Inter-relationships among gonadotrophins, reproductive steroids and inhibin in freemartin ewes

Freemartins are sterile XX/XY chimaeras that occur as a result of placental fusion between male and female fetuses during early pregnancy. Freemartins occur predominantly in cattle, although the prevalence of ovine freemartin ism is increasing. In this study, the reproductive endocrinology of ovine f reemartins was compared with that of normal sheep. Freemartins had signific antly (P < 0.001) higher basal concentrations of LH and FSH than did normal ewes or rams, although the response of LH to GnRH (10 <mu>g) was similar i n freemartins, ewes and rams. Resting concentrations of oestradiol were sim ilar in freemartins and ewes and were increased in both after eCG administr ation. Testosterone concentrations were higher in freemartins than in ewes, but were unresponsive to GnRH or eCG. Administration of 62.5 mg progestero ne or 25 mug oestradiol twice a day for 3 days suppressed LH concentrations to baseline values in freemartins, ewes and rams. In ewes, 500 mug oestrad iol administered twice a day caused preovulatory surges in LH concentration s, but suppressed LH in freemartins to baseline values. Thus, LH secretion can potentially be regulated in freemartins by gonadal steroids. FSH concen trations in freemartins were not suppressed by doses of inhibin that were e ffective in ewes and rams. Therefore, freemartins behave in part like castr ated animals, as they have high basal concentrations of LH and FSH, which c an be stimulated by GnRH and suppressed by gonadal steroids. Conversely, in hibin does not suppress FSH concentrations in freemartins, and freemartins have circulating concentrations of steroids intermediate between those of c astrated and normal animals.