Norman H D, Wright J R, Kuhn M T, Hubbard S M, Cole J B, VanRaden P M
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350, USA.
J Dairy Sci. 2009 May;92(5):2259-69. doi: 10.3168/jds.2007-0982.
Genetic and environmental factors that might affect gestation length (GL) were investigated. Data included information from >11 million parturitions from 1999 through 2006 for 7 US dairy breeds. Effects examined were year, herd-year, month, and age within parity of conception; parturition code (sex and multiple-birth status); lactation length and standardized milk yield of cow; 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 d for Holsteins, 278.4 and 280.0 d for Jerseys, 279.3 and 281.1 d for Milking Shorthorns, 281.6 and 281.7 d 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 generally were approximately 5 to 6 d. Year effects on GL were extremely small, but month effects were moderate. For Holstein cows, GL was 2.0 d shorter for October conceptions than for January and February conceptions; 4.7 and 5.6 d shorter for multiple births of the same sex than for single-birth females and males, respectively; 0.8 d longer for lactations of < or =250 d than for lactations of > or =501 d; and 0.6 d shorter for standardized yield of < or =8,000 kg than for yield of > or =14,001 kg. Estimates for GL heritability from parities 2 to 5 were 33 to 36% for service sire and 7 to 12% for cow sire; corresponding estimates from parity 1 were 46 to 47% and 10 to 12%. Estimates of genetic correlations between effects of service sire and cow sire on GL were 0.70 to 0.85 for Brown Swiss, Holsteins, and Jerseys, which indicates that those traits likely are controlled by many of the same genes and can be used to evaluate each other. More accurate prediction of calving dates can help dairy producers to meet management requirements of pregnant animals and to administer better health care during high-risk phases of animals' lives. However, intentional selection for either shorter or longer GL is not recommended without consideration of its possible effect on other dependent traits (e.g., calving ease and stillbirth).
研究了可能影响妊娠期长度（GL）的遗传和环境因素。数据包括1999年至2006年期间美国7个奶牛品种超过1100万次分娩的信息。研究的影响因素包括年份、牛群 - 年份、月份以及受孕时胎次内的年龄；分娩代码（性别和多胎状况）；奶牛的泌乳期长度和标准化产奶量；配种公牛；母牛的父亲；以及母牛本身。除配种公牛、母牛的父亲和母牛外，所有影响因素均为固定因素。荷斯坦奶牛中，初产母牛和经产母牛的平均妊娠期长度分别为277.8天和279.4天；泽西奶牛分别为278.4天和280.0天；乳用短角牛分别为279.3天和281.1天；艾尔夏牛分别为281.6天和281.7天；根西牛分别为284.8天和285.7天；瑞士褐牛分别为287.2天和287.5天。妊娠期长度的估计标准差受数据限制的影响很大，但一般约为5至6天。年份对妊娠期长度的影响极小，但月份影响适中。对于荷斯坦奶牛，10月份受孕的妊娠期比1月和2月受孕的短2.0天；同性多胎的妊娠期分别比单胎雌性和雄性短4.7天和5.6天；泌乳期小于或等于250天的比泌乳期大于或等于501天的长0.8天；标准化产奶量小于或等于8000千克的比产奶量大于或等于14001千克的短0.6天。第2至5胎次妊娠期长度的遗传力估计值，配种公牛为33%至36%，母牛的父亲为7%至12%；第1胎次的相应估计值为46%至47%和10%至12%。瑞士褐牛、荷斯坦奶牛和泽西奶牛中，配种公牛和母牛的父亲对妊娠期长度影响的遗传相关性估计值为0.70至0.85，这表明这些性状可能受许多相同基因控制，可相互用于评估。更准确地预测产犊日期有助于奶牛养殖户满足怀孕动物的管理要求，并在动物生命的高风险阶段提供更好的医疗护理。然而，在不考虑其对其他相关性状（如产犊难易度和死产）可能影响的情况下，不建议有意选择较短或较长的妊娠期长度。
