Summary. Groups of Merino ewes which were lactating for 40 days (Group I) or had had their lambs removed at birth (Group II) after lambing in the winter (June) or spring (November) were fed on a high plane of nutrition. Ovarian inspections were carried out at 15 and 30 days after lambing and plasma LH levels were measured at 6-h intervals for 20–30 days.

First ovulation was earlier in ewes lambing in the winter (16·6 days, range 11–26) than in the spring (24·7 days, range 15–30) but there was no difference in the number of ewes ovulating. LH levels were higher in winter-lambing ewes (2·79 ± 3·4 ng/ml) than in those lambing in the spring (1·78 + 0·23 ng/ml). LH peaks were usually associated with an ovulation in spring lambing ewes but were not consistently so in the others.

More ewes ovulated in Group II (72%) than in Group I (40%) but the mean time of first ovulation was similar. In the winter-lambing ewes the mean daily LH concentration was 2·40±0·32 ng/ml in Group I and 3·18±0·31 ng/ml in Group II but there were no differences between the spring-lambing ewes (I, 1·75±0·20 ng/ml; II, 1·80±0·26 ng/ml). There were more elevations in LH levels in Group II ewes (64%) than in Group I ewes (43·8%).

After lambing the LH levels increased slowly, indicating a gradual recovery of pituitary function.

Summary.

Spacing of zygotes, loss of the zona pellucida, and appearance of localized areas of increased vascular permeability at the implantation sites in the uterus were observed in groups of mice examined at 2-hr intervals from 10.00 hours to midnight on Day 4 of pregnancy, and at 02.00, 08.30 and 15.00 hours on Day 5. All the events examined had a 6- to 8-hr variation in their time of occurrence.

Studies of interrelationships between the zygote and the uterus require a precise knowledge of the timing, variation and sequence of the events leading up to implantation in any one species. Previous studies of preimplantation phenomena in the rodent have been based on relatively small numbers of animals examined at irregular intervals during the periods of interest.

Summary.

Three experiments were conducted to examine the effects of site of insemination, sperm motility and contractions of the genital tract on the transport of spermatozoa in the ewe.

In the first experiment, the proportion of ewes from which spermatozoa were recovered from the Fallopian tubes was reduced, both in ewes receiving oxytocin (1 ·0 or 10·0 i.u., intramuscularly) and in those in which only shallow insemination could be achieved.

The second experiment examined the effects of sperm motility (live versus dead spermatozoa), inhibition of genital tract contractions (halothane anaesthesia : −, + ) and stimulation of genital tract contractions (oxytocin injections: −, +). Sperm motility was found to be the most important factor affecting transport through the cervix. Oxytocin had little effect, but following insemination with immotile spermatozoa, inhibition of genital tract contractions reduced the number of spermatozoa recovered from both the cranial cervix and Fallopian tubes.

The effects of site of insemination (external versus internal cervical os) and sperm motility (live versus dead spermatozoa) were examined in the third experiment. Few spermatozoa were found between the mucosal folds of the cervix when immotile spermatozoa were used. Large numbers of spermatozoa were recovered from both the cervix and Fallopian tubes after insemination at the level of the internal cervical os, particularly following the use of motile spermatozoa.

The results demonstrate the importance of sperm motility, particularly in relation to the establishment of the cervical population of spermatozoa.

An experiment was conducted to define the seasonal changes in LH secretion in ovariectomized does with oestrogen implants and the effect of immunization against melatonin. Fifteen mature Australian cashmere goats were ovariectomized and given either no further treatment or one or two implants containing oestradiol; another similar group of 15 does were immunized against melatonin before ovariectomy and oestrogen treatment. LH concentrations and livemasses were recorded every week for 2 years. Livemasses of both groups showed a distinct seasonal pattern with a summer maximum and a winter minimum irrespective of treatment. LH concentrations also showed distinct seasonal patterns with a significant interaction between the number of implants and the time of the year. In the nonimmunized does, the presence of a constant low dose of oestrogen (one implant) resulted in low concentrations of LH except from May to August, the normal period of spontaneous ovulatory activity in intact does. In contrast, nonimmunized does receiving a high dose of oestrogen (two implants) showed a rise in LH concentrations in February, and concentrations remained high until August. Immunization against melatonin abolished this differential LH secretory pattern, and both doses of oestrogen were associated with a short period of high LH concentration between May and September. These results indicate that a negative feedback effect of oestrogen results in low LH secretion for most of the year and that hypothalamic sensitivity to LH decreases for only a short period between May and August. It is suggested that the early increase in LH secretion in does with two oestrogen implants is due to a positive oestrogen feedback mechanism that may depend on a photoperiodic signal for activation.

Summary. The release of LH from the pituitary of lactating ewes was studied. In Exp. 1, ewes were injected with 50 μg oestradiol benzoate (OB), 2·0 mg testosterone propionate (TP) or oil only (control) on Days 5,10 or 20 after lambing. LH was measured in peripheral plasma samples obtained 20–38 h after treatment, and ovulations were recorded. The number of ewes in which an LH release was detected, and the amount released, declined between Days 5 and 20 after OB treatment but increased after TP treatment. The releases of LH were not always accompanied by ovulation and the incidence of ovulation was higher in ewes treated with TP. In Exp. 2, lactating ewes were injected with 1 or 5 (at 2-h intervals) doses of 50 μg Gn-RH, on Days 12 or 25 after lambing. LH was measured in peripheral plasma samples collected every 2 h for 10 h and every 3 h for a further 70 h. Release of LH occurred in all ewes, the amount being greater in ewes receiving multiple injections and in ewes treated on Day 25. The incidence of ovulation was higher after treatment on Day 25. Multiple injections of Gn-RH appeared to reduce the incidence of abnormal corpora lutea.

The effects of season, diet and exposure to oestrous females on LH and testosterone secretion were examined in mature cashmere bucks to determine whether there is a seasonal cycle of LH and testosterone secretion, and whether this can be modulated by long-term differential nutrition and exposure to oestrous females. Three-year-old bucks were individually housed under natural photoperiod at 29°S 153°E and fed diets of high (crude protein 17.6%, metabolizable energy 8.3 MJ kg⁻¹) or low (crude protein 6.9%, metabolizable energy 6.6 MJ kg⁻¹) quality for 16 months ad libitum (n = 6 per treatment). Blood samples were collected to determine pulsatile LH and testosterone secretion immediately before experimental feeding, one month later, and every second month thereafter. Samples were collected for an 8 h period on successive days with the bucks isolated on the first day and each exposed to a single oestrous doe for the duration of the second day. In the absence of oestrous females, bucks exhibited a circannual pattern of secretion for both hormones with pulse frequency and mean concentrations highest in late summer and autumn and lowest in late winter and spring. Testosterone pulse amplitude followed a similar pattern, but LH pulse amplitude was highest in spring and lowest in autumn, indicating a seasonal shift in the relationship between the two hormones. Exposure to oestrous does increased LH and testosterone secretion depending on both season and diet. Responses were evident during summer, autumn and early winter, with bucks on a high quality diet exhibiting an earlier and more prolonged period of responsiveness than did bucks on a low quality diet, peaking in February compared with June. The magnitude of the LH and testosterone response was also significantly greater in bucks on a high quality diet. Weight loss during autumn appeared to reduce responsiveness in both treatments. These results demonstrate that there is a seasonal cycle in LH and testosterone secretion in mature cashmere bucks, and that nutrition and oestrous females are powerful modulators of the secretion of these hormones in a seasonally dependent way.

The effects of season and diet on LH, FSH and testosterone concentrations, testicular mass, sebaceous gland volume and male odour were examined in mature Australian cashmere goat bucks fed ad libitum with diets of low or high quality for 16 months under natural photoperiod at 29°S, 153°E (n = 6 per treatment). Each week plasma was sampled, the bucks were weighed, scored for male odour and assessed for testicular mass based on scrotal circumference. Each month a skin sample was taken from the occipital region for histological assessment of sebaceous gland volume. For each variable there was a clear circannual cycle that was significantly influenced by dietary treatment. In bucks fed the low-quality diet, the timing of seasonal changes in LH and testosterone concentration, sebaceous gland volume and odour score was similar, with a mid-autumn peak. In each case the high-quality diet advanced, extended the duration and increased the magnitude of the seasonal increase. FSH concentrations peaked in late spring (in bucks on the high-quality diet) or summer (in bucks on the low-quality diet), reaching a nadir in early winter. The high-quality diet significantly increased concentrations only in the last 2 months of the experiment (spring). There was no overall association between these variables and change in testicular mass; instead, it was strongly correlated with voluntary feed intake and change in body mass, themselves subject to seasonal variation with a winter or spring peak. The high-quality diet induced large increases in body mass and testicular mass during the first months of the experiment without influencing the seasonally low concentrations of FSH, LH and testosterone present at the time. These results demonstrate that the male, like the female, Australian cashmere goat, exhibits marked reproductive seasonality, and that nutrition is a powerful modulator of the seasonal cycle. They suggest that testosterone concentration, sebaceous gland volume and odour score are ultimately dependent upon LH secretion, which appears to be under strong seasonal (photoperiodic) control, with the effects of enhanced nutrition limited to periods when photoperiodic inhibition is waning. However, seasonal regulation of testicular mass, and therefore sperm production, appears to be primarily dependent on changes in voluntary feed intake and growth, with the seasonal cycle of testicular mass more a consequence of the seasonal appetite or growth cycle than of changing gonadotrophin concentrations.