Ford J J, D'Occhio M J
U.S. Department of Agriculture, Clay Center, NE 68933.
J Anim Sci. 1989 Jul;67(7):1816-23. doi: 10.2527/jas1989.6771816x.
Gonadal steroid hormones influence an animal's sexual behavior through two primary means. During development they affect differentiation of the brain (primarily in males), and after puberty, circulating concentrations of steroids influence expression of sexual behaviors. In mammals, sexual behaviors of females are regarded as inherent (independent of steroids secreted by the developing ovary). Males, on the other hand, must undergo active differentiation that is brought about by actions of testicular steroids on the brain during discrete sensitive periods of early development. Sexual differentiation in mammals is referred to as processes of defeminization and masculinization. Defeminization is loss of behavioral traits inherent to females and occurs prenatally in sheep but postnatally in swine. Comparative data are lacking for cattle, but preliminary evidence indicates prenatal defeminization of sexual behaviors. Masculinization is acquisition of behavioral traits characteristic of males. Adult females of all three species show mounting behavior after prolonged treatment with testosterone, and in cattle and swine, there is, as yet, no strong evidence that males undergo masculinization of sexual behaviors. In sheep, limited observations are suggestive of two sensitive periods for masculinization; one prenatally and one postnatally. The earlier concept that differentiation of sexual behaviors in mammals occurs prenatally in species with a long gestation and postnatally in species with a short gestation must now be modified in view of recent findings in swine, in which defeminization occurs postnatally. Further studies will likely identify additional species differences with respect to differentiation of sexual behaviors.
性腺类固醇激素通过两种主要方式影响动物的性行为。在发育过程中，它们影响大脑的分化（主要在雄性动物中），而在青春期后，类固醇的循环浓度影响性行为的表现。在哺乳动物中，雌性的性行为被认为是固有的（独立于发育中的卵巢分泌的类固醇）。另一方面，雄性必须经历由睾丸类固醇在早期发育的离散敏感期对大脑的作用所引起的主动分化。哺乳动物的性别分化被称为去雌性化和雄性化过程。去雌性化是指雌性固有的行为特征丧失，在绵羊中发生在出生前，但在猪中发生在出生后。牛缺乏比较数据，但初步证据表明性行为的产前去雌性化。雄性化是指获得雄性特有的行为特征。所有这三个物种的成年雌性在长期接受睾酮治疗后都会表现出爬跨行为，而在牛和猪中，目前还没有强有力的证据表明雄性会发生性行为的雄性化。在绵羊中，有限的观察结果表明存在两个雄性化敏感期；一个在出生前，一个在出生后。鉴于最近在猪身上的发现，即去雌性化发生在出生后，早期认为哺乳动物性行为分化在妊娠期长的物种中发生在出生前，而在妊娠期短的物种中发生在出生后的概念现在必须加以修正。进一步的研究可能会发现关于性行为分化的更多物种差异。
