Neville W E, Richardson K L, Williams D J, Utley P R
University of Georgia, Tifton 31793-0748.
J Anim Sci. 1989 Nov;67(11):2848-53. doi: 10.2527/jas1989.67112848x.
Angus, Polled Hereford and Santa Gertrudis bulls from ages 1 through 5 and 7 yr were assigned to 26 two-sire breeding groups. Each year, straightbred and crossbred cows of these breeds were allotted at random within breed composition, age of dam and calving date to breeding groups on pasture. Sires within each breeding group or pair were the same age at breeding and were two of the three breeds of sires. Neither calving rate nor the proportion of calves born by one vs the other sire in the two-sire breeding groups was affected by sire age among breeding groups. For a given breed, there was no uniformity among the sires in the proportion of calves they sired in their two-sire breeding groups. The proportion of calves born for the 26 sire pairs averaged .64 vs .36 (SE = 0.4 for either high or low value) for one vs the other sire in a sire pair with no indication that calving rate was affected by unequal proportions of calves by sires within sire pairs. Cows calved significantly earlier in the calving period (b = -.775 +/- .127) as calving rate increased among sire pairs. The number of days from the start of the breeding period to calf birth was affected by differences between sires in sire pairs for 8 of the 26 pairs, but there were no significant differences due to sire pair or breed of sire because of interaction between these two variables.
1至5岁以及7岁的安格斯牛、无角海福特牛和圣格特鲁迪斯公牛被分配到26个双父本繁殖组中。每年，这些品种的纯种和杂交母牛按照品种组成、母牛年龄和产犊日期随机分配到牧场的繁殖组中。每个繁殖组或配对中的公牛在配种时年龄相同，且来自三个公牛品种中的两个。双父本繁殖组中的产犊率以及一头公牛与另一头公牛所产犊牛的比例均不受繁殖组中公牛年龄的影响。对于给定品种，在其双父本繁殖组中，公牛所产犊牛的比例在公牛之间并不一致。在26个公牛配对中，一头公牛与另一头公牛所产犊牛的比例平均为0.64比0.36（高值或低值的标准误均为0.4），没有迹象表明产犊率受到公牛配对中公牛所产犊牛比例不均的影响。随着公牛配对中产犊率的增加，母牛在产犊期显著更早产犊（b = -0.775 ± 0.127）。在26个配对中，有8个配对的公牛配对之间的差异影响了从配种期开始到犊牛出生的天数，但由于这两个变量之间的相互作用，公牛配对或公牛品种没有显著差异。
