Foote R H
J Anim Sci. 1978;47 Suppl 2:1-11.
Several inherited conditions associated with testicular defects, abnormal spermatogenesis and morphologically abnormal sperm have been found. These usually are controlled by single gene pairs. A notable exception is testicular size, with heritability in young bulls ranging from .42 to .88. Testicular size directly affects sperm output potential. The major contributor to variation in semen quality is the environment. Environmental effects may be temporary or permanent. Permanent effects occurring during prenatal and prepubertal periods and temporary or permanent factors acting after spermatogenesis is initiated can alter semen quality. Semen quality improves during the first few months after puberty and declines in old age. Malnutrition and the ingestion of toxic materials can have a major effect on testicular development and spermatogenesis, but the reproductive system has considerable regenerative capacity unless the dietary deficiencies are severe and prolonged. Elevated testicular temperatures resulting from incomplete descent of the testes (cryptorchidism), high environmental temperatures or inflammation are detrimental to spermatogenesis in all scrotal mammals. Cold temperatures appear to be innocuous unless actual freezing of tissue occurs. During periods of decreasing daylight semen quality declines in stallions and improves in seasonally breeding sheep. The time required to form and transport sperm in bulls, rams, boars and stallions is about 64, 56, 47 and 59 days. Therefore, a considerable potential lag may exist between a testicular event responsible for a change in semen quality and the time that this change is evident in ejaculated semen. Conditions imposed at the time of semen collection such as frequency of ejaculation, degree of sexual preparation and type of semen collection may influence the quality of semen harvested. Finally, certain semen characteristics are more variable than others and investigators should utilize suitable existing data to design the most effective least-cost experiments.
已发现几种与睾丸缺陷、异常精子发生和形态异常精子相关的遗传性疾病。这些通常由单基因对控制。一个显著的例外是睾丸大小，年轻公牛的遗传力范围为0.42至0.88。睾丸大小直接影响精子输出潜力。精液质量变化的主要因素是环境。环境影响可能是暂时的或永久的。产前和青春期前发生的永久影响以及精子发生开始后起作用的暂时或永久因素都可能改变精液质量。精液质量在青春期后的头几个月会提高，而在老年时会下降。营养不良和摄入有毒物质会对睾丸发育和精子发生产生重大影响，但除非饮食缺乏严重且持续时间长，否则生殖系统具有相当大的再生能力。睾丸未完全下降（隐睾症）、环境温度高或炎症导致的睾丸温度升高对所有阴囊哺乳动物的精子发生都是有害的。除非组织实际结冰，否则低温似乎无害。在日照时间减少期间，种马的精液质量会下降，而季节性繁殖的绵羊的精液质量会提高。公牛、公羊、公猪和种马形成和运输精子所需的时间分别约为64天、56天、47天和59天。因此，导致精液质量变化的睾丸事件与这种变化在射出精液中显现的时间之间可能存在相当大的潜在滞后。精液采集时的条件，如射精频率、性准备程度和精液采集类型，可能会影响采集到的精液质量。最后，某些精液特征比其他特征更易变，研究人员应利用合适的现有数据来设计最有效、成本最低的实验。
