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The volume of cervical mucus produced in the ewe appears to be controlled by the circulating levels of oestrogen (Vickery & Bennett, 1968), and is greatest during pro-oestrus and oestrus (Grant, 1934). The volume produced is of the order of 20 ml (Restall, 1967) and in spayed ewes is a linear function of the quantity of exogenous oestrogen (Lindsay & Francis, 1968).

It seems, therefore, that the disturbance in the pattern of oestrogen production in the ewe in which oestrus is controlled with progestagen-impregnated sponges (Smith & Robinson, 1970) may be reflected in the production of cervical mucus and that this could account for the changed pattern of transport of spermatozoa following progestagen treatment (Quinlivan & Robinson, 1967, 1969).

Forty-five Merino ewes, aged 5 years, randomized into three progestagen-dose-level groups of fifteen ewes

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The reasons for low fertility in a flock of inbred sheep were investigated. Of a total of forty-one inbred ewes run with tested rams at normal mating time, sixteen (39%) were unlikely to have carried a lamb to term. Causes included non-ovulation (six ewes), non-cleavage or abnormal cleavage of ova (four ewes) and non-viability of early implanted embryos (six ewes). Out of twenty-six non-inbred half-sibs of similar ages only one potentially infertile ewe was found (non-ovulation).

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G. W. Asher and J. F. Smith

Summary. Twenty non-lactating fallow does were each treated with an intravaginal progesterone device (CIDR) for 14 days followed by an i.m. injection of 500 i.u. PMSG, 3–4 weeks before the expected start of the natural rut. An additional 7 does received no treatments and were used as controls. Induced oestrus was observed for 19 (95%) of the treated does, the onset occurring between 48 and 76 h after CIDR removal/PMSG administration. Laparoscopic examination 12 days after CIDR removal revealed ovulation rates ranging from 1 to 4 in treated does. Non-ovulating luteinized follicles were also a feature of PMSG treatment and there was a significant inverse relationship between ovulation rate and numbers of luteinized follicles. Only 3 (14·3%) of the treated does conceived at or near the induced oestrus, the remainder returning to oestrus 21–27 days later. Mid-cycle progesterone concentrations were positively related to ovulation rate. All control does showed evidence of a recent single ovulation at laparoscopy, although first oestrus did not occur until 7–15 days later, indicating the occurrence of silent ovulations before the natural breeding season.

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R. J. Fairclough, J. F. Smith and A. J. Peterson

Previous studies have suggested that the biological activity of steroid hormones can be neutralized by antibodies raised against steroid–protein hormones. Active (Ferin, Zimmering, Lieberman & Vande Wiele, 1968) or passive (Scaramuzzi, 1975) immunization procedures have been reported. The latter method is particularly useful when studying the physiological role of hormones in the oestrous cycle when hormonal changes occur during a relatively short interval.

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J. F. Smith, R. J. Fairclough and A. J. Peterson

Summary. Plasma concentrations of progesterone and Provera were measured daily in 3 cows during 21 days of treatment with Provera-impregnated intravaginal sponges. Plasma concentrations of oestradiol-17β and 13,14-dihydro-15-keto-prostaglandin F (PGFM) were measured hourly from 5 h before until 62 h after sponge removal. The profile of progesterone concentrations indicated that luteolysis occurred at the expected time (Days 19 to 23 of the cycle), even though plasma Provera concentrations were 150–250 pg/ml. The occurrence of peaks of PGFM after sponge withdrawal suggests that PGF-2α release is stimulated by falling levels of progestagen.

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A. J. Peterson, R. J. Fairclough and J. F. Smith

Summary. Androstenedione and testosterone were measured by radioimmunoassay after chromatography on micro-columns of Lipidex-5000 in jugular plasma samples taken every 2–3 h at the time of luteolysis and oestrus in 3 dairy cows. The concentrations of androstenedione and testosterone varied between 5 and 60 pg/ml and 5 and 80 pg/ml respectively and no consistent pattern in the fluctuations of either steroid was observed.

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R. J. Fairclough, J. F. Smith and L. T. McGowan

Summary. Three cows and 2 sheep were passively immunized against prostaglandin (PG) F on Day 16 and Days 13–15 of the oestrous cycle respectively. The PGF antiplasma was raised in ovariectomized ewes against a PGF-2α–bovine serum albumin complex and showed 100%, 12·5%, 0·3%, <0·05% and <0·01% cross-reactivity with PGF-2α, PGE-2, PGA-2, PGB-2 and arachidonic acid, respectively. Control animals were given an equivalent amount of ovariectomized ewe plasma. In all passively immunized animals there was evidence of a persistent corpus luteum as indicated by plasma progesterone concentrations and the failure of the animals to return to oestrus until at least 29 days after treatment. These data are consistent with previous proposals that PGF-2α is the uterine luteolytic factor in sheep and cattle.

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J. F. Smith, M. E. di Menna and L. T. McGowan

Summary. The reproductive performance of Coopworth ewes after administration of zearalenone was determined in two trials. In Trial 1, zearalenone was administered to groups of 33 ewes at rates of 0, 1·5, 3·0, 6·0, 12·0 and 24·0 mg/ewe/day for 10 days, starting on Day 7 of the oestrous cycle before mating. There was a linear decline (P < 0·001) in ovulation rate with dose of zearalenone; also cycle length decreased and duration of oestrus increased with increasing dose levels. Reductions in the incidence of ovulation and in fertilization were seen only at doses of 12 and 24 mg. In Trial 2, groups of 50 ewes were given the same range of doses of zearalenone for 10 days, starting 5 days after mating to entire rams. There was no effect of zearalenone treatment after mating on pregnancy rate or embryonic loss. These results indicate that the effects of zearalenone, administered orally, on ewe reproduction, at the dose levels examined, were restricted to ewes exposed before mating. Intakes of zearalenone of 3 mg/ewe/day or more during this period would be reflected as depressed ovulation rates and lower lambing percentages.

Keywords: zearalenone; ewes; ovulation; oestrus; fertility

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J. B. Phogat, R. F. Smith and H. Dobson

This study examined the effect of transport on GnRH self-priming in vivo as well as the consequential effects on the oestradiol-induced LH surge. The follicular phases of ewes (eight per group) were synchronized with progestin sponges, and 50 μg oestradiol benzoate was injected 24 h (time zero) after sponge removal to improve precision in the timing of the LH surge. Beginning 8 h after oestradiol, saline or GnRH (500 ng, i.v.) was given at 2 h intervals with or without 8 h transport beginning 0.5 h before the first GnRH injection (late transport) and effects were compared with those observed during early transport, that is, starting 2.5 h before the first GnRH injection. In all ewes, GnRH alone induced a maximum LH response of 1.9 ± 0.4 ng ml−1 after the first challenge. The response was enhanced (P < 0.01) after the second and third GnRH injections (7.4 ± 1.4 ng ml−1 and 7.6 ± 1.7 ng ml−1, respectively). This self-priming effect after the second GnRH was reduced by late transport (7.4 ± 1.4 versus 4.2 ± 0.8 ng ml−1; P < 0.05) but not early transport, that is, transport initiated closer to the time of GnRH administration had greater suppressive effects on LH secretion. Throughout transport, spontaneous LH pulse frequency was lower in treated than it was in control ewes (2.38 ± 0.53 versus 4.50 ± 0.53 pulses per 8 h; P < 0.01), with marked effects in the first 4 h of transport (1.0 ± 0.19 versus 2.63 ± 0.38 pulses per 4 h; P < 0.02). Spontaneous pulse amplitude also tended to decrease during transport (0.13 ± 0.02 versus 0.20 ± 0.03 ng ml−1; P = 0.07). When LH turnover was stimulated by exogenous GnRH, the onset of the LH surge was delayed (controls: 20.5 ± 2.0 h versus GnRH alone: 25.3 ± 1.5 h; P < 0.05) and the duration was reduced (8.5 ± 0.9 versus 6.5 ± 0.4 h; P < 0.05). Transport tended to delay the LH surge in saline-treated ewes (20.5 ± 2.0 versus 22.9 ± 1.9 h; P = 0.08), with a further delay imposed by late transport plus GnRH (27.5 ± 1.6 h; P < 0.05) but not by early transport plus GnRH (27.8 ± 2.5 versus 26.4 ± 2.4 h; P > 0.05), that is, effects mediated by increasing LH turnover were only manifest if transport occurred near the LH surge, when there was insufficient time to replenish stores of releasable LH. In all transported ewes, plasma cortisol increased from 4.5 ± 1.0 ng ml−1 to 29.2 ± 5.5 ng ml−1 (P < 0.001) within 15 min of the start of transport and was significantly lower (P < 0.01) by 6.5 h. Plasma progesterone also increased from 0.30 ± 0.04 to 0.38 ± 0.04 ng ml−1 (P < 0.05). In conclusion, transport affected the oestradiol-induced LH surge by causing a 50% reduction in the self-priming effect of exogenous GnRH, but hypothalamic effects were also revealed by a two-fold decrease in spontaneous LH pulse frequency in saline-treated ewes.

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Dianne Moore Smith, J. P. P. Tyler and G. F. Erickson

Summary. Rabbit oocytes from large (1–1·5 mm diam.), medium (0·5 mm) and small (0·15–0·25 mm) antral follicles were cultured in five chemically defined media. In all media, oocytes from large antral follicles showed the highest incidence of meiotic activity followed by those from follicles of medium size. Most oocytes from small follicles did not resume meiosis in culture. The addition of glutamine to a standard medium for ovum culture significantly improved maturation of oocytes from medium-sized follicles but did not affect those from large or small follicles. When polyvinylpyrrolidone was substituted for bovine serum albumin, maturation of oocytes from large and medium-sized follicles was reduced. Progesterone at a concentration of 10 μM did not affect maturation, but 100 μM-progesterone blocked germinal vesicle breakdown in oocytes from medium-sized follicles and reduced both germinal vesicle breakdown and polar body formation in oocytes from large follicles. This effect was reversible.