Van Vleck L D, Cundiff L V
Roman L. Hruska U.S. Meat Animal Research Center, Lincoln, NE, USA.
J Anim Sci. 1998 Jun;76(6):1528-34. doi: 10.2527/1998.7661528x.
Weights of males and females can be considered to be correlated traits with different averages and variances. This study attempted to determine whether defining traits as expressed in males or in females would change estimates of breed of sire differences needed to calculate across-breed factors for adjustment of within-breed EPD to across-breed EPD. Records from the US Meat Animal Research Center of progeny of Hereford, Angus, and MARC III composite dams mated to 12 sire breeds that had been used to calculate breed of sire adjustments in 1996 were used. Breeds of sire were Hereford, Angus, Shorthorn, Brahman, Simmental, Limousin, Charolais, Maine-Anjou, Gelbvieh, Pinzgauer, Tarentaise, and Salers. Female and male records for birth (BWT), weaning (WWT), and yearling (YWT) weights were considered to be separate although correlated traits. Heritability estimates for expression as females and males were as follows: .44 and .47 for BWT, .25 and .19 for WWT, and .55 and .49 for YWT. Corresponding genetic correlations between expression in males and females were .85, 1.00, and .92. Phenotypic standard deviations were slightly larger and coefficients of variation slightly smaller for males than for females; the largest differences were for YWT. Breeds ranked similarly for female and male weights; the major exception was Brahman for BWT. Averages of breed of sire contrasts for expression in females and males were almost identical to contrasts from analyses of combined male and female records. Largest differences between averaged and combined breed of sire contrasts were approximately 1 kg for BWT and WWT and approximately 2 kg for YWT. The results show that considering male and female weights as separate traits is not needed in calculation of across-breed adjustment factors from US Meat Animal Research Center records.
雄性和雌性的体重可被视为具有不同均值和方差的相关性状。本研究试图确定将性状定义为雄性或雌性所表达的性状，是否会改变用于计算将品种内预期子代差异（EPD）调整为品种间EPD的品种间因子时，对父系品种差异的估计。使用了美国肉类动物研究中心的记录，这些记录来自赫里福德、安格斯和MARC III复合母本的后代，它们与12个父系品种进行了交配，这些父系品种曾用于计算1996年父系品种的调整。父系品种有赫里福德、安格斯、短角牛、婆罗门牛、西门塔尔牛、利木赞牛、夏洛来牛、缅因-安茹牛、吉尔维牛、平茨高尔牛、塔朗泰斯牛和萨勒斯牛。出生体重（BWT）、断奶体重（WWT）和周岁体重（YWT）的雌性和雄性记录虽为相关性状，但被视为独立的。雌性和雄性表达的遗传力估计如下：BWT分别为0.44和0.47，WWT分别为0.25和0.19，YWT分别为0.55和0.49。雄性和雌性表达之间的相应遗传相关性分别为0.85、1.00和0.92。雄性的表型标准差略大于雌性，变异系数略小于雌性；最大差异出现在YWT上。雌性和雄性体重的品种排名相似；主要例外是BWT的婆罗门牛。雌性和雄性表达的父系品种对比平均值与对雄性和雌性记录合并分析的对比几乎相同。平均父系品种对比与合并父系品种对比之间的最大差异，BWT和WWT约为1千克，YWT约为2千克。结果表明，根据美国肉类动物研究中心的记录计算品种间调整因子时，无需将雄性和雌性体重视为独立性状。
