Brito Leonardo F C, Silva Antonio E D F, Unanian Maria M, Dode Margot A N, Barbosa Rogerio T, Kastelic John P
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Sask., S7N 5B4, Canada.
Theriogenology. 2004 Oct 1;62(7):1198-217. doi: 10.1016/j.theriogenology.2004.01.006.
Two experiments were conducted to evaluate sexual development in early- and late-maturing Nelore (Bos indicus) and Canchim (3/8 Bos indicus x 5/8 Bos taurus crossbred) bulls and to determine predictors of sexual precocity, and pubertal and maturity status. In Experiment 1, 12 Nelore bulls where examined from 300 to 900 days of age. Puberty was characterized by an ejaculate containing > or =50 million sperm with > or =10% motile sperm, and maturity by an ejaculate containing > or =70% morphologically normal sperm. In Experiment 2, 28 Canchim bulls where examined from 295 to 488 days of age and puberty was characterized by an ejaculate containing > or =30% motile sperm. In both experiments, bulls were classified as early- or late-maturing based on age at puberty. Early-maturing bulls were younger (P < 0.05) than late-maturing bulls at puberty (527 days versus 673 days in Experiment 1 and 360 days versus 461 days in Experiment 2) and at maturity (660 days versus 768 days in Experiment 1). In general, early-maturing bulls were heavier and had greater scrotal circumference (SC), testes, and testicular vascular cone diameter than late-maturing bulls during the experimental period. Scrotal circumference adjusted for 365 days of age was a good predictor of sexual precocity; minimum yearling SC of 19 and 24 cm for Nelore and Canchim bulls, respectively, had the best predictive values. Early-maturing bulls were lighter and had smaller SC at puberty than late-maturing bulls; therefore, sexual precocity was not related to the attainment of a threshold body weight or testicular size earlier, but to lower thresholds in early-maturing bulls. When predictors of pubertal status were evaluated, SC had the best sensitivity/specificity relationship in Nelore bulls, and high sensitivity and specificity in Canchim bulls. When predictors of sexual maturity were evaluated in Nelore bulls, age, weight, and SC had similar sensitivity, specificity, and predictive values. At puberty, approximately 60% of the sperm present in the ejaculate were morphologically defective. Changes in semen quality after puberty in Nelore bulls were characterized by increased motility and proportion of morphologically normal sperm, with a decrease in the proportion of major sperm defects. In conclusion, early-maturing bulls were more developed in the pre-pubertal period and attained puberty at earlier stages of body and testicular development than late-maturing bulls. Yearling SC could be used to select bulls for sexual precocity and SC was the best predictor of pubertal status. Age, weight, and SC were equally good predictors of sexual maturity in B. indicus bulls.
进行了两项试验，以评估早熟和晚熟的内洛尔牛（印度瘤牛）和坎辛牛（3/8印度瘤牛×5/8黄牛杂交种）公牛的性发育情况，并确定性早熟、青春期和成熟状态的预测指标。在试验1中，对12头内洛尔公牛从300日龄至900日龄进行了检查。青春期的特征是射精量中精子数≥5000万且活动精子比例≥10%，成熟的特征是射精量中形态正常精子比例≥70%。在试验2中，对28头坎辛牛从295日龄至488日龄进行了检查，青春期的特征是射精量中活动精子比例≥30%。在两项试验中，根据青春期年龄将公牛分为早熟或晚熟。早熟公牛在青春期（试验1中为527天对673天，试验2中为360天对461天）和成熟时（试验1中为660天对768天）比晚熟公牛年龄更小（P<0.05）。总体而言，在试验期间，早熟公牛比晚熟公牛体重更重，阴囊周长（SC）、睾丸及睾丸血管圆锥直径更大。校正365日龄后的阴囊周长是性早熟的良好预测指标；内洛尔公牛和坎辛公牛一岁时最小阴囊周长分别为19厘米和24厘米时，预测价值最佳。早熟公牛在青春期时体重更轻，阴囊周长更小；因此，性早熟并非与更早达到阈值体重或睾丸大小有关，而是与早熟公牛更低的阈值有关。当评估青春期状态的预测指标时，阴囊周长在内洛尔公牛中敏感性/特异性关系最佳，在坎辛公牛中敏感性和特异性都很高。当在内洛尔公牛中评估性成熟的预测指标时，年龄、体重和阴囊周长具有相似的敏感性、特异性和预测价值。在青春期时，射精量中约60%的精子形态有缺陷。内洛尔公牛青春期后精液质量的变化特征为活动精子和形态正常精子比例增加，主要精子缺陷比例降低。总之，早熟公牛在青春期前发育更充分，比晚熟公牛在身体和睾丸发育的更早阶段达到青春期。一岁时的阴囊周长可用于挑选性早熟的公牛，阴囊周长是青春期状态的最佳预测指标。年龄、体重和阴囊周长在印度瘤牛公牛中性成熟的预测价值相当。
