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P. Chemineau

Summary. The characteristics of the oestrous and ovarian cycles of local goats were studied over 2 years, on 96 females in March, 60 in July and 100 in November. After 3 weeks of separation between sexes, the females with inactive ovaries were identified and harnessed males were introduced. Detection of oestrus was undertaken daily and the date and rate of ovulation were checked at laparoscopies.

The proportion of females with non-cyclic ovaries before the mating period varied according to the season and whether the females were nulliparous or suckling. Among the females with inactive ovaries before the mating period, 97% ovulated 2·8 days after the introduction of males; 68% of these initial ovulations were accompanied by oestrus and 76% resulted in short luteal phases (5·3 days) followed by a second ovulation accompanied by oestrus 89% of the time. The proportions of initial ovulations with oestrus and of initial ovulations followed by a short luteal phase were in linear relationship with the proportion of females with non-cyclic ovaries before the mating period. For the females with cyclic ovaries before the mating period, the distribution of first oestrus during the 8 days after the introduction of males was significantly different from the expected uniform distribution. A possible luteolytic action of teasing was suspected. The fertility of females in all groups was high (> 79%). Litter size was not different for non-cyclic and for cyclic females.

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S. Le Corre and P. Chemineau

The role of dopaminergic and serotonergic systems on LH secretion was investigated in Ile-de-France ewes under different artificial inhibitory photoperiodic regimens. All animals were ovariectomized at the end of the breeding season, chronically treated with an oestradiol implant, and subjected to various changes in daylength for 9 months to inhibit or stimulate their LH secretion. Plasma LH concentration was assessed by taking blood samples twice a week throughout the experiment. The effects of acute intravenous injections of the dopaminergic2 receptor antagonist pimozide (0.08 mg kg−1) and the 5-hydroxytryptamine2 (5HT2) receptor antagonist cyproheptadine (3 mg kg−1) on LH pulsatility were assessed during challenges in four different situations: (1) long days (LD); (2) before short-day response (SD); (3) during refractoriness to short days (RSD); and (4) during inhibition by long days (ILD). LH in blood samples collected twice a week remained low during long days (0.59 ± 0.03; mean ± sem), increased 45 ± 1.5 days after the onset of short days and decreased 132 ± 4.9 days later when ewes became refractory to short days, whereas ewes subjected to long days after 91 short days stopped their neuroendocrine activity 19 days earlier (113 ± 4.7) (P < 0.01). In comparison with the pre-injection period, pimozide significantly increased the mean number of pulses in SD and RSD ewes, but not in LD and ILD ewes: SD: 0 versus 0.45 pulses in 4 h (P < 0.02); RSD: 0 versus 0.9 (P = 0.05). Cyproheptadine significantly increased the mean number of pulses in SD and RSD ewes: SD: 0 versus 1 (P < 0.008); RSD: 0 versus 1.5 (P = 0.03). An effect of cyproheptadine was shown in LD ewes (0 versus 0.5 (P < 0.03)), but it was less marked than in the same ewes under short-day photoperiod (SD ewes; P < 0.05). In ILD ewes, a small increase was observed (0 versus 0.33 (P = 0.05)) but it was less than in RSD ewes (P < 0.03). These results support the hypothesis of an inhibitory role of dopaminergic and serotonergic systems on LH pulsatile release and suggest that refractoriness to short days is due to activation of these two systems.

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J. A Delgadillo and P. Chemineau

Summary. This study was performed to determine whether rapid alternation between long and short days abolished seasonal variations in the activity of the hypothalamo-pituitary-testis axis observed normally in Alpine and Saanen male goats during the year. Three groups of 6 males were used: group 1 remained in open sheds under the natural annual change in daylength from 16 h of light (long day) to 8 h of light (short day). Group 2 was exposed to 1 month of long days alternated with 1 month of short days; and group 3 to 2 months of long days alternated with 2 months of short days. In group 1, blood samples were taken in December, February and June; in groups 2 and 3, samples were obtained once during short and long days for the melatonin assay. For luteinizing hormone and testosterone determinations monthly samples from group 1 were obtained from September to August while, in groups 2 and 3, blood samples were taken on 4 occasions during long and short days. Weekly blood samples were taken from all groups during the whole of the experiment to measure prolactin and testosterone concentrations.

Melatonin profiles indicated that secretion by the pineal gland of male goats from the treated groups adapted to rapid changes in daylength: duration of nocturnal secretion was close to that of the dark period. Treated goats were also able to transduce this signal adequately and always responded to long days by increasing their prolactin concentration (mean ± s.e.m.; group 2: 62·4 ± 6·8 ng/ml; group 3: 102·3 ± 15·7 ng/ml) and to short days with a decrease in prolactin concentrations (35·0 ± 3·6 and 46·1 ± 9·5 ng/ml, respectively). In the treated groups, luteinizing hormone pulse frequency varied with day length. In group 2, it was higher in long days (1·1 ± 0·3 pulses in 8 hours) than in short days (0·7 ± 0·3) while, in group 3, this frequency was higher in short days (1·9 ± 0·3) than in long days (0·5 ± 0·2). Testosterone secretion also varied with daylength; in group 2, the testosterone concentrations were maximum during long days (5·8 ± 1·4 ng/ml) while in group 3 the maximum testosterone concentrations occurred during short days (6·4 ± 1·2 ng/ml).

These results lead to the conclusion that rapid alternation oflong and short days either attenuated (group 3) or prevented (group 2) seasonal changes in the activity of the hypothalamo-pituitary axis. The maintenance of high testicular weight and high sexual activity was due to periods of gonadotrophin stimulation of the testis alternating rapidly with periods of quiescence.

Keywords: seasonality; luteinizing hormone; testosterone; photoperiod; goat

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A. J. Sempéré, R. Mauget and P. Chemineau

Summary. Concentrations of progesterone and luteinizing hormone in plasma were analysed for two consecutive years in samples from nonpregnant female roe deer. Three animals were treated with monthly prostaglandin injections (325 μg cloprostenol) from October 1989 to April 1990 and from October 1990 to March 1991, and three were kept as controls. In control animals, a small increase in progesterone concentrations in July 1990 occurred at the same time as the commencement of the rut in other husbanded roe deer. In prostaglandin-treated animals, progesterone concentration was high at the time of the rut and remained so until late February 1990. After the next rut (August 1990), progesterone concentration remained high until March 1991. Between October and February–March, injections of prostaglandins induced dramatic, but temporary (lasting 72 h), decreases in plasma progesterone concentrations, indicating luteal regression and subsequent ovulation. We infer that roe deer can ovulate repeatedly and should therefore not be regarded as an obligate monoestrous species.

Keywords: corpus luteum; luteinizing hormone; progesterone, prostaglandin, roe deer

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P. Chemineau, E. Normant, J. P. Ravault and J. Thimonier

Summary. Thirty-two out-of-season Saanen dairy goats were involved in a 2 × 2 factorial experiment using (1) extra-light treatment (equivalent to long days) from 18 January to 19 March, at the end of gestation and the onset of lactation and (2) daily melatonin injections (equivalent to short days) from 20 March to 30 June. Hence, there were 4 groups of 8 goats each: CC (control–control), EC (extra-light–control), CM (control–melatonin) and EM (extra-light–melatonin). In each group teasers (males and androgenized females) were introduced on 30 May. Serial blood samples were taken for measurement of LH pulsatility on 30 April and 30 May. Ovarian activity was followed by plasma progesterone assay and laparoscopy. Oestrous behaviour was checked daily from 30 May to 15 July.

The number of LH pulses was not modified by the treatments (extra light or melatonin). Melatonin treatment increased the basal concentration of LH (Groups CC + EC = 0·30 ng/ml; Groups CM + EM = 0·38 ng/ml; P < 0·02) and the amplitude of pulses (Groups CC + EC = 1·24; Groups CM + EM = 2·44 ng/ml; P < 0·02); the highest amplitude was observed for females in Group EM. Melatonin-treated females ovulated earlier after introduction of teasers than did untreated goats (Groups CM + EM = 2·3 days; Groups CC + EC = 6·1 days; P < 0·001), but treatments did not modify ovulation rate (mean 2·1) or percentage of goats experiencing a short luteal phase. Plasma progesterone concentration during this short luteal phase was higher in melatonin-treated goats (Groups CM + EM = 1·61 ng/ml; Groups CC + EC = 1·05 ng/ml; P < 0·05). Ovarian cyclicity persisted longer in Group EM goats than in the other groups: at 2·5 months after introduction of teasers 75% of the females were still ovulating compared to 12% in Group CM and none in Groups CC or EC (P = 0·003). The number of goats which exhibited oestrus on two or more occasions was higher after melatonin-treatment than in controls (P = 0·013).

We conclude that exposure to long days is essential before melatonin treatment to obtain and maintain maximum sexual activity in the out-of-season dairy goat.

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P. Chemineau, G. B. Martin, J. Saumande and Elisabeth Normant

Summary. In Exp. 1, the changes in pulsatile LH secretion at the onset of the breeding season were observed in 20 intact, mature Saanen does. Blood was sampled every 20 min for 6 h each week from the beginning of August until the onset of ovulatory activity, as evidenced by cycles in plasma progesterone. The first doe ovulated at the end of August and all were cycling by the end of September. As the first ovulation approached, LH pulse frequency increased by 67% and mean levels of LH increased by 47%. These changes were progressive rather than abrupt. In Exp. 2, seasonal changes in the inhibition of pulsatile LH secretion by ovarian steroids were studied in ovariectomized Saanen does. The animals were untreated (N = 4) or given subcutaneous oestradiol implants (N = 4) and blood was sampled every 10 min for 6 h, twice during the breeding season and twice during the anoestrous season. In each season, the second series of samples was taken after the animals had been treated with progesterone, administered by intravaginal implants. Season did not significantly affect LH secretion in goats not treated with oestradiol, but LH pulse frequency was 54% lower during the anoestrous season than during the breeding season in oestradiol-treated goats. Mean LH concentrations were affected in the same manner as pulse frequency, but pulse amplitude was increased by oestradiol treatment in both seasons. Progesterone had no detectable effect on LH secretion in either season. In Exp. 3, the response to repeated melatonin injections at a set time after dawn was investigated in 11 oestradiol-treated, ovariectomized goats. They were placed under a regimen of long days (16 h light:8 h dark) and 1 month later 6 of them were injected daily (10 h after 'dawn') with 2 mg melatonin. The other 5 animals served as controls. Blood samples (every 10 min for 6 h) were taken just before and 38 and 72 days after the start of melatonin treatment. As the experiment progressed, LH pulse frequency increased by 20% in melatonin-treated goats but decreased by 43% in controls. Mean LH values were maintained in melatonin-treated females but decreased in the control group. Melatonin did not affect pulse amplitude.

The results of the experiments with ovariectomized does suggest that seasonal reproductive cycles in the goat are caused by changes in the duration of melatonin secretion at night, which induce alterations in the intensity with which oestradiol inhibits LH secretion. In turn, this may be responsibile for the gradual changes in the frequency of LH pulses observed in entire does. The frequency of LH pulses is one of the most important endocrine signals controlling ovarian activity so would form the final link in the chain connecting environmental and reproductive cycles.

Keywords: LH; goat; melatonin; steroids; season

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A. Daveau, B. Malpaux, Y. Tillet, G. Roblot, R. Wylde and P. Chemineau

An experiment was conducted to determine whether active immunization against melatonin could modify the perception of abrupt photoperiodic changes in ewes. Two groups each containing six intact Ile-de-France ewes were submitted to alternate periods of short days for 2.5 months and long days for 2.5 days for about 70 weeks. Three series of active immunizations against a melatonin conjugate were carried out during the first of the three long-day periods. Control ewes were actively immunized at the same time against human serum albumin. Blood samples were taken once a week throughout the experiment to measure antibody titre and affinity, and prolactin and progesterone concentrations. Sera of all treated ewes demonstrated higher antibody titres than those of control ewes. Antisera were highly specific, as evidenced by the absence of displacement of iodinated melatonin in the presence of ten melatonin metabolites. Significant effects of photoperiod and of the interaction between treatment and photoperiod on prolactin concentration were detected. Prolactin concentrations in plasma of the control ewes were high during long days and low during short days. However, in the treated ewes, with the exception of the first period of long days, prolactin concentrations were not influenced by photoperiodic changes. Ovulatory activity of control ewes, as demonstrated by progesterone measurements, was stimulated by short days and inhibited by long days. In contrast, ovulatory activity of treated ewes, after a response identical to that of control ewes after the first photoperiodic shift from long to short days, showed a complete desynchronization of ovulatory activity relative to photoperiodic changes. Immunization against melatonin can therefore modify the influence of artificial photoperiodic changes on prolactin secretion and ovulatory activity in ewes.

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B. W. Brown, Y. Cognie, P. Chemineau, N. Poulin and O. A. Salama

Summary. The microsphere technique was used to obtain estimates of ovarian capillary blood flow near ovulation, in 8 seasonally anoestrous ewes, which were induced to ovulate by GnRH therapy. Plasma progesterone concentrations were monitored in jugular blood sampled between Days 4 and 7 after the onset of the preovulatory LH surge. The ewes were then slaughtered. Three of the ewes were treated with a single injection of 20 mg progesterone before GnRH therapy. In these ewes and 1 other, plasma progesterone values increased after ovulation and reached 1·0 ng/ml on Day 7 following the preovulatory LH surge (normal, functional CL), whilst in the other 4 ewes progesterone concentrations increased initially then declined to 0·5 ng/ml by Day 7 (abnormal CL).

In the ewes exhibiting normal luteal function, the mean ovarian capillary blood flow was significantly greater (P < 0·01) than that for ewes having abnormal luteal function. Irrespective of the type of CL produced, capillary blood flow was significantly greater (P < 0·05) in ovulatory ovaries than in non-ovulatory ovaries.

These findings indicate that the rate of capillary blood flow in ovaries near ovulation may be a critical factor in normal development and maturation of preovulatory follicles and function of subsequently formed CL.

Keywords: blood flow; anoestrus; sheep; gonadotrophins; ovary