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In seasonally anestrous goat does, ovulations can be induced by combining a treatment regimen including progestagen, eCG and prostaglandins. Nonetheless, ovulations occur only once and then does return to a seasonally anestrous state. This study was performed to determine whether the presence of a sexually active buck can stimulate a second ovulation after induced luteolysis using prostaglandins following the first ovulation. Three groups of seasonally anestrous does were treated to induce ovulations using an intra-vaginally inserted sponge containing a progestin combined with eCG and prostaglandin administrations. Goats that had ovulations were treated with a prostaglandin 11 days after progestin sponge removal. After the prostaglandin injection, does continued to be isolated from bucks (n = 8), were penned with a control buck (n = 9), or were penned with a sexually active buck (n = 10). The proportion of goats having ovulations after imposing the ovulation-induction protocol was greater than 80% and did not differ among treatment groups (P >  0.05). The proportion of does having ovulations after injecting prostaglandins was greater when does were penned with a sexually active buck (8/10) than does penned with a control buck (0/9) or that were isolated from bucks (0/8; P < 0.05). It is concluded that in seasonally anestrous goat does induced to have ovulations using a hormonal treatment regimen, the presence of a sexually active buck can induce a second ovulation when there is an induced luteolysis., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The effect of the continuous presence of sexually active Rasa Aragonesa rams on the plasma luteinizing-hormone (LH) concentrations of ewes was studied from November to May. Light-treated rams were rendered sexually active (SA rams) by exposure to 2 months of artificially long days (16 h light/8 h dark) in one of two groups from either 1 November (SAR1, n = 3) or 1 December (SAR2, n = 3). Rams (n = 6) in a Control group were kept under the natural photoperiod. Thirty ewes were ovariectomized in September and implanted with a subcutaneous implant (l = 15 mm) that contained estradiol-17β. One group of ewes (SAR; n = 10) was housed with control rams from 1 October to 15 February before being housed with SAR1 rams from 16 February to 31 March, and with SAR2 rams from 1 April to 31 May. A second group of ewes (C; n = 10) remained with control rams throughout the experiment, and a third group was kept isolated from rams throughout the experiment (ISO; n = 10). Blood samples were collected weekly from November to May, and plasma LH concentrations were measured. In the breeding season (November-February), plasma LH concentrations of ewes did not differ significantly between groups (SAR: 2.00 ± 0.34; C: 1.88 ± 0.16; ISO: 1.67 ± 0.51 ng/ml). From March to May (seasonal anestrus), however, LH plasma concentrations decreased in the C and ISO groups (1.30 ± 0.20 and 0.48 ± 0.04 ng/ml, respectively), but remained at the same level as in the breeding season in the SAR group (2.30 ± 0.17 ng/ml; P < 0.001). Significant differences (P < 0.01) between groups were observed from March onwards: LH concentrations were highest in SAR ewes (P < 0.001) and lowest in the ISO ewes. In conclusion, the continuous presence of sexually active rams prevented the seasonal decrease in plasma LH concentrations, probably by preventing the seasonal negative feedback of estradiol on LH secretion., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The exposure of adult, female, Mediterranean goats during anoestrus to males with induced sexual activity via photostimulation, induces a very high percentage of ovulations. The present work examines the ability of photostimulated bucks to improve the male effect-induced reproductive response of young does over that induced by non-stimulated bucks. A 2×2 factorial experiment was designed, consisting of doe age and buck photoperiod treatments. During seasonal anoestrus, 41 does aged 7 (n=19) or 10 (n=22) months were subjected to the male effect on 10 April; half of each group was exposed to males rendered sexually active by prior exposure to 3 months of long days (16 h of light/day) from 31 October (PHOTO bucks), and half to males maintained under the natural photoperiod (CONTROL bucks). Oestrous activity was recorded daily by direct visual observation of the marks left by male-worn marking harnesses over the 32 days following the bringing of the sexes together (introduction). Doe body weight and body condition were determined weekly. Ovulation was detected by measuring plasma progesterone concentrations twice per week over the 3 weeks after introduction. The ovulation rate was assessed by transrectal ultrasonography. Fecundity, fertility, prolificacy and productivity were also determined. The interaction doe age × buck photoperiod treatment had no effect on any outcome. The percentage of females showing ovulation or oestrus was higher in the does exposed to PHOTO bucks (85% v. 43% for those exposed to CONTROL bucks) they also showed higher fertility (75% v. 43%) and productivity (1.05±0.17 v. 0.57±0.16 kids born per doe serviced) (all P values at least P&lt;0.05). The 10-month-old group showed higher percentage of females showing ovulation, oestrus, fertility and productivity than the 7-month-old does after the male effect (females showing ovulation: 82% v. 42%; showing oestrus: 73% v. 42%; fertility: 73% v. 42% and productivity: 1.09±0.17 v. 0.47±0.14 goat kids born per doe serviced; respectively, all P values at least P&lt;0.05). The present results show that the use of photostimulated males improves the reproductive performance of 7- and 10-month-old does, and may contribute towards increasing their productivity and lifetime reproductive performance.

Goats are seasonal breeders with the main cue controlling the timing of breeding season being photoperiod. Hence, the season of birth impacts puberty onset: spring-born goats reach puberty in autumn, at 7 mo of age, whereas autumn-born goats reach puberty at 1 yr during the next reproductive season. The aim of this study was to determine whether exposure of autumn-born young females to sexually active males could counteract the delay in puberty onset observed in autumn-born goats. Females exposed to sexually active males (n = 8) reached puberty earlier than isolated females (n = 8), with exposed females ovulating at a mean age of 3.5 mo. To our knowledge, such precocious puberty onset obtained through social stimulation has never been described in the literature. Moreover, those exposed females exhibited estrus behavior for most ovulations. Our results indicate that in goats born out of season, exposure to sexually active bucks is a really efficient approach to induce early puberty, suggesting that social interactions could have a crucial impact on the regulation of pubertal transition., (Copyright © 2019 Elsevier Inc. All rights reserved.)

We showed previously that the permanent presence of bucks rendered sexually active by photoperiodic treatments, thereafter called photostimulated bucks, prevents the occurrence of seasonal anovulation; also, the introduction of these sexually active bucks induces ovulations during seasonal anestrus. Here, we studied the response of ovariectomized goats bearing 12-mm subcutaneous implants filled or not with estradiol to sexually active males to determine (1) whether the permanent presence of such bucks prevents the decrease of LH despite the presence of a negative feedback by estradiol mimicking that of seasonal anestrus (experiment 1) and (2) whether the introduction of photostimulated bucks increases the plasma LH concentrations in spite of this negative feedback (experiment 2). In experiment 1, one group of goats remained in contact with sexually active bucks, whereas the other group remained in contact with control bucks. Plasma LH concentrations were high and did not differ with time or between groups of females from November to February (P > 0.05), when both types of bucks were sexually active. Afterward, in goats in contact with control and sexually inactive bucks, LH concentrations decreased from March (P ≤ 0.01) and remained low until May, whereas LH levels remained high from March to May in goats in contact with the photostimulated bucks (P > 0.05). In experiment 2, 2 groups of females bearing empty subcutaneous implants, and 2 groups of goats bearing subcutaneous implants filled with estradiol, were exposed to control or photostimulated bucks. Plasma LH concentrations did not increase in goats bearing empty implants, when exposed to control or photostimulated bucks (from 2.01 ± 0.26 to 1.98 ± 0.31 ng/mL, and from 2.45 ± 0.29 to 2.42 ± 0.21 ng/mL respectively; P > 0.05). In contrast, plasma LH concentrations increased from 0.97 ± 0.41 to 2.80 ± 0.62 ng/mL in goats exposed to the photostimulated bucks and bearing estradiol implants (P < 0.05). Thus, the permanent presence of sexually active bucks prevented the decrease of plasma LH concentration in OVX + E2 goats during the seasonal anestrus, and the introduction of the photostimulated bucks increased the plasma LH concentrations in OVX + E2 goats during the seasonal anestrus. Therefore, we conclude that in both cases, the photostimulated bucks are able to reduce or counterbalance the seasonal negative feedback of estradiol on LH secretion., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The present experiment was conducted to determine (1) whether the sexually active bucks are able to stimulate the ovulatory activity of seasonal anestrous goats when the daily contact is reduced to 15 min/day during 15 days and (2) the exact ovulatory activity in anestrous goats exposed to bucks for 2 hours or less per day during 15 days. One group of goats (n = 15) was isolated from bucks. The other six groups (n = 15 each) were exposed to sexually active bucks (n = 1 each) for 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, or 24 hours during 15 days. Goats with plasma concentrations of progesterone greater than 0.5 ng/mL were considered to have ovulated. More than 93% of females exposed to bucks ovulated throughout the experiment regardless of the duration of contact with males, whereas none of them ovulated in the isolated group (P < 0.0001). The proportions of females that ovulated at least once did not differ among groups as well as the proportions of goats that displayed normal or short ovulatory cycles. The interval between the introduction of males and the first ovulation did not differ among groups of goats in contact with bucks for 15 minutes, 30 minutes, 1 hour, or 2 hours. However, in these groups, this ovulation occurred about 2 days later than in females in contact with males during 4 or 24 hours (6.3 vs. 4.4 days; P < 0.05). We conclude that 15 minutes of daily contact with sexually active buck is sufficient to stimulate the ovulatory activity in seasonally anestrous goats, but the first ovulation is delayed in goats exposed to males for 2 h/day or less during 15 days in comparison with those in contact with males for 4 or 24 h/day., (Copyright © 2016 Elsevier Inc. All rights reserved.)

A well-defined season of sexual rest controlled by photoperiod is observed in female sheep and goats during spring and summer, delineating their "anestrous season"; bucks also decrease sexual activity at about the same time. Nutrition and/or socio-sexual stimuli play only secondary roles. However, the presence of sexually active males can reduce the length of seasonal anestrus. Whether it can also completely suppress anestrus has not been investigated. Here we tested this in goats in 3 experiments, using bucks rendered sexually active out of season by exposure to long days. The continuous presence of these males prevented goats to display seasonal anestrus: 12/14 females cycled the year round, vs. 0/13 and 0/11 for females with un-treated bucks or without bucks (experiment 1). When active bucks were removed, females immediately entered anestrus (7/7 stopped ovulating vs. 1/7 if maintained with active bucks; experiment 2). Finally, 7/7 anestrous does with bucks in sexual rest since 1.5months commenced cycling rapidly during mid-anestrous, when these bucks became sexually active following a treatment with artificial long days, vs. 0/7 with un-treated bucks or no bucks (experiment 3). The presence/withdrawal of active bucks had a highly significant effect in the three experiments (P≤0.002). Therefore, the presence of a mating opportunity can completely override the photoperiodic inhibition of reproduction of females throughout the anestrous season. Results suggest that we must re-evaluate the relative contributions of photoperiod vs. other external cues in controlling seasonal reproduction, thus offering new non-pharmaceutical ways for controlling out-of-season reproduction in small ruminants., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The response of male goats exposed to different durations of long days (LD) during an extra-light treatment in autumn-winter, and their ability to induce ovulations in seasonally anovulatory goats were investigated in 2 experiments. In experiment 1, control males were exposed to natural photoperiod (n = 5), whereas 4 additional groups (n = 5/group) were exposed to 16 h of light per d during 75, 45, 30, or 15 d of LD. In the 4 groups, photoperiodic treatments ended on January 15th. Plasma concentrations of testosterone were determined in blood samples obtained once a week from October 15th to May 30th. The rise of testosterone levels occurred earlier in males from the 75-LD and 45-LD groups than in those from the 30-LD, 15-LD, and control groups (P < 0.05). In addition, the time during which levels of testosterone remained >5 ng/mL was longer in males from the 75-LD and 45-LD than in those from the 30-LD and 15-LD groups (P < 0.05). In experiment 2, a group of anovulatory goats (n = 13) was isolated from males, while 3 additional groups were put in contact during 15 d with males previously exposed to 75, 45, or 30 days of LD (n = 25, 27, and 26 females/group, respectively and n = 3 males per group). The proportion of goats that ovulated was higher in the 3 groups in contact with the photo-stimulated males (range: 88%-92%) than in the group isolated from them (0%; P < 0.05). The proportion of pregnant females did not differ between the 3 groups of does in contact with photo-stimulated males (range: 78%-92%; P > 0.05). We conclude that, in our experimental conditions, a photoperiodic treatment as short as 30 d of LD during autumn-winter, stimulated testosterone secretion of bucks during their period of sexual rest and rendered them able to induce ovulations in seasonal anestrous goats and to obtain pregnancies in these females., (Copyright © 2014 Elsevier Inc. All rights reserved.)

In seasonal breeding species, the gene encoding for the melatonin MT(1) receptor (oMT(1)) is highly polymorphic and numerous data have reported the existence of an association between an allele of the receptor and a marked expression of the seasonality of reproduction in ewes. This allele called "m" (previously named "-" allele) carries a mutation leading to the absence of a MnlI restriction site as opposed to the "M" allele (previously named "+" allele) carrying the MnlI restriction site (previously "+" allele). This allows the determination of the three genotypes "M/M" (+/+), "M/m" (+/-) and "m/m" (-/-). This mutation is conservative and could therefore not be causal. However, it is associated with another mutation introducing the change of a valine to an isoleucine in the fifth transmembrane domain of the receptor. Homozygous "M/M" and "m/m" animals consequently express structurally different receptors respectively named oMT(1) Val(220) and oMT(1) Ile(220). The objective of this study was to test whether these polymorphic variants are functionally different. To achieve this goal, we characterized the binding properties and the transduction pathways associated with both variants of the receptors. Using a pharmacological approach, no variation in binding parameters between the two receptors when transiently expressed in COS-7. In stably transfected HEK293 cells, significant differences were detected in the inhibition of cAMP production whereas receptors internalization processes were not different. In conclusion, the possibility that subtle alterations induced by the non conservative mutation in "m/m" animals might modify the perception of the melatoninergic signal is discussed in the context of melatonin action., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Goats and sheep generally express seasonal variations in their sexual behaviour, spermatogenic activity (from moderate decrease to very low sperm production), gamete quality (variations in fertilization rates and embryo survival), ovulation frequency (presence or absence of ovulation), and ovulation rate (number of eggs shed per ovulation period). This induces seasonal availability of derived, fresh animal products (meat, milk and cheese) because of a more or less marked seasonal distribution of births. A complex combination of an endogenous circannual rhythm driven and synchronized by light and melatonin, which controls the pulsatile activity of GnRH neurons in the preoptic-mediobasal hypothalamus, is responsible for these changes. Dramatic and long-term neuroendocrine changes, involving different neuromediator systems and neuronal plasticity, have been shown to play a role in these processes. A strong variability between breeds exists in both species regarding the dates of onset and end of the breeding season, with a gradient of seasonality from southern to northern latitudes. Within a breed, seasonal traits are heritable; thus, genetic selection could be one way to decrease seasonality in sheep and goats in the future., (© 2010 Blackwell Verlag GmbH.)

The present study examines the ovulatory activity of wild and domesticated ewes subjected to either a constant photoperiod of long days (16L:8D) or natural changes in daily photoperiod for 16 mo. The aim was to determine whether an endogenous reproductive rhythm controls seasonal reproductive activity in these sheep, and how the photoperiod might affect this. The effects of long-day photoperiods on long-term changes in prolactin and melatonin secretion were also evaluated. The two species showed changes in reproductive activity under the constant photoperiod conditions, suggesting the existence of an endogenous rhythm of reproduction. This rhythm was differently expressed in the two types of ewe (P < 0.05), with the domestic animals exhibiting much greater sensitivity to the effects of long days. A circannual rhythm of plasma prolactin concentration was also seen in both species and under both photoperiod conditions, although in both species the amplitude was always lower in the long-day animals (P < 0.01). The duration of the nocturnal melatonin plasma concentrations reflected the duration of darkness in both species and treatments. The peak melatonin concentration did not differ between seasons either under natural or long-day photoperiods.

The gene encoding the MT1 melatonin receptor in sheep has a restriction fragment length polymorphism (RFLP) site to the MnlI enzyme whose incidence is associated to the expression of seasonality in several breeds. The aim of this study was to examine the relationship between this genetic marker and the physiological effects of MT1 receptor gene polymorphism on several seasonal functions in Ile-de-France ewes. The study was performed using 12 pairs of half-sib adult Ile-de-France ewes. Within each pair, ewes were selected on the basis of their genotype at the MnlI RFLP site: group +/+ and -/- (presence and absence of MnlI restriction site, respectively). No difference in the dates of the beginning, the end or the length of the breeding season was observed between groups during the two-year study. The seasonal changes in prolactin secretion were not different between groups. Similarly, wool growth rate and primary follicle activity, measured for one year, varied with the time of the year in the same way in the two groups. Our study therefore failed to show any relationship between MT1 polymorphism and reproductive seasonality in Ile-de-France ewes. This suggests that the influence of this polymorphism on the regulation of seasonal function is dependent upon the breed and/or environmental conditions. The MT1 polymorphism can explain only a small part of the genetic variability of seasonal functions and the implication of other genes must be investigated.

Background: Seasonality of ovulatory activity is observed in European sheep and goat breeds, whereas tropical breeds show almost continuous ovulatory activity. It is not known if these tropical breeds are sensitive or not to temperate photoperiod. This study was therefore designed to determine whether tropical Creole goats and Black-Belly ewes are sensitive to temperate photoperiod. Two groups of adult females in each species, either progeny or directly born from imported embryos, were used and maintained in light-proof rooms under simulated temperate (8 to 16 h of light per day) or tropical (11 - 13 h) photoperiods. Ovulatory activity was determined by blood progesterone assays for more than two years. The experiment lasted 33 months in goats and 25 months in ewes., Results: Marked seasonality of ovulatory activity appeared in the temperate group of Creole female goats. The percentage of female goats experiencing at least one ovulation per month dramatically decreased from May to September for the three years (0%, 27% and 0%, respectively). Tropical female goats demonstrated much less seasonality, as the percentage of goats experiencing at least one ovulation per month never went below 56%. These differences were significant. Both groups of temperate and tropical Black-Belly ewes experienced a marked seasonality in their ovulatory activity, with only a slightly significant difference between groups. The percentage of ewes experiencing at least one ovulation per month dropped dramatically in April and rose again in August (tropical ewes) or September (temperate ewes). The percentage of ewes experiencing at least one ovulation per month never went below 8% and 17% (for tropical and temperate ewes respectively) during the spring and summer months., Conclusions: An important seasonality in ovulatory activity of tropical Creole goats was observed when females were exposed to a simulated temperate photoperiod. An unexpected finding was that Black-Belly ewes and, to a lesser extent, Creole goats exposed to a simulated tropical photoperiod also showed seasonality in their ovulatory activity. Such results indicate that both species are capable of showing seasonality under the photoperiodic changes of the temperate zone even though they do not originate from these regions.

The seasonality of testicular volume and sexual behavior in two Greek breeds of sheep, Chios and Serres, was studied using 10 mature rams of each breed. The rams were kept out of breeding during 2 consecutive years. Live weight was recorded at monthly intervals. Testicular volume was measured at 2-week intervals using an orchidometer. Sexual behavior was recorded at 4-week intervals by exposing rams to oestradiol-treated ovariectomized ewes. The total number of mounts and matings, and the reaction time to first mount and mating were recorded. Chios rams were heavier than Serres rams (87.4 +/- 2.0 kg versus 76.4 +/- 1.9 kg, respectively). All traits varied significantly with month but only testicular volume exhibited a clear seasonal trend in both breeds, with a maximum volume in July-August and a minimum in February-April. Number of mounts showed clear seasonal trend in the Chios breed, with maximum in November. Number of mounts was significantly correlated with length of daylight (-0.18 and -0.21 for Chios and Serres, respectively; P < 0.01) and relative humidity (0.14 and 0.17 for Chios and Serres, respectively; P < 0.05). Testicular volume was positively correlated with air temperature (0.28; P < 0.01) and relative humidity (-0.23; P < 0.01) in the Serres breed only. Results of this study suggest that the testicular volume and number of mounts exhibit seasonal variation in the Chios and Serres rams.

We investigated if absolute (nocturnal) or relative (nocturnal/diurnal ratio) plasma melatonin concentrations were associated with the seasonal ovulatory activity in Ile-de-France ewes. Ninety-six and 121 ewes in two different groups of the same flock were used to determine the potential existence of a relationship between melatonin concentrations at the summer and winter solstices, and the dates of onset and offset of the ovulatory activity, respectively. The dates of the first and last ovulations were estimated by assaying progesterone in plasma samples taken once weekly. Mean +/- SEM (1) plasma melatonin concentrations at the summer solstice and at the winter solstice were 302.4 +/- 19.4 and 412.0 +/- 18.7 pg x mL(-1), respectively, (2) date of onset of the breeding season 29 Jul. +/- 1.6 days, (3) date of offset of the breeding season 24 Jan. +/- 2.2 days. In spite of a large variability in the different traits studied here, the analyses of correlation and regression indicated that neither the absolute nor relative melatonin concentrations were significantly related with the dates of onset or offset of ovulatory activity. Therefore, we concluded that absolute or relative plasma melatonin concentrations are not linked to the seasonal breeding activity, in Ile-de-France ewes.

Background: We wanted to determine if changes in the expression of serotonin 2A receptor (5HT2A receptor) gene in the premammillary hypothalamus are associated with changes in reproductive neuroendocrine status. Thus, we compared 2 groups of ovariectomized-estradiol-treated ewes that expressed high vs low LH pulsatility in two different paradigms (2 groups per paradigm): (a) refractoriness (low LH secretion) or not (high LH secretion) to short days in pineal-intact Ile-de-France ewes (RSD) and (b) endogenous circannual rhythm (ECR) in free-running pinealectomized Suffolk ewes in the active or inactive stage of their reproductive rhythm., Results: In RSD ewes, density of 5HT2A receptor mRNA (by in situ hybridization) was significantly higher in the high LH group (25.3 +/- 1.4 vs 21.4 +/- 1.5 grains/neuron, P < 0.05) and 3H-Ketanserin binding (a specific radioligand) of the median part of the premammillary hypothalamus tended to be higher in the high group (29.1 +/- 4.0 vs 24.6 +/- 4.2 fmol/mg tissu-equivalent; P < 0.10). In ECR ewes, density of 5HT2A receptor mRNA and 3H-Ketanserin binding were both significantly higher in the high LH group (20.8 +/- 1.6 vs 17.0 +/- 1.5 grains/neuron, P < 0.01, and 19.7 +/- 5.0 vs 7.4 +/- 3.4 fmol/mg tissu-equivalent; P < 0.05, respectively)., Conclusions: We conclude that these higher 5HT2A receptor gene expression and binding activity of 5HT2A receptor in the premammillary hypothalamus are associated with stimulation of LH pulsatility expressed before the development of refractoriness to short days and prior to the decline of reproductive neuroendocrine activity during expression of the endogenous circannual rhythm.

Melatonin, which is synthesized at night by the pineal gland, is present in the cerebrospinal fluid (CSF), but its entry site and its role in this compartment are not known. Using several approaches, we tested the hypothesis that melatonin enters the CSF through the pineal recess, an evagination of the third ventricle. CSF melatonin concentrations are higher near the pineal gland than in the anterior part of the third ventricle, and decrease markedly (80%) after sealing off the pineal recess. Moreover, ultrastructure and permeability analyses of the pineal-CSF interface showed that melatonin could reach the CSF either via delivery in situ by protruding pinealocytes that make direct contact with the CSF or via extracellular secretion and interstitial fluid draining into the ventricular lumen. These data indicate that melatonin in the CSF probably originates from a few pinealocytes of the basal part of the pineal gland neighbouring the pineal recess. Melatonin carried to the brain by the blood appears to be able to mediate the effects of photoperiod on reproduction, but it is unclear whether melatonin in CSF may fine-tune this response both in terms of timing and amplitude. It is critical to determine which pathway, blood or CSF, allows melatonin to reach its central targets more efficiently.

A study was conducted in subtropical northern Mexico (26 degrees N) to determine whether the presence of estrous females can improve the response of seasonally anovulatory goats to the introduction of bucks in the group. The induction of estrous activity was studied in three groups of anovulatory lactating goats during seasonal anestrus. These females were of the Mexican Creole breed. In the control group (sexually inactive (SI), n = 20), two control (SI) bucks exposed to normal seasonal daylength variations were used. In the second group (SI + E, n = 20 + 3), two control males were also used, but in addition, three females of the group were in estrus at the time of male introduction. In the third group (sexually active, SA + E, n = 19 + 4), anovulatory females were exposed to two bucks made sexually active by exposure to 2.5 months of long days (16L:8D) followed by two subcutaneous 18 mg melatonin implants, and four estrous females were also present when introducing the bucks. In all groups, males were introduced on 15 March and estrous detection was conducted twice daily for 15 days. The sexual activity of the bucks was observed from 08:00 to 10:00 h during the first five days of exposure to females. More females displayed estrous behavior in the first 15 days following the introduction of the males in the SA + E group (18/19) as compared with the SI or SI + E groups (2/20 and 0/20, respectively; P < 0.001). No difference was observed between the two latter groups. Thirteen females of SA + E group showed a second estrus between days 6 and 11 (short estrous cycle duration: 5.4 +/- 0.4 days). By contrast, in the SI group none showed a second estrus. The sexual behavior of the males in the SA + E group was greater as compared with that of the males in SI and SI + E groups (over 80% of the total sexual activity recorded in the three groups; P < 0.001). By contrast, no differences were found between SI and SI + E males. These results indicate that the presence of estrous females alone at the time of buck introduction is not sufficient to induce an adequate stimulation of seasonally inactive males. The use of sexually active bucks is necessary to induce reproductive activity in anovulatory females, whereas preparation of the bucks with long days followed by melatonin implants allows them to gain such a capacity., (Copyright 2002 Elsevier Science B.V.)

Sheep in temperate latitudes are seasonal breeders. Of the different seasonal cues, photoperiod is the most reliable parameter and is used by animals as an indication of the time of the year to synchronize endogenous annual rhythms of reproduction and physiology. The photoperiodic information is transduced into neuroendocrine changes through variations in melatonin secretion from the pineal gland. Melatonin triggers variations in the secretion of luteinizing hormone-releasing hormone, luteinizing hormone and follicle stimulating hormone (LHRH/LH/FSH) responsible for seasonal changes in reproductive activity. In female sheep, the seasonal changes in the hormonal LH pattern mainly reflect an increase in the negative feedback exerted by estradiol under long days on the frequency of pulsatile LH secretion. The resulting seasonal inhibition of LH secretion involves the activation of monoaminergic and especially dopaminergic systems by estradiol. Other types of physiological regulation subject to seasonal changes such as voluntary food intake (VFI), fat metabolism, body mass and pelage growth also occur in sheep, goats or related wild species. Several neuroendocrine intermediates seem to be shared by these different systems and may participate in their synchronization, providing the advantage that this helps mammalian species to adapt to their environment.

The mechanisms by which melatonin controls seasonal reproduction are poorly understood. The use of a large animal model, namely the sheep, has allowed progress in the understanding of these mechanisms, and is the subject of this review. Firstly, the contribution made by large animal models to demonstrating that melatonin acts in the hypothalamus and the identification of this hypothalamic target is reviewed. Secondly, the way in which large animal models have facilitated the demonstration of a specific mechanism of release of melatonin in the cerebrospinal fluid and, thus, raised the question of the route used by melatonin to reach its central targets is discussed. Finally, the human and agricultural relevance of the data presented is considered.

To determine whether a link exists between reproductive seasonality and the structure of the gene for melatonin receptor Mel(1a), the latter was studied in two groups of Mérinos d'Arles (MA) ewes previously chosen for their genetic value, which took into account their own out-of-season ovulatory activity adjusted by environmental parameters and that of their relatives. The genomic DNA of 36 ewes found regularly cycling in spring (group H) and that of 35 ewes never cycling in spring (group L) during the 2-3 yr before the present study was prepared, and the cDNA corresponding to almost all exon II was amplified and checked for the presence of MnlI restriction sites. The presence (+) or absence (-) of an MnlI site at position 605 led to genotypes "++", "+-", and "--", whose frequencies differed significantly (P < 0.001) between the H and L groups: 52.8%, 47.2%, and 0% vs. 28.5%, 42.9%, and 28.5%, respectively. Sequencing of exon II cDNA in group L ewes with genotype -- showed the presence of only one allele - with 4 mutations, while that in ewes with genotype ++ showed different types of alleles unrelated to the H or L groups. These + alleles exhibited a combination of 1 to 7 of the 8 mutations recorded in the part of exon II studied. The genotyping of 29 ewes from the more seasonal Ile-de-France breed indicated that 38% of animals had a -- genotype and exhibited the same mutations as in the MA ewes. Finally, a comparison of (125)I-melatonin binding to membrane preparations of pars tuberalis showed a lower number of binding sites (P < 0. 0005) in MA ewes with genotype ++ than in those with genotype -- (43. 2 +/- 4.4 vs. 75.4 +/- 8.4 fmol/mg protein in genotype ++ and genotype --, respectively). In conclusion, the data show an association between genotype -- for site MnlI at position 605 and seasonal anovulatory activity in MA ewes.

The aim of this study was to determine if there is a seasonal pattern of sexual activity dependent on food availability in male Creole goats in subtropical Mexico. The study was conducted in the Laguna Region in the State of Coahuila, Mexico (26 degrees N). Male Creole goats (n = 8) were kept in a shed, fed alfalfa ad libitum and given 200 g of concentrate daily throughout the study. Live weight and testicular weight were determined every 2 wk. Sexual behavior and sperm production were determined monthly. Blood samples were obtained weekly to determine testosterone plasma concentrations. All variables were subjected to sinusoidal modeling procedures and showed important seasonal variations (P < 0.0001) with different phase angles for body weight, testicular weight and testosterone plasma concentrations. The nadir of live weight occurred in November and the peak in May. The lowest testicular weight (90 g) and testosterone plasma concentrations (0.1 ng/mL) were observed in January and February, respectively, while the peaks were observed in July and August (145 g and 10 ng/mL, respectively). Ejaculation latency also varied during the study, being low between May and November (96 sec) and reaching a peak in April (183 sec). Minimum number of spermatozoa per ejaculate occurred between February and April (1.4 x 10(9) cells/ejaculate) while the maximum number was observed between May and September (2.8 x 10(9) spermatozoa/ejaculate). Progressive sperm motility was low between January and April (3.04 on average) and high between May and November (about 3.55 on average). The percentage of live spermatozoa diminished between January and April (68% in April) and then increased to values around 80% between May and November. These results lead us to conclude that male Creole goats in Northern Mexico, fed constantly throughout the year, exhibit seasonality in their reproductive activity. Intense sexual activity occurred between May and December.

Many mammalian species from temperate latitudes exhibit seasonal variations in breeding activity which are controlled by the annual photoperiodic cycle. Photoperiodic information is conveyed through several neural relays from the retina to the pineal gland where the light signal is translated into a daily cycle of melatonin secretion: high at night, low in the day. The length of the nocturnal secretion of melatonin reflects the duration of the night and it regulates the pulsatile secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Changes in GnRH release induce corresponding changes in luteinising hormone secretion which are responsible for the alternating presence or absence of ovulation in the female, and varying sperm production in the male. It is not yet known where and how this pineal indoleamine acts to exert this effect. Although melatonin binding sites are preferentially localised in the pars tuberalis (PT) of the adenohypophysis, the hypothalamus contains the physiological target sites of melatonin for its action on reproduction. Melatonin does not seem to act directly on GnRH neurons; rather it appears to involve a complex neural circuit of interneurons that includes at least dopaminergic, serotoninergic and excitatory aminoacidergic neurons.

One hundred and sixty adult ewes of the Chios breed were divided randomly into two groups. One group was used for breeding in spring (S) and the other in autumn (A). In both groups oestrous behaviour was detected once a day. Ovulatory activity, 7 d after oestrus, fertility, prolificacy, embryo mortality, birth weight of lambs and milk production were recorded. The percentage of ewes which exhibited oestrous behaviour was 92 and 100% in S and A groups, respectively, while fertility of mated ewes was 98 and 100%. Ovulation rate was significantly lower in S than in A ewes (M +/- sd; 2.85 +/- 1.07 versus 3.44 +/- 1.45, respectively, P < 0.0001). However, prolificacy did not differ between the two groups (2.04 +/- 0.77 versus 2.13 +/- 0.85, for S and A ewes, respectively) as it did not increase after an ovulation rate of 4.0. There were no differences in birth weights (except for triplets) but total milk production was significantly higher in S ewes (257.5 +/- 100.7 kg versus 153.0 +/- 51.9 kg, for S and A, respectively, P < 0.001). These results suggest that despite a higher ovulation rate in autumn, higher embryonic mortality at this time of the year leads to equivalent fertility, prolificacy and birth weight in spring as in autumn.

The aim of this study was to determine whether season of birth and length of nursing affected the duration of postpartum anestrus in Creole female goats maintained on a constant plane of nutrition in subtropical Mexico. Three experiments were conducted in the Laguna region in the State of Coahuila, Mexico (26 degrees N). In the first experiment, 34 goats gave birth in January; in the second, 31 females gave birth in May; and in the third, 22 goats kidded in October. At parturition, females were allocated to 1 of 3 groups based on body weight and date of parturition: kids were weaned at 2, 30 or 90 d according to their group. After weaning, females were milked manually once a day until the end of the study. All animals were kept in a shed and were fed alfalfa ad libitum and given 200 g of concentrate daily. Starting 1 wk after parturition, estrous behavior was detected twice daily using an apron-bearing male, and blood samples were obtained twice weekly to determine ovarian activity from the plasma progesterone levels. A strong effect of month of parturition was found on the duration of postpartum anestrus (P < 0.0001), which was longer in females kidding in January (about 200 d) than in those kidding in May (about 100 d) or October (about 50 d). A tendency for an interaction between season of parturition and length of nursing was observed in the length of anovulation (P < 0.07): for parturition in October, anestrus was longer when kids were weaned after 90 d than after 2 or 30 d (P < 0.01). Season of parturition also affected dates of reinitiation of ovulatory and estrous activity (P < 0.001). Proportions of normal, short and long cycles and of associations between estrous and ovulations were not influenced by season of parturition or the age of weaning. These data demonstrate that in subtropical latitudes, season of parturition can dramatically influence the duration of postpartum anestrus independently of the availability of food.

The involvement of the uterus in early regression of corpora lutea induced by the ram effect was studied in seasonally anoestrous Barbarine ewes. In experiment 1, group I was only submitted to the male effect (control, n = 15) while group II (n = 14) was injected every 12 h with flunixin meglumine, a PGF2 alpha synthetase inhibitor (finadyne), from day 3 to day 6 (day 0: day of ram introduction). The preovulatory LH surge appeared at the same time (around 21 h after ram introduction) in both groups. Finadyne treatment significantly decreased 13-14-dihydro-15-keto-PGF2 alpha (PGFM) pulses (1.3 +/- 0.3 versus 0.4 +/- 0.2; P < 0.05), the number of short cycles (50 versus 14%, P < 0.05), and provided a single peak of oestrus, 15-16 days after the introduction of the rams, instead of between day 14 and day 23 (P < 0.01). In experiment 2, 17 hysterectomized ewes were allocated into two groups: group III (n = 8) was injected with oil and group IV (n = 9) received an intramuscular injection of 20 mg of progesterone immediately before introduction of rams. An additional group of intact ewes was used as control (group V, n = 9). Hysterectomy did not affect the ovulation response to the ram effect, but completely suppressed short cycles (0 versus 78%, P < 0.001). The preovulatory LH surge was delayed in hysterectomized females (36.0 +/- 14.1 versus 16.6 +/- 11.4 h; P < 0.004). Treatment with progesterone significantly (P < 0.01) increased the interval between introduction of rams and the preovulatory LH surge. In conclusion, suppression of short cycles by hysterectomy and an inhibitor of PGF2 alpha synthetase suggest that the uterus is essential for determining the lifespan of ram-induced corpora lutea and that premature release of PGF2 alpha is the cause of early luteal regression. The hypothesis that lower secretion of progesterone before D5 could be the initial cause of the premature induction of the luteolytic signal is discussed.

Annual variations in day length are responsible for seasonal changes in reproductive activity in sheep. However, in constant photoperiodic conditions, ewes express an endogenous rhythm characterized by alternations of reproductive activity and quiescence that are not synchronized among animals. Thus, the main role of photoperiod in the natural environment appears to be the synchronization of this endogenous rhythm. Photoperiodic information is processed through a complex nervous and endocrine pathway to modulate reproductive activity. Light information perceived at the level of the retina is transformed through neural processing into an endocrine signal by the pineal gland: the nocturnal increase in melatonin release. Recent studies strongly suggest that melatonin has a hypothalamic target to modulate the reproductive neuroendocrine axis. Most LHRH perikarya are located in the preoptic area, but this region is devoid of melatonin receptors, and microimplants of melatonin placed in the preoptic area do not effect LHRH release. Thus, melatonin influences LHRH neurones indirectly and must involve interneurons. Good evidence now exists to demonstrate that a population of dopaminergic neurons with axons projecting to the median eminence is one of these interneurons.

Melatonin, synthetized by the pineal gland, is the chemical messenger which allows seasonal animals to perceive day length changes. The nervous message, transformed into a hormonal one, triggers pulsatile activity of the LHRH neurons. Its sites and mode of actions are not completely elucidated. The most frequent mode of distribution is the sub-cutaneous implant, which induces an advance of the cyclical ovulatory activity of ewes and goats. The date of fertilization is advanced and fecundity of females is improved. It can be used alone, or in association with other hormonal treatments, or after an artificial photoperiodic treatment. Under these conditions, it allows a quantitative and qualitative increase in out-of-season sperm production in rams and he-goats.

Sheep are seasonal breeders, but a lower seasonality has been reported for sheep breeds from the Mediterranean countries enabling spring matings. To further substantiate this, the present study compared seasonal variation in oestrus behaviour and ovulation in two Greek breeds (Chios and Serres) maintained in the same environment. In 27 adult ewes of each breed, oestrus behaviour, the occurrence of ovulation and ovulation rate were monitored during 2 successive years by daily inspection by rams, weekly progesterone assay in circulating blood plasma and monthly ovarian laparoscopy. The periods of anoestrus (109 +/- 8 (wk) vs 178 +/- 5 d) and anovulation (63 +/- 8 vs 149 +/- 6 d) were significantly shorter (P < 0.001 and P < 0.001) and more variable in Chios than in Serres ewes. Furthermore, the percentage of ewes exhibiting oestrus at least once monthly was significantly higher from March to July in Chios than in Serres ewes. Continuous ovulation throughout the year was noted in 5 and 2 Chios ewes during year 1 and 2, respectively. Ovulation rate (3.25 +/- 0.15 vs 1.45 +/- 0.04) was higher in Chios than in Serres ewes (P < 0.001) while duration of oestrus was also longer in Chios ewes (1.8 +/- 0.05 vs 1.5 +/- 0.06 d; P = 0.002). There were significant correlations between the duration of anovulatory periods of the 2 successive years in Chios (r = 0.43) but not Serres ewes. Ovulation rate was positively related to the onset of the sexual season in Serres but not in Chios ewes. The present data suggest that: i) the efficiency of Serres but not in Chios ewes. The present data suggest that: i) the efficiency of spring mating in these breeds is suboptimal since it is a period when the percentage of ewes exhibiting oestrus and ovulation as well as ovulation rate are limited, ii) owing to the large variation in seasonality within Chios ewes and to the good between year correlation in features of seasonality, selection against seasonality in Chios ewes could be worthwhile.

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 of long and short days either attenuated (group 3) or prevented (group 2) seasonal changes in the activity of the hypothalamo-pituitary axis.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma progesterone levels during male-induced ovarian cycles were measured at three periods (March, July, November) in Creole goats. For the females experiencing a cycle of normal duration, plasma progesterone reached 2.0 ng/ml six days after male introduction. For the females experiencing a short cycle, a brief (one day) and slight (0.5 to 1.0 ng/ml) secretion of progesterone was observed during this cycle. A seasonal variation in the interval between male introduction and maximum level of progesterone during the short cycle was demonstrated (March: 4.7 days; July: 5.6 d. and November: 3.1 d.), but the maximum level reached did not vary with season (0.6; 0.9 and 0.6 ng/ml).

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.(ABSTRACT TRUNCATED AT 250 WORDS)