Coulter G H, Kozub G C
Research Station, Agriculture Canada, Lethbridge, Alberta.
J Anim Sci. 1989 Jul;67(7):1757-66. doi: 10.2527/jas1989.6771757x.
A study was conducted during the 1982, 1983 and 1984 breeding seasons with 277 crossbred bulls, 1 to 3 yr of age, that were evaluated for physical soundness, testicular development, seminal quality, and both sexual and social behavior immediately before exposure to crossbred cow herds ranging in size from 89 to 329 cows. Crossbred cow herds were exposed to 4 to 24 bulls per breeding group (mean of 14) at a mean female: male ratio of 21.2 +/- .6:1 under extensive range conditions for 31 to 62 d (mean 46.6 d). All resulting calves were blood-typed to determine the number of calves sired by each bull as an estimate of his fertility. The mean number of calves sired by 1- (n = 116), 2- (n = 126) and 3-yr-old (n = 35) bulls was 4.7 +/- .1, 8.2 +/- .1 and 10.5 +/- .1, respectively. A regression model for predicting bull fertility under multiple-sire, range breeding conditions was selected that accounted for 29% of the total variance in fertility. Similar models accounted for a greater proportion of variance in fertility of 1-yr-old (37%) than of 2-yr-old bulls (22%). Due to the large amount of unexplained variation, the model could not predict individual bull fertility precisely. However, this study demonstrated that selection of herd sires with large scrotal circumference, low backfat thickness, low levels of primary sperm defects, and a low number of mounts in combination with a moderate number of services during libido testing would be expected to improve fertility of beef bulls used under extensive range conditions.
在1982年、1983年和1984年繁殖季节，对277头1至3岁的杂交公牛进行了一项研究。在将它们放入数量从89头到329头不等的杂交母牛群之前，对这些公牛的身体健全状况、睾丸发育、精液质量以及性行为和社会行为进行了评估。在粗放的牧场条件下，每个繁殖组将杂交母牛群暴露于4至24头公牛（平均14头），公母比例平均为21.2±0.6:1，持续31至62天（平均46.6天）。对所有产下的犊牛进行血型鉴定，以确定每头公牛所产犊牛的数量，作为其生育能力的一个估计指标。1岁（n = 116）、2岁（n = 126）和3岁（n = 35）公牛所产犊牛的平均数量分别为4.7±0.1、8.2±0.1和10.5±0.1。选择了一个用于预测多公牛、牧场繁殖条件下公牛生育能力的回归模型，该模型解释了生育能力总方差的29%。类似模型对1岁公牛生育能力方差的解释比例（37%）高于2岁公牛（22%）。由于存在大量无法解释的变异，该模型无法精确预测个体公牛的生育能力。然而，这项研究表明，选择阴囊周长较大、背部脂肪厚度较低、初级精子缺陷水平较低、爬跨次数较少且在性欲测试期间配种次数适中的种公牛，有望提高在粗放牧场条件下使用的肉牛公牛的生育能力。
