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G. Evans and D. T. Armstrong

Summary. Oestrus was synchronized in ewes by (a) withdrawal of an intravaginal progestagen sponge after 12 days or (b) injection of PGF-2α on Day 11 of the oestrous cycle. In addition, ewes were treated with (a) no hormone, (b) 1500 i.u. PMSG 48 h before sponge removal or PG injection, or (c) 24 mg porcine pituitary FSH in multiple injections commencing 48 h before sponge removal or PG injection, in a 2 × 3 factorial design. Ewes were inseminated with 0·2 ml fresh undiluted semen into the neck of the cervix 48 h after sponge removal or PG injection. Normally cyclic ewes were similarly inseminated within 12 h of observed standing oestrus.

At 24 h after insemination one uterine horn and one oviduct were flushed for recovery of spermatozoa and ova. When compared with naturally cyclic ewes, PG synchronization resulted in a marked reduction in the numbers of spermatozoa recovered (P < 0·05), and sponge synchronization led to a small, non-significant, reduction. Within the synchronized ewes, PMSG and FSH resulted in an equivalent superovulatory response, but there was a marked reduction in sperm recovery when compared with unstimulated animals (P < 0·01), with the greatest reduction attributable to PMSG treatment. Spermatozoa were recovered from fewer ewes treated with PMSG than with FSH (P < 0·05). Despite the observed impairment of sperm transport, a high fertilization rate was observed within each group and there were no differences between treatments.

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G. Evans and D. T. Armstrong

Summary. Immature female rats (65–70 g) were injected with 4 i.u. PMSG (control) or superovulated with 8,16,24 or 40 i.u. PMSG and were killed 68–70 h later, shortly after the normally expected time of ovulation. Oocytes were recovered from the oviducts and inseminated in vitro. After 18 h oocytes were counted and classed as degenerate or 1-cell. Mean numbers of oocytes recovered were 8·2, 26·8, 50·7, 38·7 and 38·5 for each dose of PMSG respectively. The 1-cell oocytes were assessed for sperm penetration of the vitellus and pronuclear development and later for development to the 2-cell stage. Fertilization rates at the 1-cell stage were 76·8, 62·9, 53·6, 52·2 and 44·5% for the rats treated with 4, 8, 16, 24 and 40 i.u. respectively (P < 0·001). On average, 91% of fertilized 1-cell oocytes developed to the 2-cell stage and there was no difference between treatments in this respect. Significantly more of the unfertilized oocytes were degenerate in the rats treated with 24 or 40 i.u. PMSG (34·6 and 50·4%) than in those treated with 4, 8 or 16 i.u. (7·0, 13·9, and 7·5%) (P < 0·001).

When rats were killed 63–65 h after PMSG, just before the normally expected time of ovulation, some of the rats treated with 24 and 40 i.u. PMSG had partly ovulated: of the oocytes recovered from the oviducts only 12·3% (24 i.u.) and 26·6% (40 i.u.) were fertilized.

These results demonstrate that proportionately fewer oocytes recovered from superovulated rats are competent to undergo in-vitro fertilization than are oocytes recovered from control rats.

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Barbara K. Evans and G. Burnstock

Summary. Adult virgin female rats were injected daily with low doses (5 or 10 mg/kg) or a high dose (30 mg/kg) of guanethidine for 12 or 8 weeks respectively. 'Short' and 'long' noradrenergic neurones were unaffected by low doses. This contrasts markedly to earlier findings in male rats in which long-term damage of 'short' noradrenergic neurones occurred, and indicates a basic difference between 'short' noradrenergic neurones in male and female rats. Widespread degeneration of both types of neurones followed treatment with high doses and little reinnervation was observed 8 weeks after cessation of treatment. Fertility, pregnancy and litter size were apparently unaffected. Some teratogenic effects were observed in the offspring of female rats treated with guanethidine (10 or 25 mg/kg/day) before and throughout pregnancy. However, these effects had largely disappeared by the time the offspring were 10 weeks old. Since noradrenergic neurones of newborn rats are particularly sensitive to damage by guanethidine it would appear that either very little guanethidine crosses the placental barrier or that noradrenergic neurones are not susceptible during prenatal development to the cytotoxic effects of guanethidine.

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D. T. Armstrong and G. Evans

Summary. Superovulated ewes were inseminated with fresh or frozen semen in a factorial experiment which compared two techniques of artificial insemination; i.e. conventional cervical deposition and intrauterine deposition at laparoscopy. Similar fertilization rates resulted from insemination with fresh semen at cervical (81% of ova from 11/11 ewes) and intrauterine (83% of ova from 10/12 ewes) sites. These results approached those observed in a naturally-mated group (95% of ova from 5/5 ewes). In ewes inseminated with frozen semen, fertilization rate was markedly reduced (P < 0·05) after cervical insemination (11% of ova from 3/11 ewes) and partly restored (P < 0·05) after intrauterine insemination (50% of ova from 8/11 ewes).

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C. A. Evans and T. G. Kennedy

Summary. In hamsters, localized areas of increased uptake of Evans Blue dye, representing the first uterine sign of blastocyst implantation, had an increased concentration of PGE and their appearance on Day 4 was prevented by treatment with indomethacin, an inhibitor of PG synthesis. Indomethacin treatment did not terminate pregnancy: the proportion of animals pregnant on Days 5, 7, 10 and 16 was not affected, although fetal mortality was slightly greater in these animals. Indomethacin treatment caused a decrease in the weights of Evans Blue sites on Day 5 and implantation swellings on Day 10, and the duration of gestation was slightly increased, indicating that implantation had been delayed. This delay did not result from changes of circulating progesterone levels or uterine blood supply. The PG synthesis inhibitors, indomethacin and meclofenamic acid reduced uterine PG concentrations and prevented the appearance of Evans Blue sites in ovariectomized pregnant hamsters treated with progesterone. It is suggested that PGs may be mediators in the uterine Evans Blue response which precedes implantation in the hamster.

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Elizabeth A. Walton, G. Evans and D. T. Armstrong

Summary. Immature female rats (75 g body wt, aged 29 days) were injected with 4 or 40 i.u. PMSG on Day –2 and were killed at intervals between 18:00 h on Day –2 and 09:00 h on Day 1. Control animals (4 i.u.) ovulated between 00:30 and 05:30 h on Day 1 whereas the number of ova recovered from superovulated rats (40 i.u. PMSG) increased slowly between 06:00 h on Day –1 and 24:00 h on Day 0 and markedly between 24:00 on Day 0 and 06:00 on Day 1.

Similarly treated rats were caged overnight on Day 0 with males of proven fertility and killed between 14:00 and 16:00 h on Day 1. A significantly lower percentage of normal 1-cell ova was recovered from the superovulated rats compared to control animals (71·6 and 98·5% and of these 1-cell ova a lower percentage was fertilized (69·7 and 99·1%). In the control group all mated animals had a high proportion of ova fertilized whereas 26% of superovulated rats had none or a very low proportion fertilized. In the control animals there was evidence of sperm penetration and pronucleus fromation; in superovulated rats significantly fewer ova had pronuclei than were penetrated.

These results suggest that reduced fertility of superovulated immature rats is due to complete or partial failure of fertilization in some animals. The extended period during which ovulation occurs may be a contributory factor.

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G. P. Adams, A. C. O. Evans and N. C. Rawlings

Eleven age-matched (±4 days) Hereford heifers were examined by transrectal ultrasonography daily for 18 days beginning 20 weeks (5 months) before puberty (first ovulation) to determine the suitability of the transrectal ultrasound technique for imaging the ovaries of prepubertal heifers and to test the hypothesis that ovarian follicular development occurs in waves in prepubertal heifers. Satisfactory ovarian images were obtained during preliminary ultrasound examinations conducted 4 weeks before the observational period (that is 32 weeks of age), during which a semirigid probe extension was used to allow external manipulation of the intrarectally placed ultrasound transducer. Daily examinations commencing at 36 weeks of age were accomplished by intrarectal placement of the operator's hand and transducer, without complication, in all 11 heifers throughout the observational period. Periodic increases in the number of follicles detected (day effect, P < 0.02) were inversely related to the diameter of the largest follicle (r = −0.3, P < 0.03). Portions of three anovulatory follicular waves were detected in all heifers during the observational period (first and third waves in part and second wave in whole). Individual follicles destined to assume a dominant or subordinate position in a wave were retrospectively identified and monitored beginning at a diameter of 4–5 mm. The interval between the emergence of dominant follicles of successive waves (interwave interval) was 8.0 ± 0.4 days and the interval between successive maxima in the number of follicles per heifer per day was 8.1 ± 0.5 days. The growing phase of the dominant follicles best fit a quadratic curve. The growing phase of the largest subordinate follicles, and the static and regressing phases of dominant and subordinate follicles best fit simple linear expressions. Periodic surges in serum concentrations of FSH (day effect, P < 0.0001), but not of LH (day effect, not significant), were associated with follicular wave dynamics. FSH surges (increase and decrease, respectively, best fit quadratic curves) spanned a mean of 3 days and reached maximum values 0.9 ± 0.3 days before emergence of the wave. Results supported the hypothesis that follicular development occurs in waves in prepubertal heifers. Mechanisms controlling the well-ordered phenomena of wave emergence, follicle selection and follicle regression, similar to those of sexually mature heifers, were present in 36-week-old prepubertal heifers.

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A. C. O. Evans, G. P. Adams and N. C. Rawlings

Changes in the pattern of follicular growth and development, and the associated endocrine changes, were examined in prepubertal heifers approaching their first ovulation. Ten, age-matched (± 3 days), Spring-born Hereford heifers were examined daily by transrectal ultrasonography for 17 days beginning 12 weeks before the first ovulation, and daily from just before the first ovulation until the completion of one normal duration ovulatory cycle. On each day of ultrasound examination, the position and diameter of corpora lutea and follicles ≥ 3 mm in diameter were recorded, and one blood sample was collected. Blood samples were also collected every 15 min, for 12 h, at 20, 12 and 4 weeks before the first ovulation, to assess the pulsatile nature of LH and FSH secretion. The first ovulation occurred at 56.0 ± 1.2 weeks of age, at a body weight of 391.9 ± 12.0 kg. Waves of follicular development, similar to those of adult cows, were seen at all ages, and in all heifers, the first ovulation was followed by an ovulatory cycle of short duration (7.7 ± 0.2 days) and then by a normal duration ovulatory cycle (20.3 ± 0.5 days). The maximum diameter of the dominant, or largest subordinate, follicles did not increase as the first ovulation approached, or during the subsequent ovulatory cycles. Similarly, there were no differences between follicle growth rates (1.4 ± 0.1 mm day−1) or regression rates (1.2 ± 0.1 mm day−1) as the animals matured, and the interwave interval increased up to the first ovulation. Waves of follicular development were associated with peaks in FSH concentrations at 12 weeks before the first ovulation. The short duration, ovulatory cycle was associated with low progesterone concentrations and small corpora lutea (mean maximum values 2.75 ± 0.66 ng ml−1 and 19.9 ± 2.0 mm, respectively), compared with normal cycle durations (10.15 ± 0.58 ng ml−1 and 25.8 ± 0.8 mm). Mean serum oestradiol and LH concentrations and LH pulse frequency increased as the first ovulation approached, but FSH concentrations did not. We conclude that, in heifers before the first ovulation, growth and regression of large follicles occur in a wave-like pattern, with characteristics and associated patterns of gonadotrophin secretion similar to those seen in adult, cyclic animals. Hence, in late prepubertal heifers, factors controlling follicle growth are in place, and there are no changes in these parameters in the three months preceding the first ovulation.

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A. C. O. Evans, G. P. Adams and N. C. Rawling

The aim of this study was to characterize changes in ovarian follicle dynamics in relation to changes in hormone secretion in heifer calves from birth to 8 months of age. The position and diameter of ovarian follicles ≥4 mm in diameter were recorded, the number of ovarian follicles ≥2 mm in diameter counted, and blood samples collected daily for periods of 18 days, starting at 2, 8, 14, 24 and 34 weeks of age in ten heifers. The mean age at first ovulation was 52.8 ± 1.6 weeks. At all ages ovarian follicular development occurred in a wave-like manner, as in mature cattle. The maximum diameter of the dominant and the largest subordinate follicles increased between 2 and 34 weeks of age (P < 0.05); however, the greatest increase occurred between 2 and 8 weeks of age. There was a similar increase in the numbers of small and large ovarian follicles (P < 0.05). The duration of detection of dominant follicles (number of days visible at a diameter of ≥4 mm) also increased between 2 and 34 weeks of age (P < 0.05). The emergence of waves of follicular development was preceded by peaks in plasma FSH concentrations (P < 0.05) at 2 weeks of age but this was less clear at other ages. There was a rise in circulating concentrations of gonadotrophins between 4 and 14 weeks of age. We concluded that in heifer calves as young as 2 weeks of age ovarian follicles grew in a wave-like fashion, similar to those of adult cattle. We speculate that the early rise in gonadotrophin secretion stimulated the increase in numbers of follicles and follicle diameters observed, indicating an early critical step in reproductive development.

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J. P. Foster, Margaret J. Evans and C. H. G. Irvine

Summary. Mares at different stages of the oestrous cycle were given a single intravenous injection of 0·5 mg synthetic Gn-RH.

The mean area of the induced LH peak was significantly less at mid-cycle (Day 10–11) than at any other time. The mean height of the LH peak above preinjection concentration was greater at late oestrus and early cycle (Day 5–6) than at mid-cycle and early oestrus. There were no significant differences in mean FSH responses. The LH:FSH ratio for both height and area of induced peaks was significantly less at mid-cycle than at other times of injection. These results suggest that one releasing hormone could cause the release of both FSH and LH in the normal cyclic mare.