Summary. Merino ewes were treated with implants which released 300 μg oestradiol-17β per day or 5 mg progesterone per day, or both, for 9 months (Months 1–9), and after an 11-month intermission were treated again for 6 months (Months 20–26). Ewes were run with rams at Months 16, 28 and 40. Fertility was not affected by the first exposure period, but the second exposure to oestradiol reduced the fertility of ewes at both subsequent mating periods. Affected ewes returned to service more frequently (P < 0·01) and were less likely to conceive (P < 0·05). After mating, a normal population of spermatozoa was established in the caudal cervix, but transport through the cervix was impaired in affected ewes and there were fewer spermatozoa (P < 0·01) in the cranial cervix. In affected ewes, the spinnbarkeit of cervical mucus was reduced (P < 0·05), and the histological appearance of the cervix changed, looking like that of the uterus. Treatment with progesterone did not affect fertility, cervical mucus or sperm transport, but diminished the histological abnormalities produced by oestradiol (P < 0·05).
These results show that oestradiol-17β given after puberty can cause the same kind of permanent sexual transdifferentiation that is produced by the oestrogenic isoflavones in ewes with clover disease. The results suggest that this change may require more than a single exposure to oestrogen.
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