Abstract：
Dimensions of linear type traits facilitate selection of livestock for breeding and rearing. To date, use of linear type traits for selection of breeding bulls is highly concentric to scrotal circumference (SC), with probable overlook to other important traits. Present study reported the importance of various gonadal linear type traits on spermatozoa production, age-related changes in gonadal linear type traits of bulls and predictive ability of these traits on bulls\' reproductive potentials. Among all gonadal traits, testicular density (TD), scrotal volume (SV), paired testicular weight (PWT) and SC were found most important predictor variables in order, which can discriminate between good/poor breeding bulls, that is, produced frozen semen doses (FSD) or not. Dimensions of gonadal traits increased significantly up to 36 months age and thereafter, development became slow and negligible. In contrast, TD decreased by 30%, 51%, 64%, 68% and 71% at 12, 24, 36, 48 and >49 months age, respectively, from its base value at 6 months. Bulls of lower TD (≤0.88 g/cm3) had significantly higher ejaculate volume (+9%), sperm motility, sperm concentration (+100 million/mL) and sperm output (+26%)/ejaculate as compared to bulls of higher TD (>0.88 g/cm3). Discriminant function was developed using TD, SV, PWT and SC to identify bulls of superior reproductive potentials. It was concluded that among the investigated traits, TD was the strongest to discriminate between FSD and Non-FSD bulls. Therefore, our findings suggested that TD could be more potential trait than SC for dairy bulls\' breeding soundness evaluation and assessment of reproductive ability.
摘要：
线性型性状的维度有助于选择牲畜进行育种和饲养。迄今为止,使用线性型性状选择繁殖公牛与阴囊周长（SC）高度同心，可能会忽视其他重要特征。本研究报道了各种性腺线性型性状对精子生产的重要性，公牛性腺线性型性状的年龄相关变化以及这些性状对公牛生殖潜能的预测能力。在所有的性腺性状中,睾丸密度（TD），阴囊容积(SV),配对睾丸重量(PWT)和SC被发现是最重要的预测变量，可以区分好/差的繁殖公牛，也就是说,是否产生冷冻精液剂量（FSD）。直到36个月大，性腺性状的尺寸显着增加，此后，发展变得缓慢和微不足道。相比之下,TD下降了30%，51%,64%,在12、24、36、48和>49月龄时分别为68%和71%，分别,从6个月时的基值开始。较低TD（≤0.88g/cm3）的公牛的射精量显着较高（9％），精子运动性,与TD较高（>0.88g/cm3）的公牛相比，精子浓度（1亿/mL）和精子输出（26％）/射精。使用TD开发了判别函数，SV,PWT和SC可识别具有优越生殖潜力的公牛。结论是，在所调查的性状中，TD在区分FSD和非FSD公牛方面最强。因此,我们的发现表明，TD可能比SC更有潜力的性状用于奶牛繁殖健全性评估和繁殖能力评估。
