Abolition of seasonal variations in semen quality and maintenance of sperm fertilizing ability by photoperiodic cycles in goat bucks

SmallRuminant Research, 9 (1992) 47-59

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© 1992 Elsevier Science Publishers B.V. All rights reserved. 0921-4488/92/$05.00

Abolition of seasonal variations in semen quality and maintenance of sperm fertilizing ability by photoperiodic cycles in goat bucks J.A. Delgadillo ~, B. Leboeuf and P.Chemineau LN.R.A. Reproductive Physiology, Nouzilly, France (Accepted 16 October 1991 )

ABSTRACT Delgadillo, J.A., Leboeuf, B. and Chemineau, P., 1992. Abolition of seasonal variations in semen quality and maintenance of sperm fertilizing ability by photoperiodic cycles in bucks. Small R umin. Res., 9: 47-59. Goat bucks show large seasonal variations in semen quality mainly influenced by photoperiodic changes. Minimum percentage of motile sperm cells and velocity occur during spring and summer. Three groups of Alpine and Saanen bucks (n = 6 in each group ) were used to determine whether rapid alternations between long and short days were able to abolish seasonal variations in semen quality. One group remained in open sheds under natural day length (An) which varied from 16 h light (June) to 8 h light per day (December). The first experimental group (2Mo) was exposed to alternations between 1 month of long days (16L:8D) and 1 month of short days (8L:16D) and the second one (4Mo) to alternations between 2 months of long days ( 16L:8D ) and 2 months of short days ( 8L: 16D ), during two consecutive years. All parameters of semen quality before freezing and after thawing varied with time in the three groups (P< 0.05 ). Interaction between group and time was also detected for five parameters out of six (P< 0.001 ), indicating that groups varied differently with time. Semen quality in the experimental groups was not affected by prevailing day length. As expected, in group An, the percentage of motile sperm and sperm motility score (0-5) before freezing and after thawing decreased during the nonbreeding season (March to August; minimum in August: 37.8% and 2.4 score before freezing) compared to the breeding season (September to February; maximum in January: 66.3% and 3.6 score before freezing). The production of semen doses available for A.I. also decreased during this period. In contrast, in the two experimental groups the decrease in sperm quality during this period was prevented. In these groups, the percentage of motile sperm and sperm motility before freezing and after thawing remained at the same level as observed in group An during the natural breeding season. Abolition of seasonal variation in semen quality led to production of 69.0 and 54.7% more A.I. doses in groups 2Mo and 4Mo than in group An. Sperm fertility in the three groups did not show significant differences (59.4% of kiddings in 1599 goats from 58 flocks). It was concluded that, in goat bucks, alternations between long and short days abolished the seasonal variation in semen quality without altering sperm fertility.

Correspondence to: P. Chemineau, I.N.R.A. Reproductive Physiology, 37380 Nouzilly, France. JPresent address: Universidad Aut6noma Agraria Antonio Narro, Carretera a Sta. F6 y Perif6rico. Apdo postal 940, Torre6n, Coahuila, M6xico.

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J.A. DELGADILLO ET AL.

INTRODUCTION

In rams and goat bucks, spermatogenic activity shows large seasonal variations (Pelletier et al., 1988 ). In these species, a decrease in quantitative and qualitative semen production and sperm fertility during the non-breeding season (March to August) has been reported (goats: Corteel, 1975, 1977; sheep: Colas, 1980). Variations in spermatogenic activity are mainly influenced by photoperiodic changes, i.e., increasing day length reduces the spermatogenic activity (Ortavant, 1959 ). It was recently shown that in goat bucks alternations between long and short days abolished the seasonal variations in quantitative semen production (DelgadiUo et al., 1991 ). The aim of this study was to determine whether alternations between long and short days were able to abolish the dramatic seasonal variations in semen quality and to maintain a high sperm fertility in goat bucks. MATERIALSAND METHODS Animals The experiment was carried out between 1 January 1987 and 31 December 1988 using Alpine and Saanen goat bucks at the Artificial Insemination Research Station of Rouillr, France (46 °N Latitude). The animals were 346 ___7 days old (mean___S.E. ) at the beginning of the experiment. On 20 December 1986, they were allocated to three groups of six animals according to their breed (so that the number of animals in each breed was balanced in each treatment group), their body and testicular weight, and their semen production during their first sexual season (from September to December 1986). Animals were fed daily a diet of 1.0 kg hay, 0.6 kg barley straw, 0.6 kg oats and 0.4 kg commercial concentrates. Level of feeding was + 3% for energy and + 43% for protein requirements at INRA standards. They had free access to water and to mineral blocks containing oligoelements and vitamins. Photoperiodic treatments The first group of males (annual day length: An) remained in open sheds in individual pens (2.5 × 1.1 m) under natural day length and ambient temperature. The photoperiod varied from 16 h of light at the summer solstice to 8 h of light at the winter solstice. The second group (2Mo) was housed in a light-proof building and exposed to alternations between 1 month of long days (16L:8D) and 1 month of short days (8L: 16D). The third group (4Mo) was also housed in a light-proof building and exposed to alternations between 2 months of long days (16L:8D) and 2 months of short days (8L:16D). All experimental goat bucks from these two groups were placed in individual pens ( 1.8 × 1.7 m ). The photoperiod was regulated by electric clocks that operated bulbs providing an intensity of 300 lux lateral to goat eyes. Lights were turned

SEMEN QUALITY AND MAINTENANCE OF SPERM FERTILIZING ABILITY BY PHOTOPERIODIC CYCLES

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on at 07:00 h and turned offat 23:00 h (in long days) or 15:00 h (in short days). The mean minimal temperature in open sheds was registered in December ( + 5°C) and the mean maximal temperature in July ( + 3 2 ° C ) ; in light-proof buildings the corresponding temperatures were + 5 and + 30 ° C, respectively.

Semen collection and sperm quality Semen was collected twice a week during two consecutive years and sperm cells were deep-frozen once a week according to the technique of Corteel (1974). Semen quality was estimated by assessing the percentage of motile sperm and sperm progressive motility (scale 0-5) at three different times: before freezing ( + 4 °C), 5 and 120 min after thawing. The straws selected for artificial insemination were those which exhibited at least 30% of live spermatozoa and 3.0 score of progressive motility 5 min after thawing. Sperm morphology was assessed once or twice a month between November 1987 and October 1988. After sperm collection, 0.05 ml of semen was diluted into 0.05 ml of buffer solution (used for washing semen; Corteel, 1974), then, one drop of diluted semen was mixed with an eosine-nigrosine solution and sperm abnormalities were determined by direct count of 150 cells as described by Colas (1980).

Fertilizing ability To compare the fertilizing ability of semen produced by goat bucks from the three groups, 1599 goats of 58 private flocks were inseminated from May to August during two consecutive years ( 1987 and 1988 ). Sperm used for A.I. was produced in October-November (period of natural breeding season) and April-May (period of natural non-breeding season ). Alpine and Saanen does were synchronised and inseminated after hormonal treatment as described by Corteel et al. ( 1988 ). In each flock, semen produced in both periods by each group was used and does were divided into equal groups according to their milk production, age and interval between parturition and A.I. Fertility was expressed as percentage of does kidding.

Data analysis Analysis of variance (ANOVA) of the percentage of motile sperm and sperm progressive motility was performed using a monthly mean for each male and testing the effects of group, month, year and interactions (Dagnrlie, 1969); thereafter, the monthly means were compared by Student's t-test (Snedecor and Cochran, 1980). Production of A.I. doses was analysed by ANOVA using monthly production by each male and testing the effects of bucks and time. In the experimental groups, monthly (2Mo) and bi-monthly means (4Mo) were calculated and analysed by ANOVA to compare the results obtained during long and short days (prevailing day length).

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Production of doses by each group was compared by the Mann-Whitney non-parametric test (Dagn61ie, 1969). Percentage of kidding females was compared by chi-square test (Dagn61ie, 1969). RESULTS

All parameters of semen quality before freezing and after thawing in the three groups varied with month ( P < 0.0001 ) but not with groups. Interaction between group and month was also detected for five parameters out of six ( P < 0.05) indicating that the groups varied differently with time. Effects of year and of interaction year-group were not significant for any of the studied parameters. Semen quality in the experimental groups was not affected by prevailing day length. 90 2Mo (*) vs An (0) 70

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Months Fig. 1. Percentage of motile sperm after cooling the semen of Alpine and Saanen bucks of 3 groups subjected to photoperiodic changes. Monthly mean + S.E. The grey areas show the significant differences between groups ( B, P < 0.05; m, P < 0.01 ). An: natural photoperiodic variations at 46°N latitude. 2Mo: alternation between 1 month of long days (16L:8D) and 1 month of short days ( 8L: 16D). 4Mo: alternation between 2 months of long days (16L:gD) and 2 months of short days (gL: 16D).

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2Mo (*) vs An (u) 4.0 =

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Months Fig. 2. Sperm progressive motility (scale 0 to 5 ) after cooling the semen of Alpine and Saanen bucks of three groups subjected to photoperiodic changes. Monthly mean + S.E. The grey areas show the significant differences between groups. See legend Fig. 1 for explanation.

Sperm quality beforefreezing Seasonal variations in sperm quality in group An were prevented in both treated groups. In 2 experimental years, the semen quality of group An was low during the non-breeding season (March to August ) and high during the breeding season (September to February). The lowest percentage of motile sperm (Fig. 1) occurred in August of the first year (37.8%+9.6) and the highest in January of the second experimental year (66.2%_+2.6). In contrast, only slight variations of this parameter were observed in treated groups. In group 2Mo, the values registered in August and January were 55.3 _+3.9 and 69.5% _+4.6, respectively, whereas in group 4Mo, these percentages were 55.4 _+4.6 and 67.4% ___ 3.2, respectively. Sperm progressive motility also showed dramatic seasonal variations in group An, which were abolished in the treated groups (Fig. 2 ). In group An, a progressive decrease in sperm motility occurred at the beginning of the study and the lowest score of 2.4 + 0.5 was recorded in August. Motility then increased progressively and maximal values were registered in January of the second experimental year ( 3.6 _+0.1 ). This was followed by a decrease similar

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J.A. D E L G A D I L L O ET AL.

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Months Fig. 3. Percentage of motile sperm 5 min after thawing the semen of Alpine and Saanen bucks of three groups subjected to photoperiodic changes. Monthly mean + S.E. The grey areas show the significant differences between groups ( P < 0.05). For explanation see legend Fig. 1.

to that observed during the first year. Opposite to that, an elevated sperm motility was maintained in the two experimental groups throughout the study. Although a decline in sperm motility was recorded in treated animals during the last 2 months of the study, the values obtained in group 2Mo were similar in August (3.3 + 0 . 2 ) and in January ( 3 . 7 _ 0 . 1 ) . The values of group 4Mo corresponding to these months were 3.4 + 0.1 and 3.7 ___0.1, respectively.

Sperm quality 5 and 120 min after thawing Seasonal variations in sperm quality before freezing in group An persisted 5 min after thawing. In the first year, the percentage of motile sperm, 5 min after thawing (Fig. 3), did not show any difference between groups, but in group An this percentage varied during the second year from 24.9% ___3.8 in May to 51.7% _+4.3 in December. In contrast, these variations were abolished in the experimental groups. In group 2Mo, the percentage of motile sperm remained at a more steady level than in group 4Mo. In fact, in group 2Mo, these percentages were similar in May (41.8%+4.9) and in December

SEMEN QUALITY AND MAINTENANCE OF SPERM FERTILIZING ABILITY BY PHOTOPERIODIC CYCLES

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Months Fig. 4. Sperm progressive motility (scale 0 to 5) 5 min after thawing the semen of Alpine and Saanen bucks of three groups subjected to photoperiodic changes. Monthly mean_+ S.E. The grey areas show the significant differences between groups ( P < 0.05). For explanation see legend Fig. 1.

(41.0% _+8.9 ). Nevertheless, in group 4Mo, slight variations linked with photoperiodic changes were observed and the values registered were 38.8% + 5.3 in May and 40.1% + 8.2 in December. In the untreated group An, the sperm progressive motility also showed large seasonal variations (Fig. 4). Elevated sperm mobility was observed during the natural breeding season which declined during the non-breeding season. In the second year, motility varied from 2.1 ___0.5 in August to 3.1 + 0.2 in December. In the treated groups, the sperm motility was high throughout the study. However, this motility decreased during the last 3 (group 2Mo) and 2 (group 4Mo) months. Thus, in group 2Mo, the sperm motility was 2.8 ___0.2 in August and 2.4 ___0.5 in December, whereas in group 4Mo, in which sperm motility demonstrated slight variations according to photoperiodic changes, this parameter was very similar in August (2.5_+0.1) and in December (2.8_+0.2).

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J.A. DELGADILLO ET AL.

20 ,

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Months Fig. 5. Percentage of abnormal spermatozoa in the semen of Alpine and Saanen bucks of 3 groups subjectedto photoperiodic changesduring one singleyear of the experiment (November 1987-October 1988). Monthly mean. For explanation see legend Fig. 1. The same trends of semen quality observed in treated and control animals 5 min after thawing, were also recorded 120 min after thawing.

Spermatozoa abnormalities In the three groups, sperm abnormalities varied with m o n t h ( P < 0 . 0 5 ) . Interaction between group and m o n t h was detected ( P < 0.01 ). In the experimental animals, sperm morphology was not affected by the prevailing day length. In group An, a significant rise in the percentage of abnormal spermatozoa only occurred in July ( P < 0.05). In groups 2Mo and 4Mo, no significant rise in this parameter was observed and the abnormal sperm cells remained lower than 15% (Fig. 5 ). Mean percentages of abnormal sperm cells ( _ S . E . ) were 10.3 (-+0.9), 5.6 (_+0.8) and 6.4% (_+0.8) for groups An, 2Mo and 4Mo, respectively.

Production of A.L doses In the three groups, production of A.I. doses varied with m o n t h ( P < 0.05 ). Individual difference in production was also found ( P < 0.05 ). During the non-breeding seasons of the experimental period (i.e., from March to August), bucks from group 2Mo and 4Mo produced 84.2 and 108.1% more A.I. doses, respectively, than group An. This superiority was even observed during the natural breeding seasons: 66.4 and 15.9%, respectively. However, the coefficients of variation in the n u m b e r of doses produced were higher in 2Mo (73.1%) than in 4Mo (37.5%) and in group An (42.8%). N u m b e r of A.I.

SEMEN QUALITY AND MAINTENANCE OF SPERM FERTILIZING ABILITY BY PHOTOPERIODIC CYCLES 5 5

doses (mean+_S.E. ) produced by the three groups was 505 +_88 (group An, range 246-882), 854+_255 (group 2Mo, range 348-1909) and 782_+ 120 (group 4Mo, range 412-1229 ). The 4Mo group produced significantly more total A.I. doses than the An group ( P < 0.05 ), while production of the 2Mo group was not different from the two other groups.

Sperrn fertility Fertility of the semen produced during breeding and non-breeding season in the three groups and used for A.I. did not show any significant difference. The percentage of kidding females was 62.5% (group An), 57.9 (group 2Mo ) and 57.8 (group 4Mo). In each group, no significant difference of sperm fertility was found among bucks. Sperm fertility was not influenced by the inseminators or months in which A.I. was performed. In contrast, there was a flock effect on sperm fertility ( P < 0.05; range 30-87%). DISCUSSION The present findings demonstrate that short photoperiodic cycles applied to goat bucks abolished the seasonal variations of semen quality observed in control animals. This allowed both treated groups to produce more A.I. doses than the control group. The seasonal variations recorded in group An were consistent with results reported earlier by Corteel ( 1977 ). In the experimental groups, semen quality before freezing remained at the level recorded in group An during the natural sexual season. These findings agree with Chemineau et al. (1988) for light-treated Ile-de-France rams in which semen quality remained at the same level as in control animals during the natural breeding season. Live spermatozoa 5 and 120 min after thawing were very similar in groups An, 2Mo and 4Mo during the first experimental year. The relatively low percentage of motile sperm during the first year could be partly explained by the time lag for the response of animals to treatments at the beginning of the study when low testis weight was registered (Delgadillo et al., 1991 ), indicating a low spermatogenic activity (Courot, 1962; Lino, 1972). Although the annual seasonal variations were prevented in goat bucks of group 4Mo, they showed slight variations, linked to the photoperiodic regimen because periods of short days induced an enhancement of testicular gain and, hence, a higher spermatogenic activity. The periods of testicular stimulation alternated with periods of quiescence induced by long days. Testicular weight variations were less pronounced in group 2Mo, due to photoperiod changes, and the spermatogenic activity remained at a more stable level (Delgadillo et al., 1991). Endocrine parameters measured in the same animals suggest that moderate LH and testosterone release in light treated goat bucks (Delgadillo and

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Chemineau, 1991 ) may give rise to good epididymal function and sperm motility (Fournier-Delpech et al., 1979; Dacheux et al., 1987 ). In group An, the low LH and testosterone levels during the non-breeding season (Delgadillo and Chemineau, 1991 ) might, at least in part, explain the decrease in sperm progressive motility during this period. In keeping with the abolition of sexual behaviour and quantitative sperm production described by Delgadillo et al. ( 1991 ), our findings showed that semen of males subjected to alternation of long and short days can be collected and used satisfactorily all year round. Photoperiodic treatments in this study did not alter semen fertility as percentage of females kidding after A.I. did not show any significant betweengroup difference. Fertility of semen produced by group An during the breeding and non-breeding season was not different. This finding was not consistent with that reported earlier by Corteel et al. (1980), who showed that the fertility of semen collected during the breeding season was higher than that of semen collected during the non-breeding season. This discrepancy might be explained by the fact that the ejaculates were most likely subjected to a stronger selection in our study. This may have led to a reduction of the differences in sperm fertility in the An group. In conclusion, a high semen quality can be maintained by alternations of long and short days. Moreover, these photoperiodic treatments allowed to increase the production of A.I. doses without altering sperm fertility. ACKNOWLEDGMENTS

The authors wish to thank Y. Berson, D. Bernelas, A. Boisseau, J.L. Bonn6 and J. Boutain for their technical assistance and Miss Kirsten Rerat for help in the English version of this manuscript. This experiment was supported by R6gion Poitou-Charentes; while in France, J.A.D. was supported by CONACYT-CEFI.

REFERENCES Chemineau, P., Pelletier, J., Gu6rin, Y., Colas, G., Ravault, J.P., Tour6, G., Almeida, G., Thimonier, J. and Ortavant, R., 1988. Photoperiodic and melatonin treatments for the control of seasonal reproduction in sheep and goats. Reprod. Nutr. D6velop., 28: 409-422. Colas, G., 1980. Variations saisonni~res de la qualit6 du sperme chez le b61ier Ile-de-France. I. Etude de la morphologie cellulaire et de la motilit6 massale (Seasonal variations in semen quality in the Ile-de-France ram. I study of sperm morphology and of wave motion). Reprod. Nutr. D6velop., 20:1789-1799. Corteel, J.M., 1974. Viabilit6 des spermatozo'ides de bouc conserv6s et congel6s avec ou sans leur plasma s6minal: effet du glucose (Viability of goat buck sperm stored and deep-frozen with and without their seminal plasma: effects of glucosis). Ann. Biol. Anim. Bioch. Biophys., 14: 741-745.

SEMENQUALITYAND MAINTENANCEOF SPERMFERTILIZINGABILITYBYPHOTOPERIODICCYCLES 57 Corteel, J.M., 1975. Production du sperme chez le bouc: variations saisonni6res de la quantit6 et de la qualit6 du sperme r6colt6 selon l'fige des animaux (Sperm production in the goat buck: seasonal variations in the quantity and quality of sperm related to age of animals). 16res Journ6es Rech. Ovine et Caprine, INRA-ITOVIC (Editors)., Paris, II, pp. 4-17. Corteel, J.M., 1977. Production, storage and insemination of goat semen. In: Management of Reproduction in Sheep and Goats, Symposium, University of Wisconsin (Editor), Madison, July 24-25, pp. 41-57. Corteel, J.M., Baril, G. and Leboeuf, B., 1980. Residual seasonal variations in fertility in selected deep-frozen ejaculates of European dairy male goats. In Proc. 9th Inter. Congr. Anim. Reprod. Artif. Insem., Madrid, V, pp. 422-425. Corteel, J.M., Leboeuf, B. and Baril, G., 1988. Artificial breeding of adult goats an kids induced with hormones to ovulate outside the breeding season. Small Rumin. Res., 1:19-35. Courot, M., 1962. D6veloppement du testicule chez ragneau. Etablissement de la spermatog6n6se (Testis growth in the ram lamb. Establishment of spermatogenesis). Ann. Biol. Anim. Bioch. Biophys., 2: 25-41. Dacheux, J.L., Chevrier, C. and Lanson, Y., 1987. Motility and surface transformations of human spermatozoa during epididymal transit. Cell. Biol. Test. Epididymis, 513: 560-563. Dagn61ie, P., 1969. Th6orie et m6thodes statistiques I + II (Statistical Theory and Methods). Presses Agronomiques de Gembloux, Belgique. DelgadiUo, J.A., Leboeuf, B. and Chemineau, P., 1991. Decrease in the seasonality of sexual behavior and sperm production in bucks by exposure to short photoperiodic cycles. Theriogenology, 36: 755-770. Delgadillo, J.A. and Chemineau, P., 1991. Abolition of the seasonal release of LH and testosterone in Alpine male goats (Capra hircus) by short photoperiodic cycles. J. Reprod. Fert., 94: 45-55. Fournier-Delpech, S., Colas, G., Courot, M., Ortavant, R. and Brice, G., 1979. Epididymal sperm maturation in the ram. Motility, fertilizing ability and embryonic survival after uterine artificial insemination in the ewe. Ann. Biol. Anim. Bioch. Biophys., 19: 597-605. Lino, B.F., 1972. The output of spermatozoa in rams. II. Relationship to scrotal circumference, testis weight, and the number of spermatozoa in different parts of the urogenital tract. Aust. J. Biol. Sci., 25: 359-366. Ortavant, R., 1959. D6roulement et dur6e du cycle spermatog6n6tique chez le b61ier (Proceeding and duration of spermatogenic cycle in the ram). Ann. Zootech., 4, 271-321. Pelletier, J., Chemineau, P. and Delgadillo, J.A., 1988. Seasonality of sexual activity and its photoperiodic control in the adult ram and he-goat. In: Proc. 1 lth Inter. Congr. Anim. Reprod. Artif. Insem., Dublin, 5, pp. 211-219. Snedecor, G.W. and Cochran,. W.C., 1980. Statistical Methods. 7th edition, The Iowa State University Press, Ames, pp. 507. RI~SUMI~ Delgadillo, J.A., Leboeuf, B. and Chemineau, P., 1992. Abolition des variations saisonni6res de la qualit6 de la semence et maintien de la f6condance par des cycles photop6riodiques acc616r6s chez le bouc. SmallRumin. Res., 9: 47-59. Les boucs pr6sentent des variations saisonni6res importantes de leur qualit6 spermatique, essentiellement sous l'influence des changements photop6riodiques. Le pourcentage de spermatozo'ides mobiles et la motilit6 sont minimas au printemps et en 6t6. Trois groupes de boucs Alpins et Saanen (6 animaux dans chaque groupe) sont utilis6s pour d6terminer si des alternances rapides entre des jours courts et des jours longs sont capables d'abolir les variations saisonni~res de la qualit6 de la semence. Un groupe (An) reste dans un b~timent ouvert et per~oit les variations naturelles de la photop6riode qui varie de 16 heures (juin) h 8 heures

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(d6cembre) de lumi~re par jour. Le premier groupe exp6rimental (2Mo) est soumis/t des alternances entre un mois de jours longs (16L:8D) et un mois de jours courts (8L:I6D) et le second/l des alternances entre deux mois de jours longs et deux mois de jours courts, pendant deux ann6es cons6cutives. Tousles param6tres de qualit6 de la semence avant et apr6s cong61ation varient avec le temps dans les trois groupes ( P < 0,0001 ). Une interaction entre le groupe et le mois est 6galement d6tect6e pour 4 param~tres sur 6 ( P < 0.05), ce qui indique que les groupes ne suivent pas la m~me 6volution au cours des mois. Aucun effet ann6e, ni d'interaction ann6e-groupe n'est mis en 6vidence. La qualit6 de la semence dans les groupes exp6rimentaux n'est pas affect6e par la photop6riode en cours. Comme attendu, dans le groupe An, le pourcentage de spermatozo'ides mobiles et la note de motilit6 (0-5) avant et apr6s d6gel diminuent en dehors de la saison sexuelle (mars/l ao~t; m i n m u m en aoflt: 37.8% et 2,4 avant cong61ation) par rapport/l la saison sexuelle (septembre/~ f~vrier; maximum en janvier: 66,3% et 3,6 avant cong61ation). La production de doses de semence disponibles pour I'I.A. diminue 6galement pendant cette p6riode. Au contraire, dans les deux groupes exp6rimentaux la diminution de qualit6 de semence pendant cette p6riode est 6vit6e. Dans ces groupes, le pourcentage de spermatozo'ides mobiles et la motilit6 de la semence avant et apr6s cong61ation restent au niveau de ceux du lot An pendant la saison sexuelle. L'abolition des variations saisonni6res de la qualit6 de la semence conduit/l produire 69,0 et 54,7% de doses d'I.A, en plus dans les groupes 2Mo et 4Mo que dans le groupe An. La fertilit6 de la semence des trois groupes n'est pas significativementdiff6rente (59.4% de mise bas pour 1599 ch6vres appartenant/~ 58 troupeaux). I1 est conclu que chez le bouc, des alternances de jours courts et de jours longs abolissent les variations saisonni6res de qualit6 de semence sans alt6rer sa fertilit6.

RESUMEN Delgadillo, J.A., Leboeuf, B. and Chemineau, P., 1992. Supresi6n de las variaciones estacionales de la calidad del semen y conservaci6n de la fertilidad por ciclos fotoperiodicos en el macho cabrio. SmallRumin. Res., 9: 47-59. Los machos caprinos presentan importantes variaciones estacionales de la calidad del semen provocadas principalmcnte por los combios fotoperi6dicos. El porcentaje de espermatozoides m6viles y su velocidad de desplazamiento son minimos durante la primavera y el verano. Tres grupos de machos Alpinos y Saanen (6 animales por grupo) fueron utilizados para determinar si las alternancias nipidas de dias cortos y dias largos son capaces de abolir las variaciones estacionales de la calidad del semen. U n grupo (An) rue alojado en instalaciones abiertas y percibi6 las variaciones naturales del fotoperiodo quc oscilan entre 16 horas (junio) y 8 horas (diciembre) de luz por dia. E1 primer grupo experimental (2Mo) rue sometido alternativamente a un mes de dias largos ( 16L: 8D ) y un mes de dias cortos (8L: 16D) y el segundo (4Mo) a dos meses de dias largos y dos meses de dias cortos, durante dos afios consecutivos. En los tres grupos se observaron variaciones significativas ( P < 0,0001 ) de la calidad del semen con respecto al tiempo. En 5 de los 6 parfimetros evaluados para determinar la calidad del semen hubo interacci6n significativa ( P < 0,05 ) entre grupo y mes, lo que indica que la variaci6n mensual de la calidad del semen fue diferente entre los grupos. No se observ6 efecto del afio ni interacci6n afio-grupo. La calidad del semen en los grupos experimentales no rue afectada por el fotoperiodo prevalente. En el grupo An, el poreentaje de espermatozoides m6viles y la velocidad de desplazamiento (0-5) antes y despu6s de la descongelaci6n disminuyeron fuera de la estaci6n sexual (de marzo a agosto; minimo en agosto: 37,8% y, 2,4 antes de la congelaci6n) en comparaci6n con la estaci6n sexual (de septiembre a febrero; mfiximo en enero: 66,3%

SEMENQUALITYANDMAINTENANCEOF SPERMFERTILIZINGABILITYBYPHOTOPERIODICCYCLES 59 y 3,6 antes de la congelaci6n). La producci6n de dosis de semen disponibles para la I.A. disminuy6 igualmente durante el periodo de resposo sexual. Por el contrario, en los dos grupos experimentales, la disminuci6n de la calidad del semen durante este periodo fue evitada. En estos grupos, el porcentaje de espermatozoides m6viles y la velocidad de desplazamiento de los espermatozoides antes y despu6s de la congelaci6n permanecieron similares que los del lote An durante la estaci6n sexual. La abolici6n de las variaciones estacionales de la calidad del semen permiti6 a los grupos 2Mo y 4Mo producir 69,0 y 54,7% m~is dosis de semen para la I.A. que el grupo An. La fertilidad del semen de los tres grupos no fue significativamentediferente ( 59.4% de partos en 1599 cabras pertenecientes a 58 explotaciones). Se concluye q u e e n el macho cabrio, las alternancias r~lpidas de dias cortos y dias largos suprimen las variaciones estacionales de la calidad del semen sin alterar su fertilidad.