BACKGROUND
seasonality of reproduction is a common feature in sheep and goat breeds of temperate latitudes  <cit>  and seems to have been present for millennia in the sheep and goat breeding systems  <cit> .
the annual breeding season begins in summer in ile-de-france ewes and in autumn in alpine goats and ends in winter in both species, resulting in a marked seasonality in birth dates of lambs and kids.
in goats and sheep, this seasonality is under photoperiodic control.
in experimental conditions, long days inhibit and short days stimulate sexual activity .
however, under natural conditions of temperate countries, goats, as well as sheep  <cit> , probably have an endogenous rhythm that is synchronized by photoperiod such that breeding occurs during autumn/winter and anovulation  occurs during spring/summer.
when transferred to equatorial conditions , suffolk ewes  cycled at irregular intervals with no clear anovulatory season  <cit> .
in contrast, when transferred to tropical photoperiodic conditions where the annual amplitude of photoperiodic changes exists but is lower than in temperate regimen, alpine goats do not greatly modify the seasonal characteristics of their breeding season, and long periods of anestrus and anovulation are still present during spring and summer as in control females maintained under temperate photoperiod  <cit> .
local breeds of sheep  <cit>  and goats  <cit>  under their native tropical conditions, are either non-seasonal breeders or exhibit only a weak seasonality of reproduction.
the females of these breeds ovulate and exhibit estrus almost the whole year round, even though short periods of anovulation and anestrus are detected in some females.
two main hypotheses can be raised to explain the near-absence of seasonality: either the females are insensitive to photoperiod, or the amplitude of the photoperiodic changes is too small.
it is thus interesting to determine whether absence of seasonality persists when females of these breeds are subjected to major annual changes in the amplitude of day length, the prevailing conditions in temperate regions, or whether seasonality appears as it does in most temperate breeds.
in the present experiment, seasonal ovulatory activities were assessed in tropical creole goats and black-belly ewes.
these two breeds originate from the carribean islands, where they have been bred for 3– <dig> centuries, and constitute the progeny of african tropical breeds .
the animals of the present experiment were imported into europe and experimentally subjected for more than two years in light-proof rooms to an annual photoperiodic regimen simulating that of temperate regions , and compared to females under tropical cycle simulating that of a tropical region .
RESULTS
ovulatory activity in creole goats
ovulatory activity demonstrated marked differences between experimental groups over the course of the experiment.
individual ovulatory activity is presented in figure  <dig>
marked seasonality of ovulatory activity appeared in female goats of the te group; the seasonal inactivity occurred from may to september for the three years of the study .
the percentage of female goats experiencing at least one ovulation per month dramatically decreased from may to september for the three years .
all female goats experienced an anovulatory period during the first spring/summer season , only one of them continued its ovulatory activity in  <dig>  and all of them stopped again in may  <dig>
in contrast, female goats exposed to the tr photoperiodic cycle demonstrated much less seasonality as the percentage of goats experiencing at least one ovulation per month never went below 56% .
two female goats cycled continuously during the course of the experiment, one female goat in mid- <dig> and three in mid- <dig> continued their ovulatory activity during spring and summer, and four females were still cycling at the end of the experiment .
these differences between the two groups led to significant differences in some, but not all, parameters.
the percentage of goats experiencing at least one ovulation per month  was significantly lower in the te than in the tr group in may , june, july, august and september  <dig> , tended to be lower in may  <dig> , and was lower again in may  and june  <dig> .
in both groups the females which stopped their ovulatory activity did so at roughly the same date  in the  <dig> years of the experiment .
tr goats began their first breeding season significantly earlier than te goats in  <dig>  but this difference did not appear in the second breeding season .
variances of the dates of end of the 2nd and 3rd breeding seasons were significantly higher in tr goats .
the duration of the anovulatory period in  <dig> was significantly shorter in tr than in te goats and the duration of the 1990– <dig> breeding season was significantly longer in tr than in te goats .
the  <dig> anovulatory period and the 1991– <dig> breeding season did not differ between groups .
variances of the duration of the 2nd anovulatory season and of the 3rd breeding season were significantly higher in tr goats .
ovulatory activity in black-belly ewes
ovulatory activity demonstrated marked variations in both experimental groups over the course of the experiment.
individual ovulatory activity is presented in figure  <dig>
from october to march of the first year, all females were cycling in both groups .
in the tr group, ovulatory activity dropped in april, remained low  in may and june, then rose again in july and august to reach its maximum from september to april of the next year; minimum activity was observed again from may to august, before a maximal activity in september and october.
ewes of the te group roughly followed the same pattern, with a later onset of cyclicity in september of the first year ; and a later end in may-june of the second year .
the percentage of cycling females never went below 17% .
one ewe in the te group never stopped cycling during the course of the experiment.
mean dates of the end of the breeding season did not differ between tr and te ewe groups in the first and second year .
the onset of the breeding season occurred earlier in tr than in te for the first year, but not for the second year .
thus, duration of the first and second anestrous seasons and/or duration of the sexual season did not differ between tr and te ewe groups .
variances of the durations of anovulatory and of breeding seasons were significantly higher in te ewes .
discussion
the two tropical breeds of creole goats and black-belly ewes used in the present study demonstrated clear seasonal breeding activity with a definite cut-off when maintained under the simulated extensive photoperiodic variations of temperate areas.
as many other goat and sheep breeds originating and raised under a temperate climate, these two breeds imported from the tropics displayed cessation of ovulatory activity in spring and summer, i.e.
the usual months for anovulation and anestrus in a temperate climate.
even though it appears that their anovulatory season seemed shorter than european breeds of goats  and sheep , almost all black-belly ewes stopped their ovulatory activity for about  <dig> months and creole goats for  <dig>  months.
black-belly ewes stopped their ovulatory activity late in the year  as compared to the majority of breeds, for example ile-de-france breed .
however, this was not true for the onset of the breeding season which generally started in september-october in both goat breeds.
the control group of goats maintained under simulated tropical photoperiodic variations displayed significantly less seasonality.
the percentage of goats showing at least one ovulation per month was significantly higher in may and june for  <dig> years out of  <dig>  and did not drop to  <dig> as it did in the temperate group of goats.
a relatively high number of female goats did not experience an anovulatory season either at all or during some years of the experiment, and those that did showed a significantly shorter anovulatory period during the first year of the experiment.
thus, the comparison between creole female goats maintained under simulated temperate photoperiod and control females placed under simulated tropical photoperiod leads to the conclusion that their breeding season is sensitive to large photoperiodic variations.
in contrast, black-belly ewes maintained under simulated tropical photoperiodic variations did not differ greatly from those maintained under simulated temperate photoperiod.
the two groups of ewes and goats used here differed in various parameters, some of which could explain the photoperiod x species interaction observed here:  recipient ewes in which embryos were implanted in autumn were maintained under natural photoperiod.
it is known that light changes during pregnancy may affect the progeny's photoperiod sensitivity, especially regarding the onset of puberty in sheep  <cit>  and in rodents  <cit> .
this was not the case in the goats, as these experimental animals were the 3nd or 4th progeny of females imported as embryos.
experimental ewes were artificially raised in te vs tr photoperiod from birth to  <dig> months old from the start of the experiment, whereas female goats were raised under simulated tropical photoperiod until the start of the experiment at one or two years old.
black-belly ewes were included in the experiment at  <dig> months of age, whereas creole goats were  <dig> and  <dig> months old at the start of the experiment.
these three main differences between the experiments in female goats and ewes could possibly explain this photoperiod x species interaction.
however, it may also come from a real difference of sensitivity to non-photoperiodic factors  between the two species.
the spontaneous ovulatory activity demonstrated in the present experiment by the black-belly ewes from the tr group were very different from those registered earlier in their natural breeding conditions on the island of martinique in the tropics, where they cycled all year round  <cit> .
the creole goats from the simulated tropical photoperiod did not display here the same results as females of the same flock raised in their natural breeding conditions on the island of guadeloupe in the tropics, where they also cycled almost continuously  <cit> .
this unexpected difference suggests that other external cues may act in combination with photoperiod to inhibit breeding activity.
the fact that all animals simultaneously stopped cycling in spring, suggests that an external physical cue could be involved.
the temperature of the light-proof rooms in which the experiments were performed was not controlled and the high and low-amplitude variations of air temperature of the tropics were not applied to our experimental animals.
such a cue may interact with photoperiod and enhance the negative effects of the limited photoperiodic changes, which do not appear in normal tropical conditions.
to our knowledge, very few experiments have been carried out in sheep and/or goats to determine the role played by low temperature in the appearance of seasonality.
it has been demonstrated that inversion of the temperature rhythm does not entrain ovulatory activity in ewes of a european breed maintained under an equatorial photoperiodic schedule  <cit>  and that low temperatures in the summer time may induce an 8-week advance in the onset of the annual breeding season in dark-faced ewes  <cit> .
in suffolk ewes, a seasonal breed, the maintenance of ewes under an equatorial regimen with a limited but efficient control of temperature change amplitude, induced cycles at irregular intervals with no clear anovulatory season  <cit>  however, in other species it has been clearly demonstrated that the combination of photoperiod and temperature is responsible for seasonal changes in reproductive activity  <cit> .
thus, it is possible that, in the absence of a major cue , seasonal ovulatory activity of females of the tr groups has been entrained by temperature.
in syrian hamsters, exercise by access to a running wheel can completely inhibit the short-day induced regression of the testis  <cit> .
experimental creole goats and black belly ewes of the present experiment were raised in light-proof rooms where physical exercise was limited, whereas in their original management conditions where the initial observations were done  <cit> , animals were maintained at pasture.
thus, it is possible that in their original management conditions, physical exercise prevented the inhibitory effects of the  <dig> hours of light that was observed in our experimental light-proof rooms in the tr groups of goats and ewes.
the sheep and goat breeds used here are local breeds of the carribean islands.
even though their presence in these islands is associated with human history, they are considered as the progeny of tropical but not european ancestors, because they originate from the west coast of tropical africa .
in these areas all sheep and goat breeds are considered as non or low seasonal breeders.
thus, the sensitivity of the creole goats and black-belly ewes observed here under temperate photoperiod could be hypothetized as a true sensitivity of these breeds, not a simple inheritance of a trait coming from european ancestors.
CONCLUSIONS
a marked seasonality in the ovulatory activity of tropical creole goats and black-belly ewes was induced when females were exposed to a simulated temperate photoperiod.
unexpectedly, and differing from the results obtained in their original breeding location, black-belly ewes and, to a lesser extent, creole goats exposed to a simulated tropical photoperiod also showed significant seasonality in their ovulatory activity.
such results indicate that both species are capable of showing seasonality under the the photoperiodic changes of the temperate zone even though they do not originate from these regions.

 seasonality of reproduction is a common feature in sheep and goat breeds of temperate latitudes and seems to have been present for millennia in the sheep and goat breeding systems. the annual breeding season begins in summer in ile-de-france ewes and in autumn in alpine goats and ends in winter in both species, resulting in a marked seasonality in birth dates of lambs and kids. in goats and sheep, this seasonality is under photoperiodic control. in experimental conditions, long days inhibit and short days stimulate sexual activity. however, under natural conditions of temperate countries, goats, as well as sheep, probably have an endogenous rhythm that is synchronized by photoperiod such that breeding occurs during autumn/winter and anovulation occurs during spring/summer. when transferred to equatorial conditions, suffolk ewes cycled at irregular intervals with no clear anovulatory season. in contrast, when transferred to tropical photoperiodic conditions where the annual amplitude of photoperiodic changes exists but is lower than in temperate regimen, alpine goats do not greatly modify the seasonal characteristics of their breeding season, and long periods of anestrus and anovulation are still present during spring and summer as in control females maintained under temperate photoperiod. local breeds of sheep and goats under their native tropical conditions, are either non-seasonal breeders or exhibit only a weak seasonality of reproduction. the females of these breeds ovulate and exhibit estrus almost the whole year round, even though short periods of anovulation and anestrus are detected in some females. two main hypotheses can be raised to explain the near-absence of seasonality: either the females are insensitive to photoperiod, or the amplitude of the photoperiodic changes is too small. it is thus interesting to determine whether absence of seasonality persists when females of these breeds are subjected to major annual changes in the amplitude of day length, the prevailing conditions in temperate regions, or whether seasonality appears as it does in most temperate breeds. in the present experiment, seasonal ovulatory activities were assessed in tropical creole goats and black-belly ewes. these two breeds originate from the carribean islands, where they have been bred for 3– centuries, and constitute the progeny of african tropical breeds. the animals of the present experiment were imported into europe and experimentally subjected for more than two years in light-proof rooms to an annual photoperiodic regimen simulating that of temperate regions, and compared to females under tropical cycle simulating that of a tropical region.  ovulatory activity in creole goats ovulatory activity demonstrated marked differences between experimental groups over the course of the experiment. individual ovulatory activity is presented in figure marked seasonality of ovulatory activity appeared in female goats of the te group; the seasonal inactivity occurred from may to september for the three years of the study. the percentage of female goats experiencing at least one ovulation per month dramatically decreased from may to september for the three years. all female goats experienced an anovulatory period during the first spring/summer season, only one of them continued its ovulatory activity in and all of them stopped again in may in contrast, female goats exposed to the tr photoperiodic cycle demonstrated much less seasonality as the percentage of goats experiencing at least one ovulation per month never went below 56%. two female goats cycled continuously during the course of the experiment, one female goat in mid- and three in mid- continued their ovulatory activity during spring and summer, and four females were still cycling at the end of the experiment. these differences between the two groups led to significant differences in some, but not all, parameters. the percentage of goats experiencing at least one ovulation per month was significantly lower in the te than in the tr group in may, june, july, august and september, tended to be lower in may, and was lower again in may and june. in both groups the females which stopped their ovulatory activity did so at roughly the same date in the years of the experiment. tr goats began their first breeding season significantly earlier than te goats in but this difference did not appear in the second breeding season. variances of the dates of end of the 2nd and 3rd breeding seasons were significantly higher in tr goats. the duration of the anovulatory period in was significantly shorter in tr than in te goats and the duration of the 1990– breeding season was significantly longer in tr than in te goats. the anovulatory period and the 1991– breeding season did not differ between groups. variances of the duration of the 2nd anovulatory season and of the 3rd breeding season were significantly higher in tr goats. ovulatory activity in black-belly ewes ovulatory activity demonstrated marked variations in both experimental groups over the course of the experiment. individual ovulatory activity is presented in figure from october to march of the first year, all females were cycling in both groups. in the tr group, ovulatory activity dropped in april, remained low in may and june, then rose again in july and august to reach its maximum from september to april of the next year; minimum activity was observed again from may to august, before a maximal activity in september and october. ewes of the te group roughly followed the same pattern, with a later onset of cyclicity in september of the first year; and a later end in may-june of the second year. the percentage of cycling females never went below 17%. one ewe in the te group never stopped cycling during the course of the experiment. mean dates of the end of the breeding season did not differ between tr and te ewe groups in the first and second year. the onset of the breeding season occurred earlier in tr than in te for the first year, but not for the second year. thus, duration of the first and second anestrous seasons and/or duration of the sexual season did not differ between tr and te ewe groups. variances of the durations of anovulatory and of breeding seasons were significantly higher in te ewes. discussion the two tropical breeds of creole goats and black-belly ewes used in the present study demonstrated clear seasonal breeding activity with a definite cut-off when maintained under the simulated extensive photoperiodic variations of temperate areas. as many other goat and sheep breeds originating and raised under a temperate climate, these two breeds imported from the tropics displayed cessation of ovulatory activity in spring and summer, i.e. the usual months for anovulation and anestrus in a temperate climate. even though it appears that their anovulatory season seemed shorter than european breeds of goats and sheep, almost all black-belly ewes stopped their ovulatory activity for about months and creole goats for months. black-belly ewes stopped their ovulatory activity late in the year as compared to the majority of breeds, for example ile-de-france breed. however, this was not true for the onset of the breeding season which generally started in september-october in both goat breeds. the control group of goats maintained under simulated tropical photoperiodic variations displayed significantly less seasonality. the percentage of goats showing at least one ovulation per month was significantly higher in may and june for years out of and did not drop to as it did in the temperate group of goats. a relatively high number of female goats did not experience an anovulatory season either at all or during some years of the experiment, and those that did showed a significantly shorter anovulatory period during the first year of the experiment. thus, the comparison between creole female goats maintained under simulated temperate photoperiod and control females placed under simulated tropical photoperiod leads to the conclusion that their breeding season is sensitive to large photoperiodic variations. in contrast, black-belly ewes maintained under simulated tropical photoperiodic variations did not differ greatly from those maintained under simulated temperate photoperiod. the two groups of ewes and goats used here differed in various parameters, some of which could explain the photoperiod x species interaction observed here: recipient ewes in which embryos were implanted in autumn were maintained under natural photoperiod. it is known that light changes during pregnancy may affect the progeny's photoperiod sensitivity, especially regarding the onset of puberty in sheep and in rodents. this was not the case in the goats, as these experimental animals were the 3nd or 4th progeny of females imported as embryos. experimental ewes were artificially raised in te vs tr photoperiod from birth to months old from the start of the experiment, whereas female goats were raised under simulated tropical photoperiod until the start of the experiment at one or two years old. black-belly ewes were included in the experiment at months of age, whereas creole goats were and months old at the start of the experiment. these three main differences between the experiments in female goats and ewes could possibly explain this photoperiod x species interaction. however, it may also come from a real difference of sensitivity to non-photoperiodic factors between the two species. the spontaneous ovulatory activity demonstrated in the present experiment by the black-belly ewes from the tr group were very different from those registered earlier in their natural breeding conditions on the island of martinique in the tropics, where they cycled all year round. the creole goats from the simulated tropical photoperiod did not display here the same results as females of the same flock raised in their natural breeding conditions on the island of guadeloupe in the tropics, where they also cycled almost continuously. this unexpected difference suggests that other external cues may act in combination with photoperiod to inhibit breeding activity. the fact that all animals simultaneously stopped cycling in spring, suggests that an external physical cue could be involved. the temperature of the light-proof rooms in which the experiments were performed was not controlled and the high and low-amplitude variations of air temperature of the tropics were not applied to our experimental animals. such a cue may interact with photoperiod and enhance the negative effects of the limited photoperiodic changes, which do not appear in normal tropical conditions. to our knowledge, very few experiments have been carried out in sheep and/or goats to determine the role played by low temperature in the appearance of seasonality. it has been demonstrated that inversion of the temperature rhythm does not entrain ovulatory activity in ewes of a european breed maintained under an equatorial photoperiodic schedule and that low temperatures in the summer time may induce an 8-week advance in the onset of the annual breeding season in dark-faced ewes. in suffolk ewes, a seasonal breed, the maintenance of ewes under an equatorial regimen with a limited but efficient control of temperature change amplitude, induced cycles at irregular intervals with no clear anovulatory season however, in other species it has been clearly demonstrated that the combination of photoperiod and temperature is responsible for seasonal changes in reproductive activity. thus, it is possible that, in the absence of a major cue, seasonal ovulatory activity of females of the tr groups has been entrained by temperature. in syrian hamsters, exercise by access to a running wheel can completely inhibit the short-day induced regression of the testis. experimental creole goats and black belly ewes of the present experiment were raised in light-proof rooms where physical exercise was limited, whereas in their original management conditions where the initial observations were done, animals were maintained at pasture. thus, it is possible that in their original management conditions, physical exercise prevented the inhibitory effects of the hours of light that was observed in our experimental light-proof rooms in the tr groups of goats and ewes. the sheep and goat breeds used here are local breeds of the carribean islands. even though their presence in these islands is associated with human history, they are considered as the progeny of tropical but not european ancestors, because they originate from the west coast of tropical africa. in these areas all sheep and goat breeds are considered as non or low seasonal breeders. thus, the sensitivity of the creole goats and black-belly ewes observed here under temperate photoperiod could be hypothetized as a true sensitivity of these breeds, not a simple inheritance of a trait coming from european ancestors.  a marked seasonality in the ovulatory activity of tropical creole goats and black-belly ewes was induced when females were exposed to a simulated temperate photoperiod. unexpectedly, and differing from the results obtained in their original breeding location, black-belly ewes and, to a lesser extent, creole goats exposed to a simulated tropical photoperiod also showed significant seasonality in their ovulatory activity. such results indicate that both species are capable of showing seasonality under the the photoperiodic changes of the temperate zone even though they do not originate from these regions. 
this study was therefore designed to determine whether tropical creole goats and black-belly ewes are sensitive to temperate photoperiod. 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. 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. tropical female goats demonstrated much less seasonality, as the percentage of goats experiencing at least one ovulation per month never went below 56%. 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. seasonality of ovulatory activity is observed in european sheep and goat breeds, whereas tropical breeds show almost continuous ovulatory activity. ovulatory activity was determined by blood progesterone assays for more than two years. 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. it is not known if these tropical breeds are sensitive or not 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 or tropical photoperiods.
 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 or tropical photoperiods. ovulatory activity was determined by blood progesterone assays for more than two years. the experiment lasted months in goats and months in ewes.  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. 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 or september. the percentage of ewes experiencing at least one ovulation per month never went below 8% and 17% during the spring and summer months.  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. 