Stimulation of testosterone production by PMSG injection in the ovine male: effect of breed and age and application to males carrying or not carrying the “F” Booroola gene

Characteristics of a direct radioimmunoassay, without extraction, for testosterone in lamb and ram plasma were analysed. After validation, the method was utilised to assay testosterone secretion after PMSG stimulation. Intramuscular injection of PMSG increased testosterone plasma levels from 6 h to 144 h post injection. There was no correlation between the mean levels of testosterone before and after injection. Plasma levels of testosterone in unstimulated animals differed between breeds but after stimulation such differences did not persist. In stimulated animals testosterone plasma levels increased with age during puberty and with dose of PMSG utilised, and were correlated to testis/body weight ratio. PMSG-stimulated secretion of testosterone did not permit identification of male lambs carrying or not carrying the “F” prolificacy gene.