Riley D G, Chase C C, Olson T A, Coleman S W, Hammond A C
ARS, USDA, Subtropical Agricultural Research Station, Brooksville, FL 34601, USA.
J Anim Sci. 2004 Jun;82(6):1581-8. doi: 10.2527/2004.8261581x.
The objectives of this study were to assess the risk associated with proportion Brahman inheritance, cow age, dystocia, and birth date weather conditions on calf vigor at birth (n = 3,253) and preweaning mortality (n = 3,631), and to estimate heritabilities for these traits. Calves that had poor vigor at birth and calves that died before weaning were coded 1, and those that had adequate birth vigor or survived to weaning were coded 0. Traits were analyzed using GLM. Year (1951 to 2002), cow age, calfgender, minimum temperature on date of birth (two levels: < 5.6 degrees C; or > 5.6 degrees C), and occurrence of dystocia were main effects in models. The proportion of Brahman inheritance in calves was modeled as a covariate. Males had greater odds of poor birth vigor (odds ratio = 1.44, 95% confidence interval = 1.14 to 1.82). The odds of death before weaning for steers relative to heifers approached significance (P = 0.07; odds ratio 1.41, 95% confidence interval 0.97 to 2.04). Calves born to young (3-yr-old) or very old (13 yr or older) cows had greater (P < 0.05) odds of poor vigor and death before weaning than calves of 5-yr-old cows. Calves with difficult births had 2.59 times greater odds of poor birth vigor (95% confidence interval 1.40 to 4.79) and 12.9 times greater odds of death before weaning (95% confidence interval 8.14 to 20.39) than calves born with no dystocia. Calves born on days with minimum temperatures of 5.6 degrees C or less had greater odds of poor vigor (odds ratio 1.97, 95% confidence interval 1.50 to 2.59) and of death before weaning (odds ratio 1.64, 95% confidence interval 1.27 to 2.13) than did calves born on days with higher minimums. The occurrence of rainfall on date of birth did not influence calf vigor at birth or preweaning mortality (P > 0.85). Purebred Brahman calves had 24.7 times greater odds (95% confidence interval 8.23 to 73.97) of poor vigor than 2/3 Brahman calves. The regression coefficient estimate for fraction of Brahman inheritance approached significance (P = 0.07) for preweaning mortality. Estimates of direct and maternal heritability were 0.09 +/- 0.05 and 0.10 +/- 0.04 for birth vigor, and 0.06 +/- 0.05 and 0.09 +/- 0.04, respectively, for preweaning mortality. Some exploitable genetic variation exists for these traits, but management of other factors may yield more immediate improvement than selection.
本研究的目的是评估婆罗门牛血统比例、母牛年龄、难产以及出生日期的天气状况对出生时犊牛活力（n = 3253）和断奶前死亡率（n = 3631）的相关风险，并估计这些性状的遗传力。出生时活力差的犊牛和断奶前死亡的犊牛编码为1，出生时活力充足或存活至断奶的犊牛编码为0。使用广义线性模型（GLM）分析这些性状。年份（1951年至2002年）、母牛年龄、犊牛性别、出生日期的最低温度（两个水平：<5.6摄氏度；或>5.6摄氏度）以及难产情况是模型中的主要效应。犊牛中婆罗门牛血统的比例作为协变量进行建模。雄性出生时活力差的几率更高（优势比 = 1.44，95%置信区间 = 1.14至1.82）。公牛相对于母牛断奶前死亡的几率接近显著水平（P = 0.07；优势比1.41，95%置信区间0.97至2.04）。由年轻（3岁）或非常老（13岁及以上）母牛所生的犊牛，与5岁母牛所生的犊牛相比，出生时活力差和断奶前死亡的几率更高（P < 0.05）。难产的犊牛出生时活力差的几率比顺产的犊牛高2.59倍（95%置信区间1.40至4.79），断奶前死亡的几率高12.9倍（95%置信区间8.14至20.39）。出生日最低温度为5.6摄氏度或更低的犊牛，与出生日最低温度较高的犊牛相比，出生时活力差的几率更高（优势比1.97，95%置信区间1.50至2.59），断奶前死亡的几率更高（优势比1.64，95%置信区间1.27至2.13）。出生日期的降雨情况对出生时犊牛活力或断奶前死亡率没有影响（P > 0.85）。纯种婆罗门犊牛活力差的几率比2/3婆罗门血统的犊牛高24.7倍（95%置信区间8.23至73.97）。对于断奶前死亡率，婆罗门牛血统比例的回归系数估计接近显著水平（P = 0.07）。出生活力的直接遗传力和母体遗传力估计分别为0.09±0.05和0.10±0.04，断奶前死亡率的直接遗传力和母体遗传力估计分别为0.06±0.05和0.09±0.04。这些性状存在一些可利用的遗传变异，但与选择相比，管理其他因素可能会带来更直接的改善。
