Sexual behaviour of rams: male orientation and its endocrine correlates

The components of heterosexual behaviour in rams are reviewed as a basis fo r understanding partner preference behaviour. A small percentage of rams wi ll not mate with oestrous females and if given a choice will display courts hip behaviour towards another ram in preference to a female. Some of the en docrine profiles of these male-oriented rams differ from those of heterosex ual controls. These differences include reduced serum concentrations of tes tosterone, oestradiol and oestrone, reduced capacity to produce testosteron e in vitro, and reduced capacity to aromatize androgens in the preoptic-ant erior hypothalamus of the brain. Our observation that aromatase activity is significantly lower in the preoptic-anterior hypothalamic area of male-ori ented rams than in female-oriented rams may indicate an important neurochem ical Link to sexual behaviour that should be investigated. The defect in st eroid hormone production by the adult testes of the male-oriented ram may r epresent a defect that can be traced to the fetal testes. If this contentio n is correct, partner preference behaviour of rams may also be traceable to fetal development and represent a phenomenon of sexual differentiation.