Seasonal variation in reproductive physiological status in the Iberian ibex (Capra pyrenaica) and its relationship with sperm freezability

Equilibration time improves the sperm variables of wild ruminant ejaculated and epididymal sperm cryopreserved by ultra-rapid freezing

This work examines the effect of equilibration time with extender on ultra-rapidly frozen-thawed wild ruminant epididymal (origin: Iberian ibex) and ejaculated (origin: mouflon) sperm variables. Sperm samples were prepared either without prior equilibration, or equilibrated for 30 min before freezing. Higher quality (p < 0.05) frozen-thawed spermatozoa were obtained when equilibration was allowed, for ejaculated sperm in terms of sperm motility, acrosome apical ridge integrity, sperm viability, and percentage of normal cells, and for epididymal sperm in terms of linearity and straightness of sperm movement. The sperm head area, head perimeter, head length and head width were smaller (p < 0.01) in the equilibrated than non-equilibrated frozen-thawed epididymal sperm; no such dimensional changes were recorded for ejaculated sperm. In conclusion, equilibration prior to ultra-rapid freezing improves the cryoresistance of sperm cells, although viable sperm cells can be obtained without equilibration. The epididymal sperm showed greater cryoresistance, supporting the idea that it is more resistant to freeze-thawing than ejaculated sperm.

Single or repeated immunization against GnRH fails to completely abolish spermatogenesis in dwarf bucks (Capra hircus)

In both captive wildlife and production animals is important to develop strategies for population control. Immunization against GnRH is an easy and inexpensive immunocastration method that reduces the concentration of testosterone and decreases sperm quality. However, its effectiveness depends on the species and repetition of the treatment. This study aimed to compare the effectiveness of a single treatment (initial immunization plus a booster with Improvac) vs repeated treatment (six doses of Improvac) to inhibit testicular function and maintain the contraceptive status during long periods in bucks. Three Dwarf bucks (Capra hircus) received two doses of Improvac, the first on Week 0, and the booster 4 weeks later (single immunization, group SI) while three Dwarf bucks received one dose of Improvac every 6 months during 3 consecutive years (repeated immunization, group RI). The other three Dwarf bucks remained untreated (control bucks, group CON). Bucks from RI had a greater decrease in scrotal circumference, testosterone concentration, male odor intensity, and sperm quality than SI bucks. However, there were no differences between SI and CON bucks in any of the variables studied. Overall, repeated treatment of Improvac decreased the testicular function of Dwarf bucks, although did not produce complete infertility. However, the repetition of the treatment produced more intensive negative effects, indicating that the strength of the effects of Improvac is rapidly lost in bucks.

Expression of Aquaglyceroporins in Spermatozoa from Wild Ruminants Is Influenced by Photoperiod and Thyroxine Concentrations

This work identified the presence of AQPs in frozen-thawed sperm of wild ruminants and assessed the influence of the interaction between photoperiod and thyroxine on AQP expression, and on testosterone secretion. Thyroxine and melatonin were administered to ibexes. In a second experiment, performed in mouflons, circulating thyroxine was reduced via treatment with propylthiouracil (PTU), and an artificial long day (LD) photoperiod established. In the ibexes, the melatonin treatment increased the blood plasma testosterone concentration, reduced the cryoresistance ratio (CR) for sperm viability and the presence of an intact acrosome, and increased the percentage of sperm with AQP7 in the acrosome and of AQP3 and AQP10 in the midpiece. In the mouflons, neither the PTU treatment, the LD, nor the combination of both affected the CR of any sperm variable. The percentage of sperm with AQP3 increased in the post-acrosome region but decreased in the tail in the LD+PTU group. The percentage of sperm with AQP10 in the principal piece and endpiece was lower in the PTU+LD group than in the control and LD groups. The influence of photoperiod/melatonin on AQP expression might be indirectly exerted through changes in the testosterone concentration, and thus ultimately affect sperm cryoresistance.

The Re-Addition of Seminal Plasma after Thawing Does Not Improve Buck Sperm Quality Parameters

Simple Summary

The Cabra Blanca de Rasquera is a native goat breed from Catalonia (Spain) facing the danger of extinction. To preserve its genetic diversity, ex situ conservation programs for semen cryopreservation and the development of a genetic sperm bank are of major importance. However, the post-thaw sperm quality in this species is still a major concern. Therefore, the aim of this research work was to establish an approach in the thawing protocol of cryopreserved sperm bank doses of this breed in order to achieve a better post-thaw sperm quality and improve reproductive outcomes through artificial insemination. Since seminal plasma has been found to provide a source of nutrients, improve sperm motility, and prevent premature activation during migration of spermatozoa in the female reproductive tract, our study proposed to assess the effect of the addition of 20% seminal plasma (SP) during a 3 h incubation period under in vitro conditions mimicking the in vivo survivability of thawed sperm, in relation to donor age, the season of collection, and melatonin implants of the males in the non-breeding season. However, the strategy of adding seminal plasma to the sperm after thawing failed to improve buck post-thawed sperm quality, thus further investigation is needed.

Abstract

In order to achieve a higher post-thaw buck sperm quality, an approach in the thawing protocol of cryopreserved sperm doses under in vitro capacitation conditions mimicking the in vivo female environment was studied. Therefore, functional and kinetic characteristics of buck thawed sperm from males of different ages, the season of collection, and melatonin implanted males in the non-breeding season were assessed after 3 h of incubation in an in vitro fertilization (IVF) media with 20% of buck seminal plasma (SP). Previously, fresh ejaculates were collected via artificial vagina from eight males of the Cabra Blanca de Rasquera breed during two consecutive years in breeding and non-breeding periods. Prior to semen collection in non-breeding seasons, males were split into two groups: one group was implanted with melatonin, while the other was not. In each group, semen samples were pooled, centrifuged, and diluted in an extender containing 15% powdered egg yolk and 5% glycerol before freezing. After thawing, sperm were washed and incubated in three different media: (a) control media (modified phosphate-buffered saline (PBS), (b) IVF commercial media, and (c) IVF media + 20% SP. Sperm motility was evaluated by CASA, while plasma and acrosome membrane integrity, mitochondria activity, and DNA fragmentation were analysed by flow cytometer at 0 h and after 3 h incubation. A significant reduction in motility, mitochondrial activity, plasma, and acrosome membrane integrity were observed after incubation in the presence of SP, although similar to that observed in IVF media alone. DNA integrity was not affected under in vitro capacitation conditions, regardless of SP addition. In conclusion, the addition of SP failed to improve post-thaw buck sperm quality under in vitro conditions irrespective of male age, the season of collection, and melatonin implant.

Relationship between the seasonal changes in plasma testosterone and thyroxine concentrations with sperm cryoresistance in Gabon bucks

Gabon buck is a breed with little marked seasonality in our latitude (Uruguay, 35° SL). The role of thyroid hormones on the regulation of their seasonal reproductive activity and sperm cryoresistance is unknown. Seasonal changes in testosterone concentration can affect sperm variables, but the influence of testosterone changes on sperm cryoresistance in other species determines that the recommended time for freezing sperm does not coincide with the period with greater sperm fresh quality. The objectives of the present work were to (i) describe the thyroxine seasonal pattern in bucks in a subtropical area, and its association with annual changes in sperm variables; (ii) relate the seasonal changes of testosterone and thyroxine concentrations with the sperm cryoresistance. For one year, semen of 10 adult Gabon bucks was collected by electroejaculation every two weeks. After sperm selection, the sample was frozen. Testosterone and thyroxine concentrations varied according to the month (P < 0.0001). Testosterone reached the greatest values in April (P < 0.0001) and May (P < 0.0001) and thyroxine reached minimum values (P < 0.0001) in the same months. During these months, a negative correlation ratio (CR) was found between testosterone concentration and CR-functional membrane (R =  - 0.50; P < 0.0001). CR values for most sperm variables decreased during March-May, coinciding with the presence of maximum testosterone concentrations. In conclusion, high testosterone levels are associated with the worst sperm response to freezing-thawing process. Thyroxine concentrations have a strong seasonal pattern, but there was no relationship to sperm cryoresistance.

Using transrectal ultrasound-guided massage of the accessory sex glands for buck semen collection yields semen with greater cryoresistance than electroejaculation alone during the breeding season

The cryoresistance of bucks' semen collected by transrectal ultrasound-guided massage of the accessory sex glands (TUMASG) and electroejaculation (EE) was compared during the breeding season (Study 1) or the late non-breeding season (Study 2). Semen was collected from 10 Gabon bucks with both methods in each season and then frozen according to a standardized protocol. The time required for ejaculation, the number of electrical pulses applied, the sum of the electrical pulses applied∗voltage and the total number of vocalizations emitted during the collection by each animal were recorded. In Study 1, TUMASG required a longer time (P = 0.0006) but fewer electrical pulses and a lower sum of pulses∗voltage than EE (P < 0.0001 for both comparisons). Bucks vocalized fewer times during TUMASG than during EE (P < 0001). Semen collected with TUMASG had greater sperm concentration, sperm mass motility, total number of motile sperm and of sperm with progressive motility, and tended to have greater total number of sperm with functional membrane than semen collected with EE (P = 0.02; P = 0.003; P = 0.02; P = 0.02; P = 0.06, respectively). After the freezing-thawing process, sperm collected with TUMASG had a greater quality of the motility, a total number of motile sperm and sperm with progressive motility, a greater percentage of motile sperm and sperm with functional membrane, and tended to have a greater total number of sperm with normal morphology than semen collected with EE (P = 0.04; P = 0.04; P = 0.03; P = 0.02; P = 0.04; P = 0.06, respectively). In Study 1 sperm collected with TUMASG had greater cryoresistance for almost all the variables considered than when it was collected with EE. In Study 2, the number of electrical pulses and the sum of pulses∗voltage were greater with EE than with TUMASG (P < 0001; P = 0.0002, respectively). There were no differences in any sperm variable in fresh or thawed samples collected with TUMASG or EE. However, the other seminal characteristics evaluated did not differ according to the method, and there were no differences in the cryoresistance of any variable. Overall, TUMASG affected animal welfare less than EE and was suitable for collecting semen of good quality with high cryoresistance during the breeding season in buck.

Effect of Season and Social Environment on Semen Quality and Endocrine Profiles of Three Endangered Ungulates (Gazella cuvieri, G. dorcas and Nanger dama)

Knowledge of factors affecting semen quality could be of great importance for the collection and preservation of semen from threatened animals. To assess the effect of seasonality, sperm parameters and testosterone levels were examined throughout the year and compared with the distribution of conceptions. Cuvier's gazelle showed higher sperm quantity in April, coinciding with one peak of conceptions. In dorcas gazelle, sperm parameters showed a drop in October. However, percentage of conceptions increased during that month. In Mohor gazelle, sperm quality was best in April and August, in agreement with higher conception rates and high testosterone levels. Percentage of conceptions was correlated with photoperiod and rainfall in Cuvier's gazelle and with temperature in Mohor gazelle. To assess the effect of social environment, semen quality, testosterone and cortisol levels were quantified in males housed alone, in bachelor groups or with females. No differences were seen in Cuvier's and Mohor gazelles' semen traits, whereas dorcas males housed with females showed lower semen quality than males kept alone or with other males. Overall, ejaculate quality is influenced by seasonal factors in the three gazelle species, while social factors only appear to affect that of dorcas gazelle.

Influence of circulating testosterone concentration on sperm cryoresistance: The ibex as an experimental model

BACKGROUND

Recent studies have noted that the circulating testosterone concentration may affect the ability of spermatozoa to survive cryopreservation. However, few attempts to confirm such a relationship have been made. Wild ruminant species have very marked seasonal changes in their reproductive function and strong annual changes in their plasma testosterone concentration.

OBJECTIVES

The present work examines the influence of induced changes in testosterone secretion on sperm variables following conventional slow freezing and ultra-rapid freezing, using the Iberian ibex as an experimental model.

MATERIALS AND METHODS

In a first experiment, testosterone levels were reduced in the middle of the rutting season (December) using the antiandrogen cyproterone acetate (CA). In a second experiment, testosterone levels were increased at the end of the rutting season (January) via the use of the androgen testosterone propionate (TP).

RESULTS

During December, the testosterone concentration was found to be higher in the blood and seminal plasma of untreated males than in those of CA-treated males (p < 0.001 and p < 0.05, respectively). Compared with controls, the TP-treated animals had higher blood plasma testosterone concentrations but lower seminal plasma testosterone concentrations during January (p < 0.01 and p < 0.001, respectively). The seminal vesicles of the TP-treated males were larger than those of untreated males (p < 0.05). When CA was administered, sperm viability improved compared with controls (p < 0.05), irrespective of the freezing protocol followed. For the ultra-rapid freezing procedure, the cryoresistance ratio for motility decreased when TP was administered (p < 0.05). The values for fresh sperm morphometric variables decreased during the 50 days after the end of CA treatment (p < 0.001) and increased over the same time after the end of TP treatment (p < 0.001).

DISCUSSION AND CONCLUSION

The circulating testosterone concentration appears to influence sperm cryoresistance. This may explain the seasonal changes seen in sperm freezability in some species, independent of fresh sperm quality.

Influence of testosterone administration at the end of the breeding season on sperm cryoresistance in rams (Ovis aries) and bucks (Capra hircus)

This study examines the influence of administering testosterone at the end of the mating season, on the responses (morphometric and functional) of ram and buck sperm to freezing-thawing. Five rams were administered 25 mg testosterone propionate (TP) subcutaneously in 2 mL of olive oil twice per week (Monday and Thursday) from October 1 to 31; 5 bucks received exactly the same treatment but from November 1 to 30. Control groups were administered 2 mL of olive oil without TP twice per week over the same period. In the rams, no significant differences were seen in plasma testosterone between the treated and control groups during treatment (0.8 ± 0.2 ng/mL vs 1.5 ± 0.5 ng/mL; P > 0.05). Significant differences were seen in this respect, however, in the bucks (4.3 ± 0.8 ng/mL and 6.9 ± 0.9 ng/mL; P < 0.05). In the rams, TP treatment increased (P < 0.05) the straight-line velocity (VSL), linearity (LIN), straightness (STR) and wobble (WOB) values in fresh sperm samples. Similarly, in the frozen-thawed samples, TP treatment increased the VSL, average path velocity (VAP), LIN and WOB values (P < 0.05) compared with controls. In the bucks, treatment with TP had no effect on any measured variable in fresh sperm; frozen-thawed sperm, however, returned greater VSL, LIN, STR, and WOB values (P < 0.05) than did controls. In the rams, treatment with TP led to a reduction in all fresh sperm head morphometric variables (P < 0.05). Freezing-thawing further reduced (P < 0.05) all morphometric variables in both the control and treated groups. In the bucks, treatment with TP increased (P < 0.05) the length, area, and perimeter of fresh sperm cells, unlike that seen in ram sperm. Compared with fresh sperm, freezing-thawing led to reduced (P < 0.05) morphometric variables in both the control and treated bucks, except for the sperm head width, which in the controls remained unchanged. In conclusion, TP treatment at the end of the mating season affected fresh sperm quality, in both Spanish Merino rams and Murciano-Granadina bucks, in a species-specific manner, but improved the sperm kinetic variables after freezing-thawing in both species, apparently improving sperm cryoresistance. Treatment with TP affects the dimensions of the sperm head in a species-specific manner.

In vitro supplementation of testosterone or prolactin affects spermatozoa freezability in small ruminants

In small ruminants, testosterone and prolactin plasma concentrations show circannual fluctuations as an adaptation mechanism to their seasonal breeding behavior. Sperm resistance to the freezing-thawing process shows seasonal fluctuation throughout the year, with lower sperm freezability at the beginning of the breeding season when prolactin and testosterone levels reach their maximum concentration. Nevertheless, whether these hormones directly affect post-thaw sperm quality parameters is still unclear. The objective was to study the effect of testosterone or prolactin added in vitro on sperm freezability in domestic ram (Ovis aries) and buck (Capra hircus). Sperm samples were incubated for 1 h with a range of testosterone (0, 2, 4, or 6 ng/mL; Exp. 1) or prolactin (0, 20, 100, 200, or 400 ng/mL; Exp. 2) concentrations. Samples were cryopreserved by slow freezing in straws at 0 h and after 1 h incubation. Sperm viability, acrosome integrity, motility, and kinetic parameters were assessed at 0 and 1 h in fresh and frozen-thawed samples. Results showed no hormone effect in fresh sperm, whereas these hormones affected post-thaw sperm parameters. In Exp. 1, in vitro incubation with testosterone decreased the post-thaw acrosome integrity of ram sperm (from 68.1 ± 6.3% to 49.6 ± 3.9%; P < 0.05). In Exp. 2, in vitro incubation with prolactin decreased the post-thaw acrosome integrity of ram (from 78.2 ± 3.4% to 66.3 ± 3.5%; P < 0.05) and buck sperm (from 81.7 ± 2.5% to 67.6 ± 3.5%; P < 0.05). Moreover, prolactin increased the post-thaw amplitude of lateral head displacement in ram sperm (from 3.3 ± 0.1 μm to 3.8 ± 0.2 μm; P < 0.05). In conclusion, either testosterone or prolactin added in vitro decreased the post-thaw acrosome integrity of ram and buck sperm. This suggests a destabilization process that could be decreasing sperm freezability when physiological levels of these hormones are high in vivo.

Ultra-rapid cooling of ibex sperm by spheres method does not induce a vitreous extracellular state and increases the membrane damages

Sperm cryopreservation by ultra-rapid cooling based on dropping small volumes of sperm suspension directly into liquid nitrogen, has been successful in some wild ruminant species, including the Iberian ibex (Capra pyrenaica). In ultra-rapid cooling, the contents of these droplets are expected to enter a stable, glass-like state, but to the best of our knowledge no information exists regarding the presence or absence of ice formation in the extracellular milieu when using this technique. Different modifications to the extracellular milieu likely inflict different types of damage on the plasmalemma, the acrosome and mitochondrial membranes. The aims of the present work were: 1) to examine the physical state of the extracellular milieu after cryopreservation at slow and ultra-rapid cooling rates—and thus determine whether ultra-rapid cooling vitrifies the extracellular milieu; and 2) to compare, using conventional sperm analysis techniques and scanning and transmission electron microscopy, the damage to sperm caused by these two methods. Sperm samples were obtained by the transrectal ultrasound-guided massage method (TUMASG) from anesthetized Iberian ibexes, and cryopreserved using slow and ultra-rapid cooling techniques. Sperm motility (22.95 ± 3.22% vs 4.42 ± 0.86%), viability (25.64 ± 3.71% vs 12.8 ± 2.50%), acrosome integrity (41.45± 3.73% vs 27.00 ± 1.84%) and mitochondrial membrane integrity (16.52 ± 3.75% vs 4.00 ± 0.65%) were better after slow cooling (P<0.001) than after ultra-rapid technique. Cryo-scanning electron microscopy (Cryo-SEM) suggested that the vitrified state was not achieved by ultra-rapid cooling, and that the ice crystals formed were smaller and had more stretchmarks (P<0.001) than after slow cooling. Scanning electron microscopy revealed no differences in the types of damage caused by the examined techniques, although transmission electron microscopy showed the damage to the plasmalemma and mitochondrial membrane to be worse after ultra-rapid cooling. In conclusion ultra-rapid cooling provoked more membrane damage than slow cooling, perhaps due to the extracellular ice crystals formed.

Seasonal variation in sperm freezability associated with changes in testicular germinal epithelium in domestic (Ovis aries) and wild (Ovis musimon) sheep

The aim of this study was to examine ovine sperm cryoresistance during the rutting season (RS) and its association with sperm head area and seminiferous epithelium proliferation. Small ruminants show fluctuating testosterone levels throughout the year, which could interfere with spermatogenesis and sperm cryopreservation. Ejaculates, testicular biopsies and blood were collected during the middle and at the end of the RS (Middle-RS vs End-RS) during periods of high and low testosterone levels in Merino and Mouflon rams. Fresh and frozen–thawed sperm quality, sperm morphometry, seminiferous tubule morphometry and testicular proliferation markers (proliferating cell nuclear antigen, proliferation marker protein Ki-67 and transcription factor GATA-4) were evaluated. Post-thaw sperm viability was higher in the End-RS group in both Merino (69.9±8.2 vs 41.6±7.3%; P=0.020) and Mouflon rams (40.9±3.3 vs 24.2±5.0%; P=0.008). Mouflons had larger sperm head area at the End-RS (38.3±0.2 vs 34.3±0.1µm2; P=0.029), whereas there was no difference between Merino groups (35.7±0.5 vs 34.8±1.0µm2). Seminiferous tubule morphometry and proliferation markers showed higher levels of germinal epithelium proliferation in the Middle-RS of both species. In conclusion, sperm freezability is affected during the RS in domestic and wild rams, which could be correlated with changes that occur during spermatogenesis, since there is an effect of season on cell proliferation in the testis.

Milk proteins interact with goat Binder of SPerm (BSP) proteins and decrease their binding to sperm

Seminal plasma Binder of SPerm (BSP) proteins bind to sperm at ejaculation and promote capacitation. When in excess, however, BSP proteins damage the sperm membrane. It has been suggested that milk components of semen extenders associate with BSP proteins, potentially protecting sperm. Thus, this study was conducted to investigate if milk proteins interact with BSP proteins and reduce BSP binding to goat sperm. Using gel filtration chromatography, milk was incubated with goat seminal plasma proteins and loaded onto columns with and without calcium. Milk was also fractionated into parts containing mostly whey proteins or mostly caseins, incubated with seminal plasma proteins and subjected to gel filtration. Eluted fractions were evaluated by immunoblot using anti-goat BSP antibodies, confirming milk protein-BSP protein interactions. As determined by ELISA, milk proteins coated on polystyrene wells bound to increasing of goat BSP proteins. Far-western dot blots confirmed that BSP proteins bound to caseins and β-lactoglobulin in a concentration-dependent manner. Then, cauda epididymal sperm from five goats was incubated with seminal plasma; seminal plasma followed by milk; and milk followed by seminal plasma. Sperm membrane proteins were extracted and evaluated by immunoblotting. The pattern of BSP binding to sperm membrane proteins was reduced by 59.3 % when epididymal sperm were incubated with seminal plasma and then with skimmed milk (p < 0.05). When epididymal sperm were treated with milk followed by seminal plasma, coating of sperm with BSP proteins was not significantly reduced (57.6 %; p > 0.05). In conclusion, goat BSP proteins have an affinity for caseins and whey proteins. Milk reduces BSP binding to goat sperm, depending whether or not sperm had been previously exposed to seminal plasma. Such events may explain the protective effect of milk during goat sperm preservation.

Fertilization capacity of cryopreserved Iberian ibex epididymal sperm in a heterologous in vitro fertilization assay

In vitro fertilization (IVF) can be used to assess the fertilization capacity of sperm. Heterologous IVF may be useful when assessing that of wild animals as it is often difficult to obtain adequate numbers of naturally corresponding oocytes. The aim of the present study was to assess the fertilization capacity of frozen–thawed ibex epididymal spermatozoa via heterologous IVF involving the oocytes of prepubertal domestic goats. The effect on fertilization and embryo development of adding oestrous sheep serum (ESS) to the fertilization medium was also examined. Cumulus–oocyte complexes (COCs) were matured in TCM-199 for 24–27 h at 38.5°C in a 5% CO2 in air atmosphere. Frozen–thawed epididymal spermatozoa were selected by density gradient centrifugation. After maturation, the oocytes were co-incubated with spermatozoa in synthetic oviductal fluid (SOF) with different concentrations of ESS: SOF-C (0%), SOF-2 (2%) and SOF-20 (20%). At 17 h post-insemination (hpi), zygotes with one female and one male pronucleus (2PN) were categorised as normal; zygotes with 3PN were recorded as polyspermic, and oocytes with 1PN as asynchronous. Cleavage and blastocyst development were assessed at 48 and 168 hpi respectively. The percentage of zygotes with 2PN was higher in the SOF-2 than in the SOF-20 treatment group (27.7% versus 2.9% P < 0.05). The percentage of blastocysts formed with the SOF-C, SOF-2 and SOF-20 treatments were 1.1%, 7.5% and 0% respectively. These results show that the presence of 2% ESS achieves better results than the use of no serum or the standard 20% concentration. Heterologous IVF may be an effective method for predicting the fertilization capacity of ibex spermatozoa, and therefore perhaps that of other wild mountain ungulates.

Photoperiod and melatonin treatments for controlling sperm parameters, testicular and accessory sex glands size in male Iberian ibex: A model for captive mountain ruminants

This study examines whether photoperiod and/or melatonin treatments can improve sperm variables outside the breeding season in the Iberian ibex-a model species for wild mountain ruminants-thus helping in the collection of high quality sperm beyond the normal breeding season for depositing in genetic resource banks. Adult Iberian ibex males (n=17) were divided into four treatment groups: (1) controls under the natural photoperiod (control group; n=4), (2) treatment with melatonin implants on December 22nd, February 22nd and April 22nd (group WS-M; n=5), (3) treatment with short photoperiod cycles, i.e., 2 months of long days followed by melatonin implants (to emulate 2 months of short days) throughout the year (group PHPld+M; n=4), and (4) treatment with melatonin implants on June 22nd and August 22nd (group SS-M; n=4). The interaction treatment x season had a strong influence on testis size (P<0.05), the size of the seminal vesicles (P<0.001), the percentage of abnormal sperms (P<0.05), and percentage non-progressive (P<0.05) and progressive (P<0.001) sperm motility. In groups WS-M and PHPld+M, the normal springtime physiological reductions in testis size, non-progressive sperm motility and acrosome integrity were prevented. The values for the studied sperm variables were, however, reduced in the natural breeding season at the end of the experimental period in group PHPld+M, although not in group WS-M. The pattern of melatonin administration in group SS-M conferred no advantages on reproductive functionality. These results suggest that lengthening the short day period after the winter solstice (the WS-M treatment) extends reproductive activity in this species, allowing good quality sperm to be recovered for conservation purposes during the non-breeding season.