Skip to main content
ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #138387
Title: RELATIONSHIP OF SERUM TESTOSTERONE CONCENTRATIONS TO MATE PREFERENCES IN RAMS

Author
item ROSELLI, CHARLES - OREGON HEALTH SCI. UNIV.
item STORMSHAK, FRED - OREGON STATE UNIV.
item Stellflug, John
item RESKO, JOHN - OREGON HEALTH SCI. UNIV.

Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2002
Publication Date: 7/1/2002
Citation: Biology of Reproduction. 2002. v. 67. p. 263-268.

Interpretive Summary: Individual variations exist in sexual performance of rams as well as in the object of their sexual attraction . Most adult rams readily court, mount, and ejaculate when exposed to females in estrus. However, intensity of exhibited sexual behavior can range from asexuality to high libido. Moreover, whereas most rams express a sexual partner preference for females and are classified as female-oriented rams, a small percentage of rams express a sexual partner preference for males and are classified as male-oriented rams. Testosterone and its component androgenic and estrogenic signaling pathways in the nervous system are critical for expression of masculine sexual behaviors in vertebrates. Therefore, this study examined testosterone concentrations in rams that were classified according to their sexual behavior and partner preference as either female-oriented, male-oriented, or asexual. Testosterone concentrations were measured under three separate conditions: in conscious rams during the nonbreeding season (June) and breeding season (November), and in anesthetized rams during the breeding season. Basal testosterone concentrations in conscious rams were not different among the three groups in either season. However, when rams were anesthetized, mean systemic concentrations of testosterone in female-oriented rams were greater than in asexual, but not in male-oriented rams, whereas testosterone concentrations were not different between male-oriented and asexual rams. Concentrations of testosterone in the spermatic vein of female oreinted rams were greater than in male-oriented and asexual rams. Serum LH concentrations were not different. Cortisol was higher in anesthetized male-oriented and asexual than in female-oriented rams. In summary, this study, together with our previously published research, demonstrate that circulating concentrations of testosterone are related to sexual orientation in anesthetized rams, but not in conscious rams. These results make it seem highly unlikely that differences in basal androgen concentrations in adult rams are responsible for expression of male-oriented preferences or low libido. Instead, because the endocrine response to anesthesia is most likely coordinated through the central nervous system, we hypothesize that neural substrates mediating these responses differ among female-oriented, male-oriented and asexual rams.

Technical Abstract: This study examined systemic testosterone concentrations in rams that were classified according to their sexual behavior and partner preference as either female-oriented (FOR), male-oriented (MOR), or asexual (NOR). For this purpose, we measured testosterone concentrations under three separate conditions: in conscious rams during the nonbreeding season (June) and breeding season (November), and in anesthetized rams during the breeding season. Basal testosterone concentrations in conscious rams were not different among the three groups ( P < 0.05) in either season. However, when rams were anesthetized, mean systemic concentrations of testosterone in FORs (mean +/- SEM, 13.9 +/- 7.4 ng/ml serum) were greater ( P < 0.05) than in NORs (0.9 +/- 0.1 ng/ml), but not in MORs (2.2 +/- 6.2 ng/ml), whereas testosterone concentrations were not different between MORs and NORs ( P < 0.05). Concentrations of testosterone in the spermatic vein of FORs (127 +/- 66 ng/ml) were greater ( P < 0.05) than in MORs (41 +/- 10 ng/ml) and NORs (19 +/-7 ng/ml). Serum LH concentrations were not different. Cortisol was higher ( P < 0.05) in anesthetized MORs (25.1 +/- 4.2 ng/ml) and NORs (27.2 +/- 4.4 ng/ml) than in FORs (10.9 +/- 1.8 ng/ml). These results demonstrate that circulating testosterone concentrations are related to sexual behavior only when rams are bled under anesthesia. Thus, differences in basal androgen concentrations in adulthood cannot be responsible for expression of male-oriented preferences or low libido in sheep. Instead, functional differences must exist between the brains of rams that differ in sexual preference expression.