M., Cole, J.B., Van Raden, P.M. 2009. Genetic and Environmental Factors That Impact Gestation Length in Dairy Cattle. Journal of Dairy Science. 92(5):2259-2269.Interpretive Summary: Information from over 9 million gestations of U.S. dairy cattle was examined. Average gestation length was near 280 d for Holsteins and Jerseys but 288 d for Brown Swiss. Characteristics associated with shorter gestation lengths were young cows, autumn conceptions, multiple births, and heifer calves. Heritability estimates for gestation length of service sire were 33 to 47% and cow sire were 7 to 12%. More accurate prediction of parturition date can help dairy producers manage maternity operations more effectively.
                                Technical Abstract: Genetic and environmental factors that might affect gestation length (GL) were investigated. Data from over 9 million parturitions from 1999 through 2006 for 7 dairy breeds were assembled from lactation, reproduction, and dystocia records from across the United States. Effects examined were year of conception, herd-year of conception, month of conception, age at conception within parity, parturition code (gender and multiple-birth status), cow’s lactation length, cow’s standardized milk yield, service sire, cow sire, and cow. All effects were fixed except for service sire, cow sire, and cow. Mean GL for heifers and cows, respectively, were 277.8 and 279.4 for Holsteins, 278.4 and 280.0 for Jerseys, 279.3 and 281.1 for Milking Shorthorn, 281.6 and 281.7 for Ayrshires, 284.8 and 285.7 d for Guernseys, and 287.2 and 287.5 d for Brown Swiss. Estimated standard deviations of GL were greatly affected by data restrictions but were near 5 to 6 d for most breeds. Year differences in GL were extremely small, but month effects were moderate. GL for Holstein cows was 2.0 d shorter for October conceptions compared with January and February conceptions. GL for Holstein cows with same sex multiple births was 4.7 and 5.6 d shorter than those with single-birth females and males, respectively. Holstein cows with lactations of =250 d had GL 0.8 d longer than cows that were milked for >500 d. Holstein cows with standardized yield of =8,000 kg had GL 0.6 d less than cows with yield of >14,000 kg. Heritability estimates for GL derived from parities 2 to 5 were 33 to 36% for service sire and 7 to 12% for cow sire. Heritability estimates for GL from parity 1 were 46 to 47% and 10 to 12%, respectively. Estimates of genetic correlation between service sire and cow sire for GL were 0.73, 0.79, 0.85, and 0.84 for Holstein heifers, Holstein cows, Jersey heifers and Jersey cows, respectively. More accurate prediction of calving dates could help herd managers meet the management requirements of pregnant animals and administer better health care during the highest risk phases of the animals’ lives.


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