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Embryonic development will proceed normally in ewes ovariectomized 4 days after ovulation if the animals are treated daily with progesterone (Bindon, 1971). Oestrogens are required for implantation to proceed in rats and mice (Nalbandov, 1971) but this requirement has not been established for sheep. While oestrogens of ovarian origin have been excluded as being necessary for the establishment of ovine pregnancy, it is possible that oestrogen production by the adrenals could supply any requirements at this time (McLaren, 1973).

Adrenalectomized ewes can be mated and become pregnant (Harrison, Heap & Paterson, 1972) provided they are supplied with glucocorticoids and mineralocorticoids. Tilton, Hoffmann, Light & Buchanan (1971) report that adrenalectomy did not not reduce mating activity, fertilization rate or conception rate.

Reliable estimates of oestrogen production by the adrenal have been difficult to achieve because of the very low secretion rates. Baird (1968) found approximately 1 ng oestrone in each of

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J. M. Bedford, R. T. F. Bernard and R. M. Baxter

The Soricidae are generally considered to comprise two subfamilies – Crocidurinae and Soricinae – each of which has distinctive reproductive characteristics. Although Myosorex varius is classified as a crocidurine, the features of its reproductive system call that classification into question. Compared with three other shrew genera, Myosorex exhibited a number of specific features including a relatively prolonged time (about 22 h) for ovulation to be induced by hCG injection and the smallest diameter (75 μm) recorded for any mammal egg. Moreover, the relative testis mass and the number of epididymal spermatozoa were somewhat greater than in some other shrews studied recently. However, many reproductive features in Myosorex have a 'hybrid' character. The glans penis has spines similar to those evident in crocidurines but absent in soricines, yet the accessory sperm storage site, midway along the vas deferens, is similar to that in soricine shrews. The ultrastructure of Myosorex spermatozoa was primarily soricine, despite an unduly large acrosome, which reaches its apogee in the Crocidurinae. Whereas the Fallopian tube displays a crocidurine-type isthmus characterized by deep crypts throughout, the ampulla is richly endowed with ciliated crypts, which in soricines contain spermatozoa. The first polar body persists in the Myosorex ovum, as it does in the soricines Cryptotis and Blarina, but not in the crocidurine Suncus and Crocidura. However, the cumulus oophorus of Myosorex appears largely crocidurine by virtue of its persistent intercellular junctions, long term stability, and the absence of a matrix, lacking only the unique perizonal space that finally characterizes the cumulus of the crocidurines, Suncus and Crocidura. The 'hybrid' character of the reproductive system of Myosorex is more consistent with the proposal that the genus is a survivor of a primitive subfamily – the Crocidosoricinae – from which present day Soricinae and Crocidurinae have arisen.

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J. G. Gong, G. Baxter, T. A. Bramley and R. Webb

Treatment with recombinant bovine somatotrophin (bST) can enhance the development of ovarian antral follicles in cattle. The underlying mechanism was examined further by performing a dose–response study to investigate the effects of bST on peripheral concentrations of somatotrophin, insulin-like growth factor I (IGF-I), insulin, FSH and LH, and ovarian follicle development. Twenty mature heifers were randomly divided into five groups and injected s.c. at 6 h intervals for 7 days with 25% of one of the following daily doses of bST: 0, 3.13, 6.25, 12.5 or 25.0 mg. Ovarian follicular dynamics were monitored by real-time ultrasonography. Blood samples were collected daily during the experiment, and every 15 min for 8 h on days 1 and 5 of bST treatment. Treatment with bST increased (P < 0.01) peripheral concentrations of somatotrophin in a dose-dependent manner. Serum concentrations of both IGF-I and insulin were significantly (P < 0.01) increased in all heifers given 12.5 or 25.0 mg bST per day. Peripheral concentrations of IGF-I and insulin in all animals in the group given 3.13 mg bST and two heifers in the group given 6.25 mg bST were not different from those in the control group, while concentrations in the other two heifers given 6.25 mg bST were significantly (P <0.01) higher. The number of ovarian follicles < 5 mm in diameter was increased (P < 0.05) in response to bST, but only in heifers (n = 10) with significantly increased serum concentrations of IGF-I and insulin. There were no effects of treatment on peripheral concentrations of FSH, LH and progesterone, and on the numbers of follicles > 5 mm in diameter. In conclusion, this study has demonstrated in vivo that the effect of treatment with bST on ovarian follicle development appears to be mediated through an increase in circulating IGF-I or insulin concentrations, rather than via an alteration in the secretion of pituitary gonadotrophins or a direct effect of bST on ovarian follicles.

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R. Webb, G. Baxter, R. D. Preece, R. B. Land and A. J. Springbett

Summary. The patterns of LH and FSH secretion were measured in 4 experimental groups of Finnish Landrace and Scottish Blackface ewes: long-term (18 months) ovariectomized ewes (Group 1), long-term ovariectomized ewes with an oestradiol implant, which has been shown to produce peripheral levels of ∼ 5 pg/ml (Group 2), long-term ovariectomized ewes with an oestradiol implant for 18 months which was subsequently removed (surgery on Day 0) (Group 3) and short-term ovariectomized ewes (surgery on Day 0) (Group 4). LH and FSH concentrations were monitored in all groups at approximately weekly intervals, before and after Day 0. Finnish Landrace ewes in Groups 1, 2 and 3 had significantly higher mean FSH concentrations than did Scottish Blackface ewes (P < 0·01). FSH and LH concentrations increased significantly in Groups 3 and 4, but values in Group 4 were significantly lower (P < 0·01) than those in Group 1 ewes even up to 30 days after ovariectomy. In Group 3, LH concentrations increased to levels similar to those in Group 1. The pattern of LH release was, however, significantly different, with a lower LH pulse frequency (P < 0·05), but higher pulse amplitude (P < 0·05). This difference was maintained at least until 28 days after implant removal.

We suggest that removal of negative feedback by ovariectomy demonstrates an underlying breed difference in the pattern of FSH secretion and that ovarian factors other than oestradiol are also involved in the negative-feedback control of hypothalamic/pituitary gland function. Furthermore, negative-feedback effects can be maintained for long periods, at least 28 days, after ovariectomy or oestradiol implant removal.

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C. S. Haley, G. J. Lee, M. Fordyce, G. Baxter, R. B. Land and R. Webb

Summary. A high and a low response line in sheep were selected on the basis of the mean concentration of LH in 10-week-old Finn–Dorset ram lambs after an i.v. injection of 5 μg GnRH. After 8 male generations the mean LH response of the high line was more than 5-fold that of the low line and the heritability of the selected trait was estimated at 0·44 ± 0·015. Highly significant line differences in mean LH response to GnRH were also found in males at 20 weeks of age and females at 10 and 20 weeks of age and the genetic correlations between the four LH response traits appear to be close to unity. Large line differences in the mean FSH response to GnRH were also found in both males and females at 10 and 20 weeks of age. Selection had little effect on the physical characteristics of lambs. High-response line ewes entering their first breeding season at about 7 months of age showed oestrus earlier in the season and had higher ovulation rates and numbers of lambs born per ewe lambing than did low-response line ewes. In the second breeding season, at about 19 months of age, the only line difference was a higher ovulation rate early in the breeding season in high-line ewes. It is suggested that these changes may be mediated by a more rapid response in high-line ewes to increased GnRH stimulation at puberty or at the beginning of the breeding season.

Keywords: genetic selection; LH release; GnRH; sheep

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KJ Woad, G Baxter, CO Hogg, TA Bramley, R Webb and DG Armstrong

Previous studies have implicated insulin-like growth factors I and II (IGF-I and -II), in the regulation of ovarian function. The present study investigated the localization of mRNA encoding IGF-I and -II and the type 1 IGF receptor using in situ hybridization to determine further the roles of the IGFs within the bovine corpus luteum at precise stages of the oestrous cycle. Luteal expression of mRNA encoding IGF-I and -II and the type 1 IGF receptor was detected throughout the oestrous cycle. The expression of IGF-I mRNAvaried significantly during the oestrous cycle. IGF-I mRNA concentrations were significantly higher on day 15 than on day 10, and IGF-I mRNA in the regressing corpus luteum at 48 h after administration of exogenous prostaglandin was significantly greater than in the early or mid-luteal phase (days 5 and 10). In contrast, there was no significant effect of day of the oestrous cycle on expression of mRNA for IGF-II and the type 1 IGF receptor in the corpus luteum. Expression of IGF-II mRNA was localized to a subset of steroidogenic luteal cells and was also associated with cells of the luteal vasculature. mRNA encoding the type 1 IGF receptor was widely expressed in a pattern indicative of expression in large and small luteal cells. These data demonstrate that the bovine corpus luteum is a site of IGF production and reception throughout the luteal phase. Furthermore, this study highlights the potential of IGF-II in addition to IGF-I in the autocrine and paracrine regulation of luteal function.

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HA Garverick, G Baxter, J Gong, DG Armstrong, BK Campbell, CG Gutierrez and R Webb

A study was conducted to determine the effects of FSH and bovine somatotrophin on the expression of mRNA encoding the gonadotrophin receptors and steroidogenic enzymes in ovarian follicles of cattle rendered hypogonadotrophic by treatment with a GnRH agonist. Hereford x Friesian heifers were allotted into two pretreatment groups: controls (n = 10) and GnRH agonist-treated (n = 20). Ovaries of control cows were removed on day 2 of the first follicular wave after synchronized oestrus. GnRH agonist-treated heifers were given either FSH or no FSH. FSH was infused at 50 microg h(-1) for 48 h. Ovaries in GnRH agonist-treated heifers were removed at the end of exogenous hormone treatment. The control, GnRH agonist and GnRH agonist plus FSH treatment groups were divided further into bovine somatotrophin or no bovine somatotrophin treatments (n = 5 per treatment). Bovine somatotrophin (25 mg day(-1) by s.c. injection) was administered for 3 days. Ovaries were scanned once a day by ultrasonography. Blood samples for hormone measurements were collected three times a day from oestrus until the time of removal of ovaries. Expression of mRNAs for the FSH and LH receptors and cytochrome P450 side-chain cleavage (P450scc), cytochrome P450 17alpha-hydroxylase (P450c17) and cytochrome P450 aromatase (P450arom) enzymes was localized by in situ hybridization and quantified by image analysis. Ovarian follicular growth was arrested at < or = 4.5 mm in diameter in GnRH agonist-treated heifers. There was no effect of bovine somatotrophin on follicular dynamics, gonadotrophin secretion or expression of mRNA for either the gonadotrophin receptors or steroidogenic enzymes. Infusion of FSH to GnRH agonist-treated heifers increased FSH concentrations in serum to the physiological concentrations observed in controls and stimulated growth of follicles to a size similar (5.5-8.0 mm in diameter) to recruited follicles in control cows. FSH induced mRNA expression of P450scc and P450arom in granulosa cells of follicles at a smaller size (< or = 4.5 mm in diameter) than in controls and increased (P < 0.001) expression in larger (> 4.5 mm in diameter) follicles. Expression of mRNAs for P450scc and P450c17 increased (P < 0.001) with increasing follicle size and was higher (P < 0.01) in theca cells of GnRH agonist plus FSH-treated heifers than in the other groups. There were no treatment differences in expression of FSH receptor in granulosa cells or LH receptor in theca cells, but expression of both receptors increased with follicle size. There was no expression of LH receptor in the granulosa cells of cows from any treatment group. In conclusion, FSH treatment in GnRH agonist-treated heifers induced similar changes in follicular growth to those observed during the first follicular wave, but despite similar peak concentrations, prolonged exposure to high FSH induced precocious expression of mRNAs for P450scc and P450arom in granulosa cells from small follicles and markedly upregulated expression of these enzymes in granulosa cells from recruited follicles. The results of this study demonstrate the key role that FSH plays in the induction of follicular growth and differentiation.

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R. Webb, G. Baxter, D. McBride, M. Ritchie and A. J. Springbett

Summary. Three experiments were carried out during seasonal anoestrus in Finnish Landrace and Scottish Blackface ewes, to establish whether the differences between the breeds in ovulation rate are functional during the non-breeding season and are therefore independent of the mechanism controlling ovulation.

In Expt 1, follicles ⩾2 mm in diameter were dissected from the ovaries of both breeds and incubated individually for 2 h to assess their ability to secrete oestradiol and testosterone. In both breeds, follicles producing ⩾500 pg oestrogen/ml/h (oestrogen-active) were readily identifiable from a population producing less (oestrogen-inactive). The number of oestrogen-active follicles in each breed was similar to the number of ovulations near the end of the breeding season. Oestrogen-active follicles also had more luteinizing hormone (LH) receptors and larger diameters than oestrogen-inactive follicles. There were, however, no significant differences between the two follicle types in follicular fluid or in-vitro testosterone concentrations.

In Expt 2, seasonally anoestrous Scottish Blackface ewes were unilaterally ovariectomized; the second ovary was removed 7 days later. Follicles from both ovaries were processed as described for Expt 1; oestrogen-active follicles were categorized according to their ability to produce >500 pg/ml/h. There were twice as many oestrogen-active follicles in the second ovary as in the first ovary; the number of oestrogen-active follicles in the second ovary was also similar to the total number of oestrogen-active follicles in both ovaries of the Scottish Blackface ewes in Expt 1. There were no significant differences between the first and second ovaries for any of the other parameters measured in oestrogen-active follicles. There were no significant changes in peripheral gonadotrophin concentrations measured 24 h after removal of the first ovary.

In Expt 3, seasonally anoestrous ewes of both breeds were challenged with an ovulatory dose of human chorionic gonadotrophin (hCG) (750 iu). There was a significant difference in the mean number of ovulations between the breeds and it was representative for the breed (Finnish Landrace 2·6 ± 0·2; Scottish Blackface 1·6 ± 0·2 mean ovulations per ewe). None of the saline-treated controls ovulated.

The results demonstrated that the mechanism controlling the number of mature, oestrogen-active follicles, and hence ovulation rate, is functional during seasonal anoestrus. This conclusion was confirmed by the observation that compensatory ovarian hypertrophy also occurs during seasonal anoestrus.

Keywords: sheep; follicle; ovulation rate; steroidogenesis; seasonal anoestrus

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A. S. Law, G. Baxter, D. N. Logue, T. O'Shea and R. Webb

Summary. The aim of this study was to investigate the importance of inhibin in the delay in return to oestrus in heifers induced by steroid-stripped bovine follicular fluid (bFF). Oestrous activity was synchronized in 18 Hereford × Friesian heifers with two injections of prostaglandin (PG) 12 days apart. At the time of the second PG injection (time 0), the animals were assigned at random to one of three experimental groups and received i.v. injections of 20 ml saline (controls, n = 6), whole bFF (FF group, n = 6) or bFF in which the bioactive inhibin content had been reduced by >95% by immunoaffinity chromatography (-INH group, n = 6; inhibin content ≈0·8 ml whole bFF) every 8 h for 2 days. In a dose–response study, 2·5 ml whole bFF was insufficient to delay oestrus consistently following a similar synchronization regimen. Blood samples were taken every 8 h, initially before each injection and then subsequently for a further 9 days for hormone analysis. Animals were observed every 8 h throughout the experiment for signs of behavioural oestrus. The ovaries of all animals were examined using real-time ultrasonography about 30 h after the second PG injection.

Treatment failed to suppress peripheral follicle-stimulating hormone (FSH) concentrations, although a significant increase was observed in both treatment groups after cessation of injections. Progesterone concentrations fell immediately after the second PG injection in all animals and remained below minimum detectable concentrations in all treated animals for the remainder of the experiment. In control animals, progesterone rose above minimum detectable concentrations by day 6 and continued to rise until the end of the experiment. Analysis of samples taken from treated animals several days after observed oestrus revealed that all had apparently ovulated. Mean daily luteinizing hormone (LH) concentrations did not differ between treatment groups before ovulation, but after ovulation, mean daily LH was significantly reduced in control animals as progesterone concentrations rose.

Follicular development, as assessed by the mean antral diameter of the largest follicle on a pair of ovaries at ultrasound examination, was significantly suppressed in treated animals compared with controls (P < 0·01) and there was no significant difference (P = 0·397) between the two treatment groups. Control animals displayed oestrus 68 h (± 8 sem) after the second PG injection, but oestrus was delayed in treated animals to 186 h ± 5 (FF group) and 191 h ± 6 (-INH group).

We conclude that the suppression of follicular development and the subsequent delay in return to oestrus associated with bFF treatment of cattle is not due to inhibin. Furthermore, the data suggest that the rebound of FSH concentrations following bFF treatment is similarly due to a factor other than inhibin.

Keywords: inhibin; bovine follicular fluid; FSH; oestradiol; oestrus; cattle

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R. B. Land, B. A. Morris, G. Baxter, Marjorie Fordyce and Janet Forster

Summary. Sera from sheep immunized against oestrone (Group E1), oestradiol (Group E2), androstenedione (Group A) and testosterone (Group T) were given to ewes singly or as a mixture (Group M) of all 4 types as a single intravenous injection at the time of the start of mating. The number of lambs produced, the numbers of eggs shed and the display of oestrus were recorded. The ovulation rates were 1·8 in Group E1, 2·1 in Group E2, 1·6 in Group A, 1·8 in Group T and 2·1 in Group M compared with 1·3 for the controls (P, variation among groups, < 0·001) in the first oestrous cycle. The effect persisted in those animals not conceiving to the first mating—1·3 in Group A, 1·8 in Group E1, 1·9 in Group E2 and 2·0 in Group M compared with 1·3 for the controls; all of the ewes in Group T conceived to mating at a single oestrus. The mean number of lambs born alive per ewe treated was 1·1 for Group A, 1·3 for Group E1, 1·3 for Group E2, 1·5 for Group T, 1·5 for Group M and 1·0 for the controls. The increase in the number of lambs born was due to a higher proportion giving birth to twins (P < 0·01); no ewe gave birth to triplets. High conception rates were recorded for all treatments.