Seasonal variations in the composition of ram seminal plasma and its effect on frozen-thawed ram sperm

Ram Semen Cryopreservation for Portuguese Native Breeds: Season and Breed Effects on Semen Quality Variation

The semen quality is one of the determinant factors of ram semen cryopreservation. The present retrospective study aimed to characterize the seasonal ram pattern during the year for ten Portuguese local sheep breeds, hypothesizing that the breed and season had low effects on the main spermatozoa traits. A total of 1471 ejaculates were used and evaluated (fresh semen) from 85 rams between 2004 and 2020 and re-evaluated after thawing (thawed semen). The effect of breed, season, and sperm cryopreservation on nine semen traits were evaluated. The volume per ejaculate, spermatozoa (SPZ) concentration, and total number of SPZ per ejaculate, were affected by breed (p < 0.001) but not by season (p > 0.05). As expected, the semen processing was the most significant (p < 0.001) factor of variation on seminal parameters. Moreover, breed and interactions between breed × semen processing, modulated the response of alive SPZ, abnormal morphology, head, and intermediate piece defects. In fresh semen, season only affected the intermediate piece defects due to the highest percentage observed between February and April period in some breeds. Overall, and despite the mentioned particularities, there were similarities among the ten local breeds. We also concluded that the seasonal effect on ejaculate and SPZ traits is not significant in our region. These local ram breeds have low seasonality and can be employed in natural mating as well as semen donors for cryopreservation and assisted reproductive biotechnologies during the whole year at our latitude.

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.

Effects of Three Semen Extenders, Breeding Season Month and Freezing-Thawing Cycle on Spermatozoa Preservation of Portuguese Merino Sheep

Simple Summary

Spermatozoa (SPZ) viability, morphology and the kinetics of fresh and thawing Portuguese Merino Semen were evaluated at different breeding season months using an owner egg yolk-based semen extender (S-EXT) and two commercial lecithin-based semen extenders. The main significant differences between S-EXT were observed for thawed semen. The viability (30% vs. 15% of alive SPZ; p < 0.001), total motility (74% vs. 34%; p < 0.001), total progressive motility (18% vs. 5%; p < 0.001), straight line velocity (37 vs. 22 μm/s; p < 0.001) and beat cross frequency (13 vs. 6 Hz; p < 0.05) were higher in the owner egg yolk than in egg yolk-free-based S-EXT. Significant interactions between S-EXT, semen processing and/or months of semen collection were observed on several of the 22 evaluated SPZ parameters and should be elucidated in further studies. The egg yolk-based S-EXT was more consistent across the months in cryopreserving SPZ than commercial egg yolk- free-based S-EXT and still seems, to the present day, the most appropriate S-EXT to be used in (Merino) sheep.

Abstract

This study aimed to evaluate and compare the effect of three semen extenders (S-EXT) on 22 spermatozoa (SPZ) parameters (subjective and computer-assisted sperm analysis evaluations), before and after semen cryopreservation throughout different months of the breeding season in the Portuguese Merino breed. According to the multivariable model, the SPZ viability (alive %), kinetics subjective individual motility, total motility, total progressive motility and its subpopulations, and beat cross frequency) were higher in the egg yolk-based S-EXT improved by Estação Zootécnica National (Portugal) than in Ovixcell^® or Andromed^® extenders. All the differences were only observed in thawed semen, except for total motility and total progressive motility, in which Ovixcell^® also showed the poorest results on fresh semen. An interaction effect between S-EXT and semen processing was observed on 72.3% (17/22) of the evaluated parameters, evidencing a variable cryoprotective action between S-EXT. The SPZ viability was poorer in the onset of the breeding season (end of April/early May) than in the previous middle breeding season (November/early December), suggesting the influence of a short anoestrous season on ejaculate quality, even though the volume and SPZ concentration of the ejaculates remained stable throughout the experiment. Additionally, S-EXT x semen processing x month interaction effect on 59.1% (13/22) of the evaluated parameters evidenced the importance of SPZ time collection in a natural environment to cryopreserve ram’s semen. We concluded that, overall, the egg yolk-based S-EXT provided a greater value to the cryopreservation of Merino rams´ semen. Nevertheless, the causes of the interaction effect between S-EXT, semen processing and/or month on several SPZ parameters should be addressed, including SPZ molecular research in new studies, in order to improve egg yolk-based as well as in egg yolk-free-based S-EXT.

Organic mineral supplementation on differential protein profile of Osmanabadi bucks (Capra hircus)

The present study aimed to determine the differential protein profile of seminal plasma proteins of bucks supplemented with trace minerals. Forty bucks of uniform size and body weight were assigned as ten groups (n = 4). The control group (T1) was fed with the control diet (concentration mixture and roughages) whereas the remaining groups were supplemented the control diet with Zn20 mg (T2), Zn40 mg (T3), Zn60 mg (T4), Cu12.5 mg (T5), Cu25 mg (T6), Cu37.5 mg (T7), Zn20 mg + Cu12.5 mg (T8), Zn40 mg + Cu25 mg (T9), and Zn60 mg + Cu37.5 mg (T10) for eight months. Seminal plasma proteins from each group were subjected to two-dimensional electrophoresis and fifteen differential proteins were selected based on differential expression, subjected to identification using Nano-LC-MS/MS (LTQ-Qrbitrap-MS). The identified proteins were Triacylglycerol lipase, EGF like repeats and discoidin domains 3, Lipocalin, Iodothyronine deiodinase, Transcription factor AP2-delta, 60S ribosomal protein L13, IST1 factor associated with ESCRT-III, Lysozyme, Uncharacterized protein (BRI3-binding protein), Uncharacterized protein, Histone deacetylase 11, General transcription factor IIF subunit 2, Nudix hydrolase 6, Protein kinase cAMP-activated catalytic subunit beta and Elongin C. The organic Cu supplemented group is the better than the organic Zn and organic Zn + Cu supplemented groups.

Trehalose modifies the protein profile of ram spermatozoa during cryopreservation

As a magical oligosaccharide, trehalose has been revealed to enhance the post-thaw quality of stock semen. However, information regarding the cryoprotective mechanism of trehalose during cryopreservation has not yet been determined. This study was designed to observe the effects of trehalose on the proteome of ram frozen spermatozoa by applying the isobaric tag for relative and absolute quantification (iTRAQ) strategy combined with parallel reaction monitoring (PRM). A total of 1269 proteins were identified. Among them, there were 21 differentially expressed proteins (DEPs), with 9 up-regulated proteins and 11 down-regulated proteins in spermatozoa frozen with trehalose. These DEPs were primarily located in nucleus, cytoplasm, and extracellular region. The Gene Ontology (GO) enrichment analysis demonstrated the involvement of the DEPs in signal transduction, ion binding, oxidoreductase activity, response to stress, and catabolic processes. Based on the STRING analysis, tight functional correlations were observed between 6-phosphogluconate dehydrogenase, fructose-bisphosphate aldolase A isoform 1, 14-3-3 protein epsilon, tyrosine-protein kinase Fer, and beta-hexosaminidase subunit alpha precursor. Furthermore, 10 DEPs were verified using PRM, confirming the accuracy of the iTRAQ data acquired in this study. In conclusion, trehalose can modify the protein profile of ram spermatozoa during cryopreservation, which may be associated with its cryoprotective effects. Additionally, trehalose may function on frozen spermatozoa through antioxidation, involvement in glycolysis, and increment of spermatozoa tolerance to various stresses.

The Effects of Antifreeze Protein III Supplementation on the Cryosurvival of Goat Spermatozoa During Cryopreservation

Antifreeze protein (AFP) has been shown to have beneficial effects on frozen mammalian spermatozoa. However, rare reports have been published regarding the use of AFPs in storage of goat spermatozoa. The aim of this study was to investigate the effects of AFPIII on the quality of goat semen during cryopreservation. Ejaculates were collected from six Yunshang black goats through an artificial vagina. The collected semen was pooled, divided into five aliquots, and diluted with the commercial bull semen extender containing: no AFPIII (AFP-0, control), 1 μg/mL AFPIII (AFP-1), 10 μg/mL AFPIII (AFP-10), 50 μg/mL AFPIII (AFP-50), and 100 μg/mL AFPIII (AFP-100), respectively. Spermatozoa motility, membrane integrity, acrosome integrity, mitochondrial function, distribution of phosphatidylserine, and formation of reactive oxygen species (ROS) were measured after the freezing and thawing process. The results showed that the spermatozoa motility, membrane integrity, acrosome integrity, and mitochondrial function were significantly higher in frozen spermatozoa using the extender containing 1 μg/mL AFPIII as compared with the other groups (p < 0.05). Furthermore, the extender supplemented with 1 μg/mL of AFPIII resulted in higher viable and lower nonviable spermatozoa compared with the other treated groups (p < 0.05), after staining using Annexin V-fluoresceine isothiocyanate (Annexin V-FITC) and Propidium Iodide. No significant differences were found between these groups in relation to viable cells with lower ROS production. In conclusion, the addition of AFPIII to the freezing extender improved the post-thaw quality of goat semen. The optimal concentration used in this study was 1 μg/mL. However, excessively high concentrations of AFPIII were unable to exhibit their cryoprotective effects on goat spermatozoa. However, the presence of AFPIII cannot mitigate oxidative stress caused by the freezing and thawing process. In addition, in vitro fertilization or artificial insemination can further evaluate the effects of AFPIII on frozen-thawed goat spermatozoa.

Relationship between semen quality and seminal plasma cholesterol, triacylglycerols and proteins in the domestic cat

OBJECTIVES

The current study aimed to evaluate the relationship between specific seminal plasma components - cholesterol (CHOL), triacylglycerols (TAG) and total protein (PROT) concentrations - and semen quality in cats. A further aim was to determine the relationship between specific seminal protein bands and semen quality.

METHODS

Thirteen toms, 2-5 years of age, were included. Semen collection was performed by electroejaculation every 4 weeks. Fifty-eight ejaculates were assessed for motility, velocity, volume, sperm concentration, total sperm count, viability, acrosome integrity, plasma membrane integrity and sperm morphology. Samples were divided into two groups: good semen quality (GSQ) and poor semen quality (PSQ). After evaluation, seminal plasma was separated from the sperm by centrifugation and stored at -20°C. CHOL, TAG and PROT concentrations were then assessed and seminal plasma protein profile was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

Seminal plasma CHOL and TAG concentrations, motility, velocity, sperm concentration, total sperm count and sperm morphology were significantly higher in GSQ cats compared with PSQ cats (P <0.01). Moreover, seminal plasma SDS-PAGE analysis showed an identifiable extra band exclusively in the GSQ group.

CONCLUSIONS AND RELEVANCE

Data obtained in this study showed that seminal plasma CHOL and TAG concentrations and specific protein bands could be used to improve semen evaluation in toms. In this sense, the 14 kDa protein band could be a valuable marker for semen quality in the cat and should be further investigated. However, more studies are necessary to determine its relationship with fertility.

Effect of low-density lipoproteins and trehalose on the quality of cryopreserved bovine semen

Background: In artificial insemination, chicken egg yolk is added to bovine semen to protect it during the cryopreservation process, although it contains substances that can affect the microbiological quality and metabolism of sperm. Objective: To evaluate post-thaw quality of bovine cryopreserved semen added with centrifuged and non-centrifuged egg yolk, low-density lipoproteins (LDL), and trehalose (T). Methods: Ten ejaculates from five bulls were cryopreserved under the treatments T1: pure egg yolk (PEY) at 20% v/v, T2: centrifuged egg yolk (CEY) at 20% v/v, T3: LDL at 8% v/v, T4: T at 100 mM, and T5: T at 100 mM plus LDL at 8% v/v (TLDL). Spermatic motility and kinetics, functional membrane integrity (FMI), structural membrane integrity (SMI), sperm vitality (SV) and abnormal morphology (AM) were assessed using the Sperm Class Analyzer (SCA®) system, hypoosmotic test (HOST), SYBR/PI probes, and eosin–nigrosin staining, respectively. A completely randomized design was used. Normal distribution of the variables was validated through the Kolmogórov– Smirnov test. A generalized linear model was used to determine sources of variation. Means were compared using the Tukey test. Results: Inclusion of CEY or LDL had a similar effect on sperm protection, and were superior for motility, kinetics and membrane integrity compared to the other treatments (p<0.05). CEY was superior for progressive motility (p<0.05). The cryoprotective action of LDL was similar to TLDL for motility and kinetics, SMI, SV, and AM (p<0.05). Inclusion of PEY and T resulted in the lowest semen quality (p<0.05). The use of T resulted in a reduction in FMI and SMI (p<0.05). No differences in AM between treatments were found (p>0.05). Conclusions: Egg yolk can be replaced by centrifuged egg yolk or low-density lipoproteins in the freezing extender used for bovine semen used in artificial insemination.

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.

Sperm Cryodamage in Ruminants: Understanding the Molecular Changes Induced by the Cryopreservation Process to Optimize Sperm Quality

Sperm cryopreservation represents a powerful tool for livestock breeding. Several efforts have been made to improve the efficiency of sperm cryopreservation in different ruminant species. However, a significant amount of sperm still suffers considerable cryodamage, which may affect sperm quality and fertility. Recently, the use of different “omics” technologies in sperm cryobiology, especially proteomics studies, has led to a better understanding of the molecular modifications induced by sperm cryopreservation, facilitating the identification of different freezability biomarkers and certain proteins that can be added before cryopreservation to enhance sperm cryosurvival. This review provides an updated overview of the molecular mechanisms involved in sperm cryodamage, which are in part responsible for the structural, functional and fertility changes observed in frozen–thawed ruminant sperm. Moreover, the molecular basis of those factors that can affect the sperm freezing resilience of different ruminant species is also discussed as well as the molecular aspects of those novel strategies that have been developed to reduce sperm cryodamage, including new cryoprotectants, antioxidants, proteins, nanoparticles and vitrification.

Extenders modify the seminal plasma ability to minimize freeze-thaw damage on ram sperm

Seminal plasma (SP) proteins interact with sperm plasma membrane (PM) modulating its functionality. It has been shown that SP proteins can reverse the damage caused by freeze-thaw; however in these studies, SP has been added to washed sperm (i.e., cells depleted from homologous SP and extender). The aim of the current study was to assess whether the egg yolk-based extender (EY) modifies SP ability to ameliorate sperm parameters in frozen-thawed ram spermatozoa. Ejaculates were diluted in EY or soybean lecithin-based extender (SL) and evaluated before and after freezing to measure the cell damage according to the extender. Even when all classical parameters decreased after freezing, as expected (p < .05), there was no effect of the extender. SP treatment was applied after freeze-thaw. Sperm were incubated with SP (20% v/v) in the presence of either EY or SL, and sperm parameters were assessed after thawing compared with the same treatments after Percoll sperm selection (washed). Treatments with 20% SP improved sperm total and progressive motility compared with controls regardless of washing and extender (p < .05); however, washed sperm showed higher percentage of total sperm motility compared with those unwashed (p < .05). Moreover, treatment with 20% SP showed significantly higher percentages of PM integrity, sperm with intact acrosomes, integrity of chromatin and non-capacitated sperm in samples diluted with EY when washed before treatment compared with the other conditions (p < .05). It was concluded that the presence of the extenders and particularly egg yolk alters the SP capacity to reduce the cryodamage.

Recombinant peptide reverses cryo-capacitation in ram sperm and improves in vitro fertilization

Semen cryopreservation is a very important technique for assisted reproduction; however, the cryopreservation process is harmful because it results in a reduction in sperm motility and viability, and leads to premature signals of capacitation, resulting in lesser than desirable fertility rates after artificial insemination. A fraction of seminal plasma, enriched in proteins that contain type II fibronectin domains (FNII) can reverse molecular indicators of cryo-capacitation. The beneficial effects of these proteins, however, depend on the relative abundance in seminal plasma. To create a safe additive for improving frozen sperm functionality, in the present study there was cloning and expression of a recombinant peptide containing four FNII domains (named TrxA-FNIIx4-His6) and evaluation of its effect after addition to frozen/thawed ram sperm. The cDNA for this protein was expressed in E. coli and after denaturation and re-naturalization of the protein, toxicity and binding capacity were assessed. By fluorescent labelling assessment, there was binding of the protein to the thawed sperm. At the two doses used (0.15 and 0.3 μM), TrxA-FNIIx4-His6 had the capacity to reverse the molecular indicators of cryo-capacitation as indicated by the reduction on phosphorylated substrates of PKA. Furthermore, the supplementation with this protein resulted in a normal capacitation process as evidenced by the increase in the in vitro fertilization rate when the greatest concentration of the protein was evaluated (73.25 ± 2.95; 40.13 ± 11.82 for 0.3 μM and control, respectively). There was no effect of protein supplementation on sperm objective motility compared to untreated sperm. In conclusion, the use of TrxA-FNIIx4-His6 is a promising biotechnological approach for cryopreserving ram sperm and maintaining sperm viability.

Improving the quality of cryopreserved goat semen with a commercial bull extender supplemented with resveratrol

The purpose of the current study was to evaluate the effects of resveratrol (RSV) on the quality of frozen-thawed goat sperm. Semen samples from four bucks were divided into five aliquots and diluted with a commercial bull semen extender containing: no antioxidant (RSV-0, control), 10 μM RSV (RSV-10), 50 μM RSV (RSV-50), 100 μM RSV (RSV-100) and 250 μM RSV (RSV-250). After thawing, sperm motility, abnormal morphology, membrane and acrosome integrity, mitochondrial activity, phosphatidylserine (PS) distribution, and oxidative stress were evaluated. The results indicated that in comparison with the control, when the concentration of RSV was 10 or 50 μM, the total motility, progressive motility, membrane and acrosome integrity, and mitochondrial activity of post-thaw spermatozoa was greater (P < 0.05). Additionally, the use of extenders containing RSV-10 or RSV-50 resulted in a greater percentage of viable spermatozoa as compared to the other groups (P < 0.05). Importantly, there were more viable spermatozoa (49.61 ± 0.61%) and less non-viable spermatozoa (49.16 ± 1.01%) in the RSV-50 group compared to the other extenders (P < 0.05). Furthermore, the use of the extenders containing RSV-10 and -50 resulted in a reduction in ROS production in frozen-thawed spermatozoa as compared to the control (P < 0.05). There, however, was no difference among extenders for abnormal morphology and PS distribution. In conclusion, supplementation with RSV, at a concentration of 10 or 50 μM in the semen extender, can improve the post-thaw goat sperm quality, which may occur as a consequence of inhibition of ROS generation.

Potential of seminal plasma to improve the fertility of frozen-thawed boar spermatozoa

Artificial insemination (AI) is widely used for livestock breeding. Although sperm cryopreservation is the most efficient method for long-term storage, its use for porcine AI is marginal, because of its dramatic impact on sperm quality. While the removal of seminal plasma is a routine practice prior to porcine sperm cryopreservation, its beneficial role on sperm function has not been investigated in as much detail. In this context and despite seminal plasma being regarded as a mere vehicle of sperm, mounting evidence indicates that it could be positive for porcine sperm fertility. In effect, not only is seminal plasma able to interact with the female reproductive tract after mounting/insemination, but it has been demonstrated it modulates sperm function. For this reason, the composition of this fluid and its proteome have begun to be investigated in order to elucidate whether its components play any role in sperm function, fertility and cryotolerance. Previous research has demonstrated that seminal plasma may maintain the quality and fertilizing ability of frozen-thawed boar spermatozoa when added before or after cryopreservation. However, a large variety of results have been reported with both beneficial and detrimental effects, including studies in which no influence has been observed. This review examines the composition of porcine seminal plasma and summarizes the available published studies regarding seminal plasma supplementation to spermatozoa before or after freeze-thawing. The take-home message of this article is that clearing up the role of seminal plasma in sperm cryotolerance may increase the reproductive performance of frozen-thawed boar spermatozoa.

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.

Supplemented stallion seminal plasma can improve impaired motility due to the dilution effect in chilled Asian elephant sperm

The dilution effect and effect of restoring seminal plasma (SP) proportion in diluted semen were determined in chilled Asian elephant sperm. Semen was collected from eight males, and samples with ≥30% motile sperm were used in the study. Tris-glucose-egg yolk extender (TE) was used for cooled storage at 4°C for 48 hr. In experiment 1 (n = 18), semen was diluted to 1:1, 1:3, 1:7 and 1:15 with TE (volume per volume). There were no significant changes in sperm viability and sperm with normal acrosome integrity among dilutions, but sperm motility and motility velocities were greater (p < .05) in the 1:1 dilution than those of the 1:7 and 1:15 dilutions at 48 hr of storage. In experiment 2, supplemented SP was derived from elephants and stallions. In experiment 2.1, diluted semen (1:7 dilution) was restored with SP to obtain a 1:2 proportion (n = 8). Sperm motility, viability and sperm with normal acrosome integrity were similar among treatments, but motility velocities were greater (p < .05) with stallion SP at 48 hr of storage. In experiment 2.2, diluted semen (1:15 dilution) was restored with SP to obtain a 1:3 proportion (n = 10). Sperm viability and sperm with normal acrosome integrity were similar among treatments at 48 hr of storage. However, sperm motility and motility velocities were greater (p < .05) with stallion SP than those of others. In conclusion, elephant sperm motility was affected by a dilution effect and restoration of SP proportion with stallion SP, but not with elephant SP, could improve motility in chilled highly diluted sperm.

Seminal plasma proteins modify the distribution of sperm subpopulations in cryopreserved semen of rams with lesser fertility

Any physiological mechanism involved in sperm selection and semen improvement has effects on heterogeneous sperm populations. This is mainly due to the fact that sperm populations within a single ejaculate have considerable heterogeneity for many variables, such as motility which is meaningful in terms of understanding how some sperm cells possess fertility advantages as compared with other cells. In the present research, initially there was a multivariate and clustering analysis used to assess sperm motility data from cryopreserved ram semen to identify subpopulations and compare the distribution of these clusters between rams with lesser and greater fertility. There were four classifications made of sperm subpopulations (clusters): CL1 fast/linear/progressive sperm; CL2 fast/non-linear sperm; CL3 very fast/linear sperm with vigorous beating and CL4 slow/non-linear sperm. Rams with greater fertility had a lesser proportion of sperm considered as "hyperactivated" (CL2) and a greater proportion of slow and non-linear sperm (CL4) than sperm of rams with lesser fertility. In addition, the effects were assessed for the capacity of seminal plasma (SP) and interacting SP proteins (iSPP) that were present during different seasons of the year to improve the distribution of sperm within subpopulations of semen from rams with lesser fertility. The iSPP and SP were obtained by artificial vagina (AV) and electroejaculation (EE) during breeding and non-breeding seasons and added to thawed semen. All the aggregates had a significant effect on the distribution of sperm subpopulations and effects differed among seasons of the year and depending on collection method used. Even though, future studies are needed to assess the contribution of each subpopulation on ram sperm fertility, it is important that a multivariate analysis be used to evaluate the effect of a treatment on sperm quality variables.

Variation in seminal plasma alters the ability of ram spermatozoa to survive cryopreservation

Variation in the effect of seminal plasma on sperm function and fertility has been hypothesised to be due to differences between males and their seminal plasma composition. The freezing resilience of individual rams (n=17) was investigated to characterise inter-male variation. This was determined by measuring the degree of change in motility induced by cryopreservation (Experiment 1). Experiment 2 examined the effect of pooled seminal plasma from rams identified as having high or low resilience to freezing on the cryosurvival of washed spermatozoa from either high (n=3) or low (n=3) sperm freezing resilience rams. Immediately after thawing and throughout the incubation period (0-4h), spermatozoa from high-resilience rams frozen with high-resilience seminal plasma demonstrated superior motility to spermatozoa from high-resilience rams frozen with low-resilience seminal plasma (P<0.001). Similarly, spermatozoa from low-resilience rams frozen with high-resilience seminal plasma exhibited higher motility than spermatozoa from low-resilience rams frozen with low-resilience seminal plasma immediately after thawing (0h; P<0.001). The present study shows that variation in freezing resilience of ram spermatozoa is related to the source and composition of the seminal plasma.

Interaction of milk proteins and Binder of Sperm (BSP) proteins from boar, stallion and ram semen

BACKGROUND

Mammalian semen contains a family of closely related proteins known as Binder of SPerm (BSP proteins) that are added to sperm at ejaculation. BSP proteins extract lipids from the sperm membrane thereby extensively modifying its composition. These changes can ultimately be detrimental to sperm storage. We have demonstrated that bovine BSP proteins interact with major milk proteins and proposed that this interaction could be the basis of sperm protection by milk extenders. In the present study, we investigated if homologous BSP proteins present in boar, stallion and ram seminal plasma display a similar affinity for the milk proteins in order to assess whether the mechanism of sperm protection by milk for these species could be general.

METHODS

Skim milk was incubated with seminal plasma proteins (boar, stallion and ram), chromatographed on a Sepharose CL-4B column and protein fractions were analyzed by immunoblotting.

RESULTS

Boar, stallion and ram BSP proteins displayed affinity for a milk protein fraction (F1) mainly composed of α-lactalbumin, β-lactoglobulin, and κ-casein. They also had affinity for another milk protein fraction (F2) composed mostly of casein micelles. However, stallion BSP showed higher affinity for the fraction (F1).

CONCLUSIONS

These results further extend our view that the association of BSP proteins with milk proteins could be a general feature of the mechanism of mammalian sperm protection by milk to prevent detrimental effect of prolonged exposure of sperm to seminal plasma.

Seasonal changes in antioxidant defence systems in seminal plasma and fluids of the boar reproductive tract

This study aimed to analyze seasonal variations in the antioxidant defence systems of the seminal plasma and fluids of the cauda epididymis and vesicular glands of the boar. The analyzed antioxidants included superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and total L-glutathione (GSH+GSSG). Seasonal changes in total protein content and total antioxidant status (TAS) of the seminal plasma and reproductive fluids were also analyzed. Compared with the spring-summer period, total protein content in the seminal plasma was significantly higher during the autumn-winter period. Among the antioxidants analyzed, only SOD activity showed marked seasonal variations, being significantly higher during the spring-summer period. Likewise, the fluid of the cauda epididymis exhibited greater SOD and CAT activity during the spring-summer period, whereas TAS levels were markedly higher during the autumn-winter period. Neither GPx activity nor total GSH+GSSG content in the cauda epididymal fluid was significantly affected by the seasonal periods. The vesicular gland fluid exhibited an approximately 4-fold greater level of SOD activity during the autumn-winter period, as compared with the spring-summer period. By contrast, greater CAT and GPx activity, and a higher level of total GSH+GSSG were observed in the vesicular gland fluid during the spring-summer period. In conclusion, the findings of this study indicate that seasonal variations could have varying effects on the antioxidant defence systems in the seminal plasma and fluids of the boar reproductive tract.

WITHDRAWN: Major proteins from the seminal plasma of adult Santa Ines rams

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Seminal plasma proteins do not consistently improve fertility after cervical insemination of ewes with non-sorted or sex-sorted frozen - thawed ram spermatozoa

The effect of supplementation of sex-sorted and non-sorted spermatozoa with seminal plasma protein (SPP) on fertility after cervical insemination was examined in the present study. Spermatozoa were sorted into high purity X and Y chromosome-bearing spermatozoa or not sorted and then either supplemented with SPP (>10 kDa) before freezing and/or after thawing (non-sorted only) or processed without supplementation. Inseminations were performed over 2 days with ewes receiving 100 or 25 million motile non-sorted spermatozoa in the cervix or uterus, respectively, or two cervical inseminations of 3.5 million motile sorted spermatozoa. Pregnancy rates in cervically inseminated ewes were unaffected by supplementation of sorted or non-sorted spermatozoa with SPP before freezing compared with no supplementation. The effect of post-thaw supplementation of non-sorted spermatozoa with SPP on pregnancy rates after cervical insemination varied with the day of insemination (P < 0.05); fertility was similar to laparoscopic insemination on Day 1 (56.0 ± 10.2% v. 58.6 ± 10.1%), but not on Day 2 (23.1 ± 7.4% v. 66.7 ± 9.2%). In conclusion, under the conditions of the present study, SPP did not consistently improve pregnancy rates after cervical insemination with frozen–thawed ram spermatozoa. This is the first report of pregnancies (5/56 ewes inseminated) after cervical insemination with frozen–thawed sex-sorted ram spermatozoa. Although the success rate is low, the findings are encouraging because ewes inseminated with the sex-sorted spermatozoa received only 7% of the recommended dose (100 million motile) for cervical insemination of frozen–thawed spermatozoa.

Seasonal variation in the protective effect of seminal plasma on frozen-thawed ram spermatozoa

The response of ram spermatozoa to seminal plasma is highly variable, in part due to the presence of both stimulatory and inhibitory factors. The aim of this study was to assess variation in the protection of ram spermatozoa during freezing by seminal plasma. The seminal plasma variables studied were season of collection, fractionation and method of supplementation. Spermatozoa were supplemented before freezing with 4 mg of seminal plasma proteins (SPPs) per 10(8) cells, and their motility and viability were assessed during post-thaw incubation (37 degrees C). In Experiment 1, semen was (a) frozen with no supplementation (Control) (b) extended with a Tris-based diluent (C + TRIS), or (c) supplemented with seminal plasma collected throughout the year (in the Southern Hemisphere) and pooled for January-March, April-June, July-August and October-December, and either fractionated to produce a concentrated >10 kDa seminal plasma protein retentate (>10 kDa SPP), or kept as crude seminal plasma (CP). There was no effect of season or seminal plasma type (CP or >10 kDa SPP) on motility of spermatozoa. CP and >10 kDa SPP improved the viability of spermatozoa when collected from January-September compared to Control. Supplementation with >10 kDa SPP increased viability of spermatozoa, compared to CP, when collected from January to July. In Experiment 2, >10 kDa SPP were either added directly to the spermatozoa or included in the cryodiluent or >10 kDa SPP were not supplemented (Control). Both supplementation methods improved the motility and the proportion of viable, acrosome-intact spermatozoa but direct supplementation resulted in more viable, acrosome-intact spermatozoa compared with supplementation of the cryodiluent. These results show that supplementation of ram spermatozoa with CP, or its protein component (>10 kDa SPP), before freezing protects them from freeze-thaw damage. The protective effect is greatest when seminal plasma is collected during the breeding season, fractionated with >10 kDa filters and added directly to the spermatozoa.