Effect of melatonin implants on secretion of luteinizing hormone in intact and castrated rams

Rams were treated with melatonin implants in 2 experiments designed to examine the control of reproductive seasonality. In Exp. 1, rams (n = 12) were allocated to 3 treatment groups: 2 groups were treated with 2 melatonin implants per ram for 4 months from 11 November (N) and 9 December (D) and the remaining group was untreated (C). The seasonal increase in luteinizing hormone (LH) pulse frequency and testes size was advanced in Groups N and D. A second seasonal cycle in LH secretion and testes size occurred in Groups N and D after melatonin implants became exhausted. In Exp. 2, rams (n = 20) were allocated to 4 treatment groups: 10 rams were castrated on 6 October and 1 group of entire rams (EM) and one group of castrated rams (CM) were treated with 2 melatonin implants per ram each month from 3 November until 8 January. The other group of entire rams (EC) and castrated rams (CC) was untreated. An increase in LH pulse frequency occurred after castration. Melatonin treatment increased LH pulse frequency in entire rams and reduced LH pulse frequency in castrated rams. The results demonstrated that the advanced reproductive development as a result of treatment with melatonin implants was due to an effect of melatonin on the hypothalamic pulse generator to increase LH pulse frequency. The ability of melatonin to influence LH pulse frequency in entire and castrated rams indicated that an effect of melatonin on the hypothalamic pulse generator is independent of testicular steroids.     

Induction of early breeding in red deer (Cervus elaphus) by melatonin

Lactating (N = 12) and non-lactating (N = 6) red deer hinds and one stag at pasture were given concentrates (500 g/head) containing melatonin (5 mg/head) daily at 16:00 h from 18 June to 16 October. The stag shed the antler velvet and started rutting 5 weeks ahead of untreated stags, and hinds had their first oestrus and ovulation of the breeding season in mid-September, 5 weeks in advance of control lactating (N = 9) and non-lactating (N = 5) hinds. Treated hinds were allowed to mate with the treated stag and control hinds ran in an adjacent paddock with an untreated stag. All hinds became pregnant during the study with all but 2 melatonin-fed hinds (1 lactating, 1 non-lactating) and 1 control hind (lactating) conceiving at the first oestrus. Melatonin-treated hinds lost slightly more live weight than did controls from June to November, but their suckled calves grew throughout at a rate similar to those of control hinds.     

Induction of early rutting in male red deer (Cervus elaphus) by melatonin and its dependence on LHRH

Eight red deer stags, 2 control, 3 control-immunized (i.e. a low titre of LHRH antibodies after active immunization 2 years earlier) and 3 superior cervical ganglionectomized, were given a s.c. implant of melatonin in May at the nadir of the sexual cycle; 5 other stags remained untreated. All the melatonin-treated animals shed the velvet-like skin from the antlers in June or July at least 1 month before the untreated controls, and had an early increase in blood plasma testosterone concentrations. The treated stags were also precocious in the development of rutting behaviour, although this inductive effect was blocked dramatically in the control-immunized stags after a booster immunization against LHRH; these animals failed to show any further reproductive development and cast their antlers. It is concluded that continuous exposure to melatonin in early summer will induce premature seasonal testicular development, an effect dependent on the secretion of LHRH, and similar to that produced by exposure to short daylengths.     

Relationships between Behaviour and Antler Cycle Timing in Red Deer

The factors affecting the stag social hierarchy and antler cycle timing in a herd of red deer were analysed. The analysis was based on behaviour records of the herd between 1972 and 1983. The alpha stag was not usually the oldest stag present. Changes in rank were commoner in periods of hard antler than during velvet periods. The frequency of rank changes was correlated with the number of stags present but not with the number of hinds; it was also positively related to indicators of the level of aggression such as the incidence of antler breakage, the number of harem-holding stags per rut and the incidence of post-casting rank loss. The number of stags killed in fights was not correlated to any of the indicators of aggression except the number of harem-holders per rut. Rank loss after antler casting and the change of harem-holding stags during the rut were both relatively rare events indicating year-round, stable social relationships in the herd. The relationships between rank and casting date and between rank and cleaning date previously reported were related to the level of aggression among the deer. The higher the level of aggression, the closer the relationship between rank and the timing of the antler cycle. The small difference in the level of aggression between the periods of casting and cleaning is thought to be the result of the seasonally different social background. The number of hinds present did not appear to affect antler casting, antler cleaning or the general indicators of the level of aggression. It is concluded that the results support the previously advanced hypothesis that behaviour modulates antler cycle timing in Cervids.     

Effects of melatonin implants on plasma concentrations of testosterone, thyroxine and prolactin in the male silver fox (Vulpes vulpes)

Melatonin administration in the form of slow-release implants advanced breeding activity in silver fox males when treatment began in June. Plasma testosterone concentrations were significantly higher in treated animals than in controls from September to November, whereas in February and March they were significantly lower. Plasma prolactin concentrations were significantly reduced immediately following melatonin treatment in June but increased to greater levels than control values and 'peaked' after 7 months. This 'peak' was associated with a rapid decrease in testosterone secretion. The normal seasonal spring rise in prolactin secretion was prevented by melatonin administration. Thyroxine values decreased and were significantly lower after 2 months of melatonin treatment.     

Induction and persistence of pituitary and ovarian activity in the out-of-season lactating dairy goat after a treatment combining a skeleton photoperiod, melatonin and the male effect

Thirty-two out-of-season Saanen dairy goats were involved in a 2 X 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 less than 0.02) and the amplitude of pulses (Groups CC + EC = 1.24; Groups CM + EM = 2.44 ng/ml; P less than 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 less than 0.001), but treatments did not modify ovulation rate (mean 2.1) or percentage of goats experiencing a short luteal phase.(ABSTRACT TRUNCATED AT 250 WORDS)     

甲状腺功能对调节雄性马鹿体重和繁殖活动季节性变化的研究

本研究探讨了甲状腺功能对雄性马鹿体重和繁殖活动季节性变化的调节作用,试验１从１９８８年１月（夏季）开始到１９８９年６月（冬季）结束,对照组５头正常鹿体中,血浆Ｔ３水平具有明显的季节性变化（Ｐ＜０．０１）,在秋季和冬季较低,春季至秋季早期较高,而３头甲状腺摘除（ＴＨＸ）鹿血浆Ｔ３水平在１９８８年６月后（冬季）降低到不可测水平。在１９８８年９月以前,二组鹿的体重,睾丸直径和血浆睾酮水平的季节性变化趋势     

Effect of genotype at the MTNR1A locus and melatonin treatment on first conception in Sarda ewe lambs

A sample of 423 Sarda ewe lambs from three different farms was used to evaluate the effect of one or two melatonin implants on the time of first conception. On each farm, 141 animals were divided into three groups. On June 30 these animals received either no treatment (Group C), 18 mg melatonin (Group M1, one implant), or 18 + 18 mg melatonin (Group M2, two implants). Thirty-five days after treatment, rams were introduced in the ewe lambs flock and subsequently removed after 40 days. Lambing dates were recorded between 150 and 190 days from the first day of male introduction. Genotyping and sequencing of the MT1 exon 2 were carried out to analyze the structure and the possible influence of the MT1 receptor gene on reproductive response to melatonin treatment. Melatonin-treated animals had a higher rate of pregnancy (P < 0.05) and lambed earlier (P < 0.05) compared with untreated animals. Single nucleotide polymorphisms were found in exon II of MT1 gene at positions C606T and G612A leading to genotypes C/C, C/T or T/T and +/+, +/− and −/−, respectively. Melatonin-treated animals of +/+ genotype showed a higher number of pregnancies (P < 0.05) and lambed earlier (P < 0.05) compared to untreated animals of the same genotype. Melatonin treatment did not affect reproductive activity in any other genotype analyzed. No correlation between genotype and the time of first conception was found in untreated animals. Concluding data revealed the positive effect of melatonin treatment on the time of first conception in ewe lambs and highlighted that +/+ genotype is able to influence reproductive response to melatonin treatment.     

The effect of cyproterone acetate on the antler cycle in red deer (Cervus elaphus L.)

The aim of the study was to test the effect of antiandrogen, cyproterone acetate (CA) on the antler cycle in the red deer (Cervus elaphus). CA was administered to three adult red deer stags (Edward, Fuks and Gacek) in weekly intervals. Edward and Fuks were given 600 mg + 600 mg of CA, whereas Gacek was given 600 mg + 300 mg. CA was injected during the hard antler phase: in mid-October (Edward), at the end of November (Fuks) and at the end of January (Gacek). CA caused the antler casting 17 to 22 days after the first injection. In all stags, the casting of antlers was followed by a period of intensive growth of new antlers. Edward was given CA at the end of October. This treatment was responsible for occurrence of the two antler cycles in the year of the experiment. When CA was administered during the middle of the hard antler phase an additional short antler cycle occurs followed by new antler growth. CA treatment in the later part of hard antler phase may cause a prolonged antler cycle.     

Antler size and fluctuating asymmetry in red deer (Cervus elaphus) stags and probability of becoming a harem holder in rut

Red deer hinds play a significant role in selecting stags for mating. We tested the hypotheses that in red deer ( Cervus elaphus ) the probability of becoming a harem holder (and hence achieving reproductive success) occurs in stags bearing larger, branched antlers and showing low fluctuating asymmetry (FA). Eleven antler characteristics were measured; absolute and relative FA were calculated on 51 cast antler sets from 19 individually recognized stags. Probability of becoming a harem holder (PBHH) was originally analysed separately, i.e. for antler size and FA of each antler characteristic and calculated factors for both antler size and FA. If analysed separately, large antler size and low relative but high absolute FA increased PBHH. When we combined antler size and FA of antler characteristics in one model using antler size and FA factors, however, PBHH and achieving reproductive success were mainly dependent on increasing antler size and enhanced antler branching rather than on FA. We conclude that in contrast to antler size, FA is unlikely to play any significant role in sexual selection as an indicator of individual quality.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 59–68.     

Effect of melatonin implants on reproduction in the male silver fox (Vulpes vulpes)

In June 1987, when the testes were fully regressed, 5 males were given s.c. implants of 40 mg melatonin. The same treatment was repeated in August and October 1987. Five males served as controls. Plasma concentrations of melatonin increased significantly in treated males and were still elevated at the end of the study in April 1988. The changes in testicular volume and blood plasma concentrations of testosterone in response to GnRH indicated that melatonin administration promoted testicular development. However, testicular regression was observed earlier in treated than control animals, perhaps because of refractoriness to melatonin or to a down-regulation of melatonin receptors. Semen was collected and frozen in November 1987, 2 months ahead of the natural breeding season, from the melatonin-treated males, and 10 blue fox vixens were inseminated the following breeding season: 9 vixens conceived, and the average litter size was 7.6 +/- 0.5. The results demonstrate that melatonin treatment initiated during exposure to naturally long days (a) promotes testicular development in a way similar to an artificial short photoperiod and (b) may induce a refractory condition after an extended period of treatment.     

The induction of male sexual behavior in red deer (Cervus elaphus) by the administration of testosterone to hinds and estradiol-17β to stags

One-gram implants of testosterone were placed subcutaneously in two adult intact and one castrated red deer hinds, and 100-mg implants of estradiol-17β were given to three castrated and two intact red deer stags. Their sexual behavior was then observed in the wild and in captivity for up to 3 years. Testosterone initially produced prolonged and intense estrous behavior in the hinds; this gradually gave way to behavior normally shown only by rutting stags, such as flehmen, herding threats, and roaring. Testosterone-implanted hinds rose in the dominance hierarchy as measured by competition for food. Pregnancy, or the administration of progestagens, suppressed most of this testosterone-induced behavior. Testosterone also induced development of male secondary sexual characteristics such as formation of small antler pedicles (but not antlers), hypertrophy of the clitoris and neck musculature, and development of a neck mane and male rutting odor. Estradiol-17β mimicked the behavioral effects of testosterone when given to castrated stags, stimulating all components of rutting behavior. In intact stags, the only effects were to abolish antler casting and stimulate roaring; normal rutting behavior continued unchanged. In contrast to the effects of testosterone, estradiol-17β did not influence the social status of either intact or castrated stags. The distinctions between the behavioral effects of androgens and estrogens are ill defined and are determined more by the prior sexual differentiation of the brain and the duration of steroid treatment, than by the nature of the steroid.     

Effect of intravaginal implants of melatonin on the onset of ovarian activity in adult and prepubertal ewes

Melatonin was administered intravaginally in Silastic tubing to adult and prepubertal ewes. In Exp. 1, ewe lambs (born early March) were given intravaginal melatonin implants at a mean age (+/- s.e.m.) of 7.5 +/- 0.1 weeks (Group E, N = 10) or 19.4 +/- 0.2 weeks (Group L, N = 10). The third group (Group C, N = 10) received empty implants. In Exp. 2 mature ewes were given implants on 13 May (Group E, N = 10) or 18 July (Group L, N = 10) or received empty implants (Group C, N = 10) on one of these two dates. Blood samples were taken twice weekly for progesterone assay. In Exp. 1 the mean age (+/- s.e.m.) at puberty (progesterone greater than 2 nmol/l for two consecutive samples) was 35.4 +/- 0.8 weeks. Puberty was advanced by 5.2 weeks in Group L lambs, occurring at a mean age of 30.2 +/- 0.7 weeks (P less than 0.001). In Group E lambs the timing of puberty was unaltered, occurring at a mean age of 34.8 +/- 0.6 weeks. Mature ewes in Group L (Exp. 2) showed increased incidence of ovarian activity (9/10 ewes cycling by 26 September) compared with the control ewes (1/10) (P less than 0.001), but there was no effect in Group E ewes (3/10). The results demonstrate that continuous melatonin administration to adult and prepubertal ewes can mimic the effect of short days in terms of the reproductive response, and that the present and previous exposure to melatonin is critical in determining the response.     

Effects of shortened daylength and melatonin treatment on plasma prolactin and melatonin levels in pinealectomised and sham-operated ewes

Comparisons have been made between the effects of shortened daylength and melatonin treatment on plasma prolactin and melatonin levels in pinealectomised (Px) and sham-operated (Sh) ewes. Twenty-two anoestrous Merino crossbred ewes, maintained under normal grazing conditions, were assigned to four groups for a period of 9 weeks. Group 1 remained untreated (control), Group 2 was herded into a dark shed at 1600 h each day until dark (approx 4 h), ewes in Group 3 were injected with 100 μg melatonin s.c. at 1600 h each day and ewes in Group 4 were implanted with a melatonin capsule releasing 125–200 μg/day. Another group (Group 5) of 4 Px and 4 Sh ewes from the same flock was maintained in an animal house and subjected to shortened daylength (10. 5 h L : 13. 5 h D, lights off 1600 h). Three weeks after the treatments began, ewes in Groups 1–4 were exposed to a fertile ram and ewes in Group 5 to a vasectomised ram and the day of mating noted. No differences were evident between Groups 1–4 in the ewes' response to the ram, time taken to conceive, duration of gestation or number of lambs born. In untreated Px ewes no plasma melatonin (< 20 pg/ml) was found in either day or night samples, whereas intact animals showed the characteristic night-time rise. The silastic implants produced stable daytime blood levels of 90–120 pg/ml, whereas a single injection of 100 μg melatonin caused a transitory (2–3 h) rise. Shortened daylength (Group 2) or a single daily injection of melatonin (Group 3) lowered prolactin levels but only in ewes with an intact pineal gland, whereas melatonin implants (Group 4) caused a reduction in plasma prolactin in both Px and Sh sheep. The results indicate that light-induced alterations in prolactin production in sheep involve both the pineal gland and melatonin. Continuous melatonin release from implants caused changes in plasma prolactin levels similar to those seen following exposure to short days.     

Pituitary response to LHRH, LH pulsatility and plasma melatonin and prolactin changes in ewe lambs treated with melatonin implants to delay puberty

Prepubertal ewe lambs were treated with empty or filled melatonin implants. The implants were placed s.c. at birth and pituitary responsiveness to various doses of LHRH, LH/FSH pulsatility and prolactin and melatonin secretion were examined at 10, 19, 28, 36 and 45 weeks of age. Control animals (N = 10) showed no consistent alteration in pituitary responsiveness to LHRH during development. Ewes treated with melatonin (N = 10) had puberty onset delayed by 4 weeks (P less than 0.03) but no effect of melatonin on LH or FSH response to LHRH injection was observed at any stage of development. In the control and melatonin-treated ewe lambs the responses to LHRH injection were lower during darkness than during the day at all stages of development. No consistent differences in LH or FSH pulsatility were observed between treatment groups or during development. Prolactin concentrations, however, failed to decrease at the time of puberty (autumn) in the melatonin-treated group. Melatonin-treated ewe lambs maintained normal rhythmic melatonin production which was superimposed on a higher basal concentration and showed the same increase in melatonin output with age as the control ewes. These results indicate that the delayed puberty caused by melatonin implants is not due to decreased pituitary responsiveness to LHRH or to dramatic changes in basal LH or FSH secretion.     

Effects of melatonin implants in pony mares. 2. Long-term effects

The effects of melatonin implant treatment over a 4 wk period at the summer solstice on the transition into and out of the following anovulatory season were evaluated in ovary-intact and ovariectomized mares. Melatonin implants tended to delay the timing of the final ovulation of the breeding season (P = 0.0797) in the ovary-intact mares. Although the decline in LH secretion associated with the end of the breeding season was parallel between treatments and ovarian statuses, the rate of LH secretion, as expressed by its mathematical accumulation, was lower in ovariectomized, melatonin-treated mares than in ovariectomized, control mares suggesting that melatonin administration advanced the offset of the breeding season in ovariectomized mares (P = 0.0001). The first ovulation of the subsequent breeding season was significantly delayed in the melatonin-treated mares as compared with that of control mares (P = 0.0031). During reproductive recrudescence, the time of the onset of the increase in LH secretion was similar among all 4 groups but the patterns of LH secretion were different for each treatment and ovarian status combination (P = 0.0112). Mares with melatonin implants had a slower rate of increase in LH secretion than control mares (P = 0.0001), and ovariectomized mares had a faster rate of LH increase than intact mares (P = 0.0001). These results suggest that melatonin implants during the summer solstice can alter the annual reproductive rhythm in mares and support the concept that endocrine patterns of reproductive recrudescence are not entirely independent of the ovary.     

Initiation of the breeding season in ewe lambs and goat kids with melatonin implants

Sixty-eight female and 4 male lambs of the Chios breed born in autumn (September–October) and 48 female and 4 male kids of the Damascus breed also born in autumn (November), were used to evaluate the effect of melatonin implants (Regulin^®) on the initiation of the breeding season. For each species and sex, half of the animals were either left untreated to serve as controls (C) or received ear implants (females one and males two implants) of melatonin (MEL) in May (spring). Each C and MEL group of females was kept separately and away from males for 5 weeks after implantation and then, C and MEL males were joined with the respective groups for 45 (sheep) and 35 days (goats). Animals not conceiving during the early June–July breeding season, were mated again in September (natural breeding season). The reproductive performance and the 60-day milk yield of animals giving birth during the two seasons were compared. Early in the season (mid November–December), significantly more MEL than C ewes and goats gave birth (75.5% versus 23.5%, p < 0.01; 70.8% versus 37.5%, p < 0.05, respectively). For both species, most of the other characteristics examined were significantly affected by season, but not by treatment. Females giving birth early in the season were approximately 80 days younger at parturition and recorded a lower body weight at mating than those giving birth in the natural February–March season. In the first mating period, the animals mated and conceived had similar body weights to those not mated. The natural, compared with the early June–July mating season, was associated in sheep with higher litter weight at birth (7.0 kg versus 5.8 kg, p < 0.05) and in sheep and goats with a higher number (p < 0.05) of offspring born live (1.78 versus 1.38; 2.0 versus 1.61, respectively) and weaned (1.74 versus 1.36; 1.82 versus 1.35, respectively). Total litter size at birth and 60-day milk yield after weaning, were not significantly different between the two seasons. It could be concluded that melatonin implants administered during the last month of spring in autumn-born female Chios sheep and Damascus goats, advanced the initiation of their breeding season by about 80 days when joined with young males also treated with melatonin implants. The overall reproductive performance and milk yield of animals breeding early, was satisfactory and comparable to that of animals breeding in the natural breeding season.     

Melatonin-improved reproductive performance in sheep bred out of season

The effects of melatonin implants on out-of-season breeding in New Zealand Romney composite ewes, was determined by comparison of reproductive performance in ewes treated with progesterone+equine chorionic gonadotrophin (eCG) (control; n=107), melatonin+progesterone+eCG (n=97) or melatonin+progesterone (n=96). Conception rates in melatonin+progesterone+eCG-treated ewes (67%) were higher than in the control ewes (P<0.01; 47%). Pregnancy rates were higher in melatonin+progesterone+eCG-treated ewes (55%; P<0.001) compared with the control ewes (40%). Fewer melatonin+progesterone-treated ewes displayed oestrus (14%; P<0.001) and subsequently became pregnant (6%). Oestrus rates in melatonin+progesterone-treated ewes (14%) were lower than both the melatonin+progesterone+eCG-treated (82%) and control ewes (86%; P<0.001), which were similar to each other. The number of foetuses per pregnant ewe was similar in all three treatment groups. Serum melatonin concentrations at Day -9 were higher in the ewes treated with melatonin and there was a large variation between individual ewes, but concentrations were similar for pregnant and nonpregnant ewes. The combination of higher conception rate and the trend for more lambs per pregnant ewes resulted in more lambs being born per ewe treated in melatonin+progesterone+eCG-treated ewes compared to the other two treatment groups. These results suggest that melatonin implants, in conjunction with administration of progesterone and eCG, may be suitable as a means of increasing the number of lambs born per ewe treated in an out-of-season breeding program in New Zealand sheep flocks while melatonin and progesterone is not.     

雄性麋鹿的交配机会、社会等级和皮质醇水平

我们在北京麋鹿苑研究了发情期雄性麋鹿的社会行为、社会等级和血清皮质醇水平,并分析了三者间的相互关系。按照雄性麋鹿的行为,将雄性麋鹿分为优势群和从属群。优势群包括群主和挑战者,从属群包括单身汉和被淘汰群主。使用SJ—Ⅰ型事件记录器进行常规行为取样,用放射免疫分析法测定血清皮质醇含量。发现：(1)优势雄鹿的发情行为频次明显高于从属雄鹿;(2)攻击行为的发生频次在两组间无显著差异;(3)血清皮质醇含量在两组间也无显著差异。由此我们认为,发情期雄性麋鹿的社会等级序位影响许多行为的表达,优势雄鹿成功交配的机会比从属雄鹿多。而攻击行为和肾上腺皮质醇的分泌与社群等级无明显相关,可能是麋鹿在圈养状态下的一种适应策略,这将有利于缓解发情期雄鹿的紧张,从而允许更多的能量投放在发情交配上。     

Highly synchronous and fertile reproductive activity induced by the male effect during deep anoestrus in lactating goats subjected to treatment with artificially long days followed by a natural photoperiod

The response to the male effect was studied in two flocks of Saanen and three of Alpine goats during deep anoestrus in three consecutive years. Males and females were subjected to artificially long days for about 3 months (between December 4 and April 1) followed by a natural photoperiod. Bucks joined goats 42-63 days after the end of the long days treatment (between April 20 and June 3) and fertilisation was ensured by natural mating. In experiment 1 (n=248), female goats were treated or untreated with melatonin at the end of the long days treatment and treated or untreated for 11 days with fluorogestone acetate (FGA) before teasing. The males received melatonin implants. In experiment 2 (n=337), the factor studied was the association or non-association of the 11-day FGA treatment. Neither males nor females received melatonin implants. In experiment 3 (n=180), goats were treated for 11 days with FGA or with natural progesterone (CIDR). Neither males nor females received melatonin implants. In experiment 1, among the non-cycling goats (n=218), 99% ovulated and 81% kidded at 161+/-8 days after joining. Ninety-two percent of FGA-treated goats displayed an LH surge at 65+/-11h after teasing. Melatonin treatment did not affect any parameter but FGA advanced the kidding date. In experiment 2, 94% of the goats ovulated and 87% kidded. A major peak of conception was observed on days 3 and 8 after joining in FGA-treated and untreated goats, respectively. Among the FGA-treated goats, 83% displayed an LH surge. Over all flocks, most of the LH surges occurred over a 24-36 h interval, but the surge was initiated at different times in different flocks (36, 48 or 60 h after joining). FGA treatment did not influence the results, except for advancement of births of about 5 days. Differences among flocks were highly significant. In experiment 3, 94% of the goats displayed the LH surge, 93% ovulated and 68% kidded. Significant differences were found among flocks, but not between the FGA and CIDR groups. Bucks marked 85% of the goats 24-72 h after joining. The time interval between the detection of marked goats and detection of the LH surge depended on the time of marking (r=-0.62; p<0.05). In conclusion, treatment of both males and females goats with artificially long days followed by a natural photoperiod is very effective in inducing highly synchronous and fertile reproductive activity via the male effect in the middle of seasonal anoestrus.