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Local heating of the scrotal contents of rams to approximately 40°C for 1½ to 2hr causes a sharp increase in the proportion of morphologically abnormal spermatozoa in the ejaculate 14 to 16 days later (Braden & Mattner, 1970). This period of delay approximates to the epididymal passage time for ram spermatozoa (Dawson, 1958; Amir & Ortavant, 1968), and has been cited as evidence that spermatozoa undergoing epididymal passage at the time of heating are resistant to damage (Braden & Mattner, 1970).

In the present study, observations were made of the changes in the fine structure of ejaculated ram spermatozoa after mild scrotal heating.

Four mature Saxon Merino rams which produced good quality semen were restrained in metabolism cages. The scrota of three of them (Rams A, B and C) were immersed for

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S. Atkinson and P. Williamson

Summary. Southdown ewes in mid-seasonal anoestrus were exposed to rams for 0 h (control group), 2 h, 24 h, 40 h, 3 days, 10 days or 20 days. Serial blood samples were then taken to determine LH and FSH levels. Ewes with >24 h ram exposure were ovariectomized immediately after bleeding, and all follicles >1 mm diameter were dissected from the ovaries and measured. LH basal concentrations and pulse frequency increased significantly within 2 h of ram introduction, but by 24 h fell, and then remained low. FSH concentrations fell within 2 h of ram introduction and remained low. Control group ewes (isolated) had no follicles >4 mm diameter, whereas all ewes exposed to rams had large follicles, with CL or preovulatory follicles present at 40 h after ram introduction. Ram introduction was also associated with follicle recruitment (antrum formation to <2 mm). Follicular recruitment and development to the large follicle stage therefore occurred during a period of low plasma gonadotrophin levels and suppressed LH pulsing.

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P. Williamson, N. J. Gales, and S. Lister

Summary. Real-time ultrasonography was used to detect pregnancy in 4 captive bottlenose dolphins. Pregnancy was readily confirmed from around the 4th month of gestation by imaging fetal fluids and fetal movement. Periodic examination permitted monitoring of the viability of the fetuses by observation of their heart beat and movement, and serial measurements of skull diameter (occipito-frontal axis) and thoracic diameter was possible. A growth curve for these measurements was plotted.

Keywords: bottlenose dolphin; pregnancy diagnosis; real time ultrasound; fetal growth rate; reproduction

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P. Williamson, T. P. Fletcher, and M. B. Renfree

Summary. Testicular growth and maturation of the hypothalamic–pituitary–testicular axis were assessed in male tammars from 12 to 25 months of age to establish the time of sexual maturity. The testicular dimensions and body weights of 20 male tammars, ∼12 months of age at the beginning of the study, were measured monthly for 1 year. Groups of 3 animals were castrated at 13, 19 and 25 months of age and their testes sectioned for histological examination. Testicular volume increased between 12 and 24 months of age and was highly correlated with body weight (r = 0·91). In the 13-month group the seminiferous tubules were closed with few mitotic figures. Spermatogenesis had begun in 2 of the 19-month animals. All stages of spermatogenesis were present in the other 19-month male, and in all of the 25-month males.

Basal FSH concentrations increased with the age of the animal (21·0 ± 32·48, 94·40 ± 55·18 and 193·05 ± 40·21 ng/ml (mean ± s.d.) at 19, 20 and 25 months respectively) while basal LH concentrations were similar at 20 months and 25 months (0·43 ± 0·18 and 0·58 ± 0·25 ng/ml respectively). Basal testosterone concentrations were also similar 0·11 ± 0·04, 0·35 ± 0·16 and 0·22 ± 0·10 ng/ml in 13-, 19- and 25-month-old animals.

LHRH injection in tammars at 13, 19 and 25 months of age induced release of both LH and testosterone 10#x2013;30 min after injection. The hormone concentrations increased in both magnitude and duration with increasing age. At 13, 19 and 25 months, peak testosterone values of 1·13 ± 0·27, 1·90 ± 0·45 and 6·58 ± 0·91 ng/ml (mean ± s.d.), respectively, were measured by 90–120 min after injection and peak LH values at 13, 19, 20 and 25 months of age were 2·46 ± 0·82, 8·31 ± 2·02, 9·0 ± 2·18 and 7·86 ± 1·41 ng/ml, respectively, when measured 30 min after injection. By contrast, LHRH injection did not increase FSH concentration at 20 or 25 months of age above the basal concentration.

Taken together, the morphological and endocrinological data show that puberty in male tammars begins around 19 months and is complete by 25 months of age.

Keywords: testis, testosterone; LH; FSH; LHRH; spermatogenesis; marsupial; puberty

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F. P. Sumbung, P. Williamson, and R. S. Carson

Summary. Prepubertal ewe lambs were treated with FSH after progesterone priming for 12 days (Group P), monensin supplementation for 14 days (Group M) or a standard diet (Group C). Serial blood samples were taken for LH and progesterone assay, and ovariectomy was performed on half of each group 38–52 h after start of treatment to assess ovarian function, follicular steroid production in vitro and the concentration of gonadotrophin binding sites in follicles. The remaining ewe lambs were ovariectomized 8 days after FSH treatment to determine whether functional corpora lutea were present.

FSH treatment was followed by a preovulatory LH surge which occurred significantly later (P < 0·05) and was better synchronized in ewes in Groups P and M than in those in Group C. At 13–15 h after the LH surge significantly more large follicles were present on ovaries from Group P and M ewes than in Group C. Follicles > 5 mm diameter from ewes in Groups P and M produced significantly less oestrogen and testosterone and more dihydrotestosterone, and had significantly more hCG binding sites, than did similar-sized follicles from Group C animals. Ovariectomy on Day 8 after the completion of FSH treatment showed that ewes in Groups P and M had significantly greater numbers of functional corpora lutea.

These results indicate that, in prepubertal ewes, progesterone priming and monensin supplementation may delay the preovulatory LH surge, allowing follicles developing after FSH treatment more time to mature before ovulation. This may result in better luteinization of ruptured follicles in these ewes, with the formation of functional corpora lutea.

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S. Atkinson, P. Williamson, C. L. Kang, and R. S. Carson

Summary. The introduction of rams to a group of previously isolated anoestrous ewes has been shown to stimulate ovarian follicular development and ovulation. The present experiment was carried out to determine the ability of follicles arising from this ram stimulus to produce steroids and bind hCG. Seasonally anoestrous Southdown ewes were exposed to rams for 24 h, 40 h, 3 days, 10 days or 20 days before ovariectomy. Steroid production and the concentration of hCG binding sites in follicles dissected from the ovaries were measured in vitro. The presence of a ram caused ovulation and enhanced oestradiol production by follicles, but had little effect on total androgen production or the number of hCG binding sites present in the follicles when compared to follicles from anoestrous ewes. The oestradiol concentrations in large follicles were not as high as in preovulatory follicles from cyclic ewes reported in other studies. Follicles continued to develop through the ram contact period and when incubated after 40 h and 10 days of ram contact produced high levels of progesterone, indicating partial luteinization, although the corpora lutea (CL) resulting from the induced ovulations regressed prematurely. We suggest that the lack of hCG binding sites in ram-induced follicles may be the cause of poor luteinization and suboptimal development of luteal tissue after induced ovulation in ewes during seasonal anoestrus.

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N. J. Gales, P. Williamson, L. V. Higgins, M. A. Blackberry, and I. James

Concentrations of circulating progesterone and oestradiol were measured in 96 free-ranging, female Australian sea lions Neophoca cinerea from Kangaroo Island, South Australia. There was a marked increase in the concentrations of both hormones (progesterone from approximately 12 ng ml−1 to approximately 24 ng ml−1; oestradiol from approximately 1.5 pg ml−1 to approximately 14 pg ml−1) about 3.5 months after the probable date of mating, reaching peak values in the 5 months after parturition. Progesterone concentrations remained at peak concentrations for about 2 months, decreasing at approximately 8 months to concentrations approximating those of the first 3 months after parturition. Oestradiol concentrations decreased, after reaching a peak, to 3–4 pg ml−1 at about 8 months after parturition. The timing of the increase in the concentrations of circulating progesterone and oestradiol provides evidence that the blastocyst reactivates and implants between 3.5 and 5 months of pregnancy in Australian sea lions, indicating an embryonic diapause of similar duration to that of other pinnipeds. This would suggest a prolonged postimplantation period of up to 14 months (to fit with the gestation period of 18 months reported for this species) the longest postimplantation period recorded for pregnancy in any pinniped.