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N. R. Adams

Summary. Ovariectomized ewes, 14 with permanent clover disease infertility (affected ewes) and 14 controls, were injected daily with 40 μg oestradiol benzoate for 12 days, and run with 2 rams fitted with marking crayons. The control ewes were mated sooner (P < 0·05) but both groups became refractory at a similar rate. In a second experiment, 20 similar affected ewes and 19 controls were injected daily with 5 mg testosterone propionate for 31 days and observed daily for 50 min with rams. Affected ewes again were slower to show female behaviour (P < 0·05) but faster (P < 0·05) to show aggression against the rams and other ewes. Over the 31 days, the incidence of female sexual behaviour declined at a similar rate in affected and control ewes. When examined in individual pen tests with oestrous ewes on Day 28, affected ewes showed more male-like courting behaviour than did controls (P < 0·05). The changes in behaviour are too slight to account for the infertility but they do support the hypothesis that phyto-oestrogens can act on the ewe by some of the pathways of sexual differentiation, even after puberty.

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N. R. Adams

Summary. This study examined the effects of prolonged exposure to oestradiol-17β on the morphology of the cervix of the ewe. Merino ewe lambs were implanted subcutaneously with 3 Silastic capsules which released a total of approximately 300 μg oestradiol-17β per day. After exposure for 200 days the uterus was more markedly bicornuate, and the cervix was broader and softer, than in controls. The cervical folds were shorter and contained many stromal cells. The amount of lamina propria under the folds was increased and altered so that it contained tubular glands and more stromal cells. The endocervix thus came to resemble endometrium. This appearance developed within 80 days of exposure, and remained for at least 170 days after implant removal. In a second experiment, mature multiparous Merino ewes were ovariectomized and implanted with 1, 2 or 4 similar oestradiol capsules for 140 days. Similar features developed in these ewes, and the degree of change was almost as great with 1 implant as with 4.

Changes of a similar nature can be produced in other species by oestrogen given during organogenesis but not during adult life. The changes indicate that the ewe has an ability to display a degree of morphogenic response to oestradiol during adult life.

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N. R. Adams

Summary. Ovariectomized ewes, 10 with clover disease infertility and 10 controls, were injected daily for 3 days with 25 μg oestradiol benzoate. At the end of this period, the Spinnbarkeit of cervical mucus and the keratinization of the vaginal epithelium were less in the infertile ewes. It is suggested that the infertility in clover-affected ewes is due to an inability of target organs to give a continued response to the 'priming' action of oestrogen.

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N. R. Adams

Summary. Characteristics of oestrous behaviour were recorded for 14 control ovariectomized ewes treated with 15, 25 or 40 μg oestradiol benzoate (OB), and for 24 ovariectomized ewes, 11 of which were infertile after prolonged intake of oestrogenic clover, which were each treated successively with 0, 10, 15·6 and 24·3 μg OB.

Squatting by the ewe and Flehmen by a ram after sniffing the ewe were not associated with oestrogen treatment. 'Looking over the shoulder' was a sign exhibited by most ewes treated with 10 μg OB, but not by ewes that did not receive oestrogen. There were no differences between clover-affected and control ewes for these responses.

Active soliciting by the ewe, standing for mounting, and being mounted by the ram, were behavioural responses closely associated with doses of OB greater than 15 μg. Tail fanning and kicking by the ewe were less closely associated with higher doses of OB. All of these responses were slightly but significantly diminished in clover-affected ewes, either in incidence, duration, or by a later time to onset. The results support the hypothesis that prolonged exposure to plant oestrogens causes persistent desensitization of the hypothalamus of the ewe to oestrogen.

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N. R. Adams and M. R. Sanders

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.

Keywords: oestradiol; infertility; ewes; transdifferentiation; cervix

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N. R. Adams and B. Y. Tang

Summary. The amount of cervical mucus recovered from control ovariectomized ewes increased with increasing doses of oestradiol benzoate (OB), while the maximum Spinnbarkeit of mucus occurred at an intermediate dose of OB. Neither the amount nor the Spinnbarkeit of mucus varied with the dose of OB in ewes with permanent infertility caused by grazing oestrogenic pasture (clover-affected ewes). Furthermore, the increase in Spinnbarkeit of cervical mucus seen in normal ewes treated over a 3-day period with OB or with implants containing oestradiol did not occur in affected ewes. In control ewes treated repeatedly with OB, production of mucus declined within 5 days, but no change in secretion was detectable in clover-affected ewes. Therefore, neither the amount nor the duration of oestrogenic stimulation affected the cervical mucus in ewes with clover disease. Affected ewes produced more mucus than did controls in the absence of oestrogenic stimulation. It is concluded that the relatively normal volume of mucus in affected ewes treated with OB results largely from autonomous production. The Spinnbarkeit does not increase in these ewes because the ability of the cervix to respond to oestrogen is impaired.

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N. R. Adams and B. Y. Tang

Summary. After 10 days pretreatment with 10 mg progesterone daily, ovariectomized ewes were injected i.m. with 12·5, 25, 50 or 100 μg oestradiol benzoate (OB) and cervical mucus was collected 16, 24, 32, 40 and 48 h later (Exp. 1), or were injected with 12μ5, 40 or 100 μg OB daily, and the mucus examined, for 9 days (Exp. 2). The Spinnbarkeit was affected by the dose of OB over 9 days, but at all doses it increased over the first 3 days of treatment (Exp. 2). The wet weight of the mucus, the amount and proportion of water, and therefore the degree of arborization, increased with the dose of OB but decreased after 3 days in Exp. 2. The amount of dry matter, protein or carbohydrate did not have any clear relationship to dose or duration of OB treatment.

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N. R. Adams, C. M. Oldham, and R. A. Heydon

Summary. Ewes which had been exposed to oestrogenic clover for 3 years showed an elevated ovulation rate but no difference in numbers of primordial follicles compared with normal ewes.

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N. R. Adams, S. Atkinson, and M. R. Sanders

Summary. In a series of 5 experiments, ewes were treated with implants releasing oestradiol-17β and the effects on ovulation rate were observed. Large doses of oestradiol-17β (> 20 μg/day) produced anovulation while smaller amounts only reduced the proportion of twin ovulations. Amounts of exogenous oestradiol comparable to ovarian production rate in the luteal phase (< 1 μg/day) produced a significant (P < 0·01) suppression in ovulation rate. Treatment during the follicular phase of the oestrous cycle was most effective, but treatment during the luteal phase alone also appeared to suppress ovulation rate. Furthermore, in 2 of 3 experiments ewes treated with low amounts of oestradiol during the first half of the luteal phase were less likely to have multiple ovulations at the subsequent oestrous period. The results support the hypothesis that oestrogen is involved in the physiological control of ovulation rate in the ewe, but this action is probably not restricted to the assertion of dominance by a maturing follicle during the follicular phase.

Keywords: oestrogen; ovulation rate; sheep

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S. Atkinson, N. R. Adams, and G. B. Martin

Summary. In two experiments, mature Merino ewes were fitted with subcutaneous implants containing oestradiol-17β or empty implants (control). Peripheral concentrations of LH and FSH were measured during luteal and follicular phases, which were synchronized by means of intravaginal progestagen-impregnated sponges. The ovulation rates of the ewes were determined by laparoscopy, 1 week after luteolysis. In Exp. 1, small implants (3 mm) decreased the LH pulse frequency before luteolysis. In the ewes with oestradiol implants, the amplitude of the preovulatory surge of LH was reduced and the onsets of the LH and FSH surges were delayed. There was no effect of oestradiol on LH baseline, LH pulse amplitude or in the concentration of FSH during the luteal or follicular phases. In Exp. 2, larger implants (10 mm) were inserted for the luteal, follicular, or luteal + follicular phases. The control ewes had empty implants. In the ewes with oestradiol implants, LH pulse frequencies were decreased during the luteal phase. This decrease persisted throughout the follicular phase, even though the oestradiol implants had been removed. There were no differences in the other measures of LH or FSH in the luteal or follicular phases. Ovulation rates were not affected by oestradiol treatment in either experiment, indicating that the regulation of LH pulse frequency is not a critical factor in the determination of ovulation rate in ewes. This was supported by retrospective analysis of the gonadotrophin profiles of single and twin-ovulating ewes, in which all measures of LH were similar between the two groups. However, twin-bearing ewes had slightly higher circulating concentrations of FSH during the luteal phase. As the difference in FSH was not large (13%), and it disappeared after luteolysis, it is difficult to postulate that FSH plays a major role in the final selection of the preovulatory follicle(s) in the ewe.

Keywords: ovulation rate; LH; FSH; oestradiol; sheep