Role of male-female interaction in regulating reproduction in sheep and goats.

The induction of synchronous ovulatory activity in anovulatory sheep and goats after the introduction of males, the 'male effect', has probably been used to advantage since these species were domesticated and the underlying physiological and behavioural mechanisms have been progressively elucidated over the past 50 years. Less well understood is the analogous effect of oestrous females on males. This review examines the nature and importance of these male-female interactions in sheep and goats, and describes the most important internal and external factors influencing the reproductive outcomes of such interactions. It is proposed that the male and female effects are both components of a self-reinforcing cycle of stimulation that, under ideal conditions, culminates in the synchronous very rapid onset (within days) of fertile reproductive activity. However, precisely because of the speed of this response, it is suggested that mechanisms have evolved to limit its efficacy, and thus prevent conception at inappropriate times. The complexity of these factors and the interactions between them are highlighted, and a broad conceptual framework for understanding them is proposed based upon an appreciation of variation in both the responsiveness of the target animal and the quality of the signal from the signalling animal.

Effect of season on LH secretion in ovariectomized Australian cashmere does.

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.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of nutrition on seasonal patterns of LH, FSH and testosterone concentration, testicular mass, sebaceous gland volume and odour in Australian Cashmere goats.

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 degrees S, 153 degrees 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.

The "female effect" in Australian cashmere goats: effect of season and quality of diet on the LH and testosterone response of bucks to oestrous does.

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 degrees S 153 degrees 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.

Testicular and epididymal sperm content in grazing Cashmere bucks: seasonal variation and prediction from measurements in vivo.

Each month, for 15 months, the testes and epididymides were recovered from five Australian cashmere bucks selected at random from a group of mature bucks (initial n = 116) at pasture (location 29 degrees S, 153 degrees E). The extent of seasonal change in testicular and epididymal sperm reserves was determined and indirect methods for predicting these reserves were developed. Paired testicular weight exhibited clear seasonal variation from 137 g in August to 269 g in February. The total elongated spermatid content of the testes, determined by homogenization, showed a very similar seasonal pattern, ranging from 13.8 x 10(9) in September to 36.2 x 10(9) in March. Seasonal changes of similar timing were observed for paired epididymal weight and sperm content. Although changes in total testicular spermatid content were largely the result of change in testicular weight (R2 = 0.72, P < 0.001), the elongated spermatid content of testicular parenchyma (mean, 127 x 10(6) g-1) exhibited significant seasonal variation with elevated values between February and June, suggestive of an increase in the efficiency of spermatogenesis. Daily sperm production, calculated by means of a spermatogenic time divisor for sheep, ranged from 2.76 x 10(9) in September to 7.23 x 10(9) in February. Scrotal circumference, scrotal volume and testicular length x diameter2 were identified as accurate predictors of testicular weight (R2 > or = 0.87) and sperm content (R2 > or = 0.70). The results demonstrate that: (a) cashmere bucks exhibit considerable seasonal variation in spermatogenesis associated primarily with changes in testicular mass but also with changes in the efficiency of spermatogenesis; and (b) indirect measures of testicular size are good predictors of testicular elongated sperm content. When the correct spermatogenic time divisor for goats is determined, such indirect measures may be used to predict daily sperm production.

Effect of immunization against melatonin on seasonal fleece growth in feral goats.

Four vaccination protocols were utilized to investigate the effects of immunoneutralizing circulating melatonin on the annual cashmere growth cycle and cashmere production in Australian feral goats. A fluctuating anti-melatonin antibody response, achieved by repeated booster vaccinations, resulted in an acceleration of the growth cycle in goats which exhibited a significant immune response, compared to sham-immunized controls. Responding goats showed two cycles of cashmere length growth in the first 16 months and increased annual cashmere production in the first year. However, in the second year, these effects were no longer apparent, suggesting either some form of desensitization to melatonin, or a diminished response due to declining antibody titre. The effects of immunization were observed in both sexes; the effect on cashmere length was greater in wethers than in does. Cashmere fibre growth in response to a continuously declining plane of specific antibody showed increased cycle frequency, albeit with a decreased amplitude; guard hair growth cycles were affected to a much lesser extent. Small transient peaks of specific immunity at the summer or winter solstice were without significant effect on cashmere growth. Immunization to provoke a persistent anti-melatonin antibody response at the winter solstice resulted in significantly increased greasy fleece weight, % cashmere yield, and mass of cashmere produced, but no change in fibre diameter in both sexes. Thus the timing of cashmere growth cycles in goats may be, at least transiently, altered by appropriately timed immunization against melatonin. The mechanism of pineal-mediated regulation of cashmere growth cycles may involve (i) entrainment of an endogenous rhythm by melatonin, or (ii) seasonal alteration of cashmere follicle sensitivity to the effect of melatonin.

Ovulatory activity in native Thai goats.

Ovarian activity was observed in native Thai goats run either alone, continuously with males, or intermittently with males at 56-day intervals between June 1985 and July 1986. Overall, the incidence of ovulation was highest in October and December (78.8%) and lowest in June (54.3%), with some does ovulating at every observation. The presence of males, either continually or intermittently, significantly increased the proportion of does ovulating throughout the year. The ovulation rate varied throughout the year, with the highest rate occurring in October 1985 (1.9) and the lowest rate in May and July 1986 (1.3). The implications of the study are discussed.

Pregnancy diagnosis in Thai native goats.

Pregnancy status was determined in two groups of native Thai goats, mated in either October (n = 116) or March (n = 37), by assay of the progesterone level in four plasma samples taken at 7 day intervals after the completion of mating. The progesterone level (P) in each sample was determined using facilities in a local hospital, and a commercial assay kit with human serum-based standards was used. The distribution of log(10) P yielded a discriminatory value of 2 ng/ml; any value below this level was assumed to indicate a follicular phase. Pregnancy diagnoses based on this criterion were 96.2% accurate. Diagnoses based on returns to service were not accurate, as 36.5% of pregnant does were recorded as returning. Real-time ultrasonic imaging of the March mated group was 100% accurate for pregnancies, but detection of twins was poor. The progesterone technique described here is useful in field studies where mating dates are not known, and where there is no access to an animal assay laboratory.

The influence of season of lambing and lactation on reproductive activity and plasma LH concentrations in Merino ewes.

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.

Studies of pituitary function in lactating ewes.

The release of LH from the pituitary of lactating ewes was studied. In Exp. 1, ewes were injected with 50 microng 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 the ovulations were recorded. The number of ewes in which an LH release was detected, and the amount released, declined between Day 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 microng 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.

Wastage of ova in young Merino ewes.

Eight sub-flocks each of 48 to 51 Merino ewes were mated for 18 days with 1 ram to each subflock. Four of the sub-flocks were of non-parous 1.5-year-old ewes and the other 4 were of parous 2.5-year-old ewes. Fertilisation rates for the subflocks of 1.5-year-old ewes varied from 83 to 94%, and the sub-flocks of 2.5-year-old ewes ranged from 81 to 94%. By day 29 post coitum 42% and 56% of 1.5-year-old ewes in sub-flocks 1 and 2 respectively were no longer pregnant. Embryonic mortality was low in other sub-flocks of 1.5- and 2.5-year-old ewes. Virtually all embryonic death occurred after day 12 post coitum. The sporadic occurrence of high ova wastage in maiden 1.5-year-old ewes in this experiment and in others is discussed in relation to the short duration of oestrus in young ewes and the great variation in service activity of rams.