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The effects of nutrition on the hypothalamo–pituitary–gonadal axis were studied in three groups of six mature Merino rams that were fed for 56 days with a ration that maintained their initial live mass (intermediate diet: 675 g chaff plus 175 g lupins), the same ration with a lupin supplement (high diet: 675 g chaff plus 825 g lupins), or about half of the intermediate ration (low diet: 475 g chaff plus 125 g lupins). Lupin seed provides a highly (95%) digestible source of energy and protein. Plasma concentrations of LH, FSH, testosterone and inhibin were measured in blood samples collected over 24 h on the day before dietary treatments began (day −1), then on days 0, 1, 5, 14, 28 and 56. Compared with the intermediate diet, the high diet significantly increased live mass within 14 days and testicular size within 28 days, and these differences increased steadily throughout the experiment. Plasma FSH concentrations and LH pulse frequency increased within 5 days, but these effects were maintained for only 14 days. Decreasing the nutritional status reduced live mass and testicular size within 7 days, led to a low LH pulse frequency that persisted throughout the experiment, but did not affect FSH concentrations. Significantly less testosterone was secreted over 24 h in the low dietary group than in the intermediate or high group until day 28. The high group tended to secrete more than the intermediate group, but only at the beginning of the experiment when LH pulse frequencies differed between these groups. The testosterone response to each endogenous LH pulse, or following an injection of ovine LH i.v. (200 ng kg⁻¹ live mass), was not related to testicular size or dietary treatment at any stage of the experiment. Similarly, plasma inhibin concentrations were not related to change of diet, despite large differences in testicular size. We concluded that the effects of nutritional status on testicular size in mature rams are at least partly mediated through changes in gonadotrophin secretion. Both increases and decreases in food supply affected LH pulse frequency, suggesting the involvement of hypothalamic mechanisms. However, the lack of an effect of a decrease in nutritional status on the secretion of FSH and inhibin and the inconsistent long-term relationship between LH pulse frequency and testicular size suggest that the effects of diet on testicular growth also involve mechanisms that are independent of changes in gonadotrophin secretion.

The fertility and viability of spermatozoa stored by male and female Gould's wattled bats, Chalinolobus gouldii, was investigated in a captive colony of ten bats (three males and seven females). Bats were housed in outdoor flight cages. Plasma progesterone concentrations, measured using double antibody radioimmunoassay, isolation experiments plus sperm motility and sperm membrane stability tests were used to evaluate the viability and fertility of stored spermatozoa. Mean plasma progesterone concentrations were lowest during midwinter (< 0.5 ng ml⁻¹) with a 20-fold increase recorded in late winter to early spring. During pregnancy, plasma progesterone concentrations increased to about 13 ng ml⁻¹ and returned to basal values soon after parturition. The results of the plasma progesterone assays and the isolation experiments indicate that female C. gouldii can store fertile spermatozoa for at least 33 days. The investigation of spermatozoa stored by male C. gouldii revealed that 6–7 months after peak spermatogenesis about 60% of the stored spermatozoa were motile and more than 60% had stable membranes, indicating that the spermatozoa stored by males were viable and likely to be fertile. The results of this study clearly indicate that both male and female C. gouldii are capable of storing fertile spermatozoa for prolonged periods.

The effects of nutrition on the testis were investigated in groups of five mature Merino rams that were fed either a sub-maintenance (low) diet or a supra-maintenance (high) diet for 69 days. Testosterone, oestradiol and inhibin were measured in blood plasma sampled simultaneously from jugular and testicular veins after an i.v. injection of 200 ng ovine LH kg⁻¹. Plasma concentrations of testosterone, inhibin and oestradiol were higher in testicular than in jugular vein plasma for both diets (P < 0.01). After the LH injection, jugular plasma testosterone increased more rapidly (P < 0.01) in rams fed the high diet than in rams fed the low diet. This was not seen in the testicular vein. Oestradiol concentrations were higher in rams on the high diet than in those on the low diet, in both the testicular (P < 0.0001) and the jugular vein (P < 0.02). Diet did not affect inhibin concentrations. Testes were surgically removed and processed for light microscopy. Testicular mass and seminiferous tubule length and diameter were higher with the high diet than the low diet (P < 0.01). The number of Sertoli cell nuclei per testis was also affected (high diet: 120 ±6×10⁸; low diet: 77 ± 7 × 10⁸; P < 0.001), whereas the proportion of testis occupied by Sertoli cell nuclei was not affected. The number of Leydig cells per testis was not affected by diet, but Leydig cells occupied a greater volume of testis in rams on the high diet than in those on the low diet (P < 0.001). The effects of nutrition on Leydig and Sertoli cells are consistent with changes in the endocrine and exocrine functions of the testis. The finding that Sertoli cell population was altered in adult rams may be explained by the GnRH-independent effects of nutrition.

The effects of dietary zinc deficiency on testicular development in young Merino rams (initial live mass, 22 kg) were tested. Four groups of five rams were fed ad libitum with diets containing 4, 10, 17 or 27 μg Zn g⁻¹. To control the effects of loss of appetite caused by zinc deficiency, a fifth group (pair-fed control) was fed the diet containing 27 μg Zn g⁻¹, but the amount of feed offered was restricted to that eaten voluntarily by the zinc deficient (4 μg Zn g⁻¹) rams they were paired with. After 96 days on the diets, epididymal and testicular masses did not differ significantly between the animals fed 10, 17 or 27 μg Zn g⁻¹ ad libitum, but were significantly lower in pair-fed controls, and lowest in the zinc-deficient animals. Testicular responsiveness to LH, as measured by testosterone production, increased substantially in most rams as the experiment progressed, the only exception being the zinc-deficient group, in which the response to LH was lower than in any of the other groups. Testicular concentrations of zinc and testosterone were lower in the zinc-deficient animals than in all the other groups. Plasma inhibin concentrations fell as the experiment progressed in rams fed 17 and 27 μg Zn g⁻¹ ad libitum, but not in the other groups. The pair-fed control rams had smaller seminiferous tubules and less lumen development than did the controls fed ad libitum (27 μg Zn g⁻¹). which were similar to the animals fed 10 or 17 μg Zn g⁻¹. In zinc-deficient rams, the tubule development was further retarded and the interstitial regions were more extensive than in the other groups. We conclude that the overall effect of zinc deficiency on testicular development is due to a combination of a non-specific effect (low gonadotrophin concentrations caused by the low feed intake) and a specific effect due to the lack of zinc. The zinc-specific effect is localized within the testis where it reduces the development of the capacity to produce testosterone, leading to low intratesticular concentrations of testosterone, a critical factor for the growth, development and function of the seminiferous tubules.

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.

We have developed an experimental model in which groups of ewes are simultaneously experiencing the first ovarian follicular wave of their oestrous cycle. We used this ‘first-wave model’ in a 2×2 factorial experiment (ten ewes per group) to study the effect of body condition (BC) and a short-term supplement on follicular dynamics and ovulation rate. The ‘first-wave’ was established by giving ewes three injections of prostaglandin (PG), 7 days apart. The 6-day supplement (lupin grain) began 2 days after the second PG injection and continued until the third. Follicles were studied by ultrasound, and blood was sampled to measure glucose and hormones. The supplement increased (P<0.01) the concentrations of glucose, insulin and leptin, decreased FSH concentrations (P<0.01) and tended to increase oestradiol concentrations (P=0.06). The supplement tended to increase the number of 3 mm follicles (P=0.06). Compared with low-BC ewes, high-BC ewes had more follicular waves (P<0.05), higher concentrations of insulin, leptin and IGF1 (P<0.05) and tended to have higher FSH concentrations (P=0.09). Leptin and insulin concentrations remained high until the end of supplementation in high-BC ewes, whereas they decreased after the third day of supplementation in low-BC ewes. In conclusion, high concentrations of metabolic hormones in fat ewes are associated with the development of more follicular waves. When a supplement is superimposed on this situation, changes in glucose and metabolic hormones allow more follicles to be selected to ovulate.