Morrison D G, Williamson W D, Humes P E
J Anim Sci. 1986 Aug;63(2):432-7. doi: 10.2527/jas1986.632432x.
Pelvic measurements, cow weights and cow ages were obtained on 703 Angus- and Hereford-sired cows from five Louisiana Agricultural Experiment Station herds. Cows were either purebred or crossbred, ranging in age from 1 to 14 yr, and sired by 52 Angus and 63 Hereford bulls. All pelvic measurements were obtained via the rectum by the same technician. Paternal half-sib heritability estimates and genetic (rG) and phenotypic (rP) correlations were computed for pelvic height (PH), pelvic width (PW), pelvic area (PA-I; the product of PH X PW), the ratio of PH to PW and cow weight (CW). Pelvic area was also calculated as an ellipse using the formula PA-II = pi (PH/2)(PW/2). Mean PA-I was 298.5 cm2 while PA-II averaged 234.4 cm2. The pooled heritability estimate for PA-I was .68 +/- .34, indicating that pelvic area is a highly heritable trait and should respond to selection. The estimate for PA-II was similar (.66 +/- .34). The heritability of PW was higher than for PH or PA-I. The heritability of CW was .57 +/- .34 and CW was positively correlated (rG2 = .47 and rP = .40) with PA-I. Direct selection for PA-I was estimated to yield a response of 12.2 cm2 in one generation with a correlated response for CW of 12.5 kg. If change in CW was held at zero using a restricted selection index, about 90% as much increase in PA-I was estimated compared with ignoring CW in the index. Therefore, selection for increased pelvic area can be accomplished without causing large increases in cow size. This should aid in reducing calving difficulty.
对来自路易斯安那州农业试验站五个牛群的703头安格斯和赫里福德公牛所生的母牛进行了骨盆测量、母牛体重和年龄测定。母牛为纯种或杂种，年龄从1岁到14岁不等，由52头安格斯公牛和63头赫里福德公牛所生。所有骨盆测量均由同一名技术人员通过直肠进行。计算了骨盆高度（PH）、骨盆宽度（PW）、骨盆面积（PA - I；PH×PW的乘积）、PH与PW的比值以及母牛体重（CW）的父系半同胞遗传力估计值、遗传（rG）和表型（rP）相关性。骨盆面积也用公式PA - II = π(PH/2)(PW/2)计算为椭圆面积。PA - I的平均值为298.5平方厘米，而PA - II的平均值为234.4平方厘米。PA - I的合并遗传力估计值为0.68±0.34，表明骨盆面积是一个高度可遗传的性状，应该对选择有反应。PA - II的估计值相似（0.66±0.34）。PW的遗传力高于PH或PA - I。CW的遗传力为0.57±0.34，且CW与PA - I呈正相关（rG = 0.47，rP = 0.40）。估计对PA - I进行直接选择在一代中可产生12.2平方厘米的反应，对CW的相关反应为12.5千克。如果使用限制选择指数使CW的变化保持为零，与在指数中忽略CW相比，估计PA - I的增加量约为其90%。因此，选择增加骨盆面积可以在不导致母牛体型大幅增加的情况下实现。这应该有助于降低产犊难度。
