An In Vitro Evaluation of Biochemical Processes Involved in Lead-Induced Changes on Ram Spermatozoa.

Lead (Pb(2+) ) is a toxic heavy metal which interferes with several physiological processes regulated by Ca(2+) , including those characterized by changes of the membrane stability and the motility of spermatozoa necessary for the fertilization of the oocyte. In this study, ejaculated sperm from six rams (Ovis aries) have been incubated in vitro with or without 50 ng Pb(2+) /ml during 30 min and in the presence or absence of three different potential modulators of the effects of Pb(2+) on changes in the sperm membrane before fertilization: charybdotoxin, quinacrine and staurosporine. Sperm samples incubated with Pb(2+) have shown significant reductions in acrosome integrity and sperm viability and an increase in progressive movement. None of the studied potential modulators had a protective effect against Pb(2+) action. On the contrary, Pb(2+) -incubated sperm in the presence of staurosporine had lower acrosome integrity, and lower sperm viability was observed when spermatozoa were incubated with Pb(2+) + charybdotoxin. Quinacrine was the only tested substance capable of increasing the concentration of Pb(2+) in spermatozoa; thus, the enhancement of Pb(2+) effects produced by staurosporine and charybdotoxin was not produced by an increased uptake of Pb(2+) by spermatozoa. However, the increase of intracellular Pb(2+) in those spermatozoa incubated with quinacrine did not result in an adverse effect on sperm motility or viability although the acrosome integrity was negatively affected.

Selection of red deer spermatozoa with different cryoresistance using density gradients.

The objective of sperm selection media is selecting the best spermatozoa and to remove seminal plasma and diluent for using them in assisted reproductive techniques. It is known that individuals show different cryoresistance in response to the same freezing procedure. Our hypothesis was that the efficacy of selection media could be dissimilar for samples with different sperm quality after thawing. Epididymal sperm samples from mature Iberian red deer were collected and frozen. Males were classified as with high post-thaw sperm quality when sperm motility (SM) ≥ 70%, or as with low post-thaw sperm quality when SM ≤ 69%. Samples were centrifuged using the following density gradients (DG): Percoll® , Puresperm® and Bovipure™ , and several functional sperm parameters were assessed after sperm selecting and washing. Males classified with high sperm quality had higher post-thawing values (p > .05) for all parameters evaluated, except for linearity index, than those categorized as low sperm quality. After selection, some sperm characteristics improved (viability, apoptosis and mitochondrial activity) for both groups, showing the males with high sperm quality higher values in all sperm parameters except for kinematic traits and DNA fragmentation index (%DFI), regardless of DG. Bovipure™ yield lower values of sperm motility, viability, apoptosis and mitochondrial activity in relation to Percoll® and Puresperm® considering both quality groups. There was an interaction between the type of DG and sperm quality group for sperm viability (p = .040) and apoptosis (p = .003). Thus, Percoll® selected less live and more apoptotic spermatozoa than Puresperm® and Bovipure™ for males with low sperm quality. In conclusion, the DG are more efficient selecting spermatozoa from samples with high sperm quality, acting differently depending on initial sperm quality.

Oestrous sheep serum balances ROS levels to supply in vitro capacitation of ram spermatozoa.

Reactive oxygen species (ROS) are fundamental for intracellular signalling. In spermatozoa, they are involved both to apoptosis and to capacitation, and changes in ROS levels can alter the balance between these two processes. Oestrous sheep serum (OSS) is considered an efficient agent for in vitro capacitation of ram spermatozoa. We have explored the effects of OSS on ram sperm physiology, especially on ROS production, during in vitro capacitation. Semen samples from 15 rams were cryopreserved. After thawing, samples were submitted to four treatments: control (CTL), 10% OSS supplementation for in vitro sperm capacitation, caspase inhibitor (INH, Z-VAD-FMK 100 µM) and OSS (10%) plus caspase inhibitor (I + E). Sperm samples were incubated for 30 min at 38.5°C and 5% CO2 and evaluated motility and kinetic parameters by computer-assisted semen analysis (CASA) and viability (propidium iodide), apoptotic-like membrane changes (YO-PRO-1), acrosomal status (PNA-FITC), intracellular calcium (FLUO-3), membrane fluidity (M540) and ROS production (CM-H2 DCFDA) by flow cytometry. OSS induced changes in kinetic parameters compatible with capacitation, with a decrease in the percentage of progressive motility and linearity, and an increase in the amplitude of the lateral displacement of the sperm head (p < .05). Moreover, OSS increased the proportion of M540+ viable spermatozoa, YO-PRO-1+ and acrosome-reacted spermatozoa (p < .05). After incubation, OSS and I+E achieved lower ROS levels (p < .05). Ca(2+) levels did not change with the incubation, but were slightly higher (p < .05) when both OSS and the inhibitor were present. We suggest that OSS may modulate ROS levels, allowing intracellular signalling for capacitation to occur while preventing higher levels that could trigger apoptosis.

The Effect of Oxidative Stress on Thawed Bulk-Sorted Red Deer Sperm.

The aims of this study were to assess the effects of the sex-sorting process on post-thaw sperm quality as well as on induced oxidative stress damage (H2 O2 0 mm = H000; H2 O2 50 mm = H050; H2 O2 100 mm = H100) and the protective action of reduced glutathione (GSH) and Trolox, when comparing sorted (BSS) and non-sorted (NS) red deer spermatozoa incubated at 37°C. Sperm samples from three stags were collected by electroejaculation and frozen. Immediately after thawing, sperm motility was higher (p < 0.05) for NS (59% ± 3.3) than BSS (36.9% ± 5.8) sperm. Furthermore, the percentage of apoptotic sperm was higher (p < 0.05) for BSS (21.6% ± 5.0) than NS sperm (14.6% ± 1.2). The presence of H2 O2 increased DNA damage in NS (H000 = 4.1% ± 0.9; H050 = 9.3% ± 0.7; and H100 = 10.9% ± 2.3), but not in BSS sperm. However, in the presence of oxidant, GSH addition improved (p < 0.05) sperm motility in both groups of sperm samples as compared to their controls (NS: 44.5 ± 4.8 vs 21.1 ± 3.9 and BSS: 33.3 ± 8.1 vs 8.9 ± 1.8). These results demonstrate that the sperm-sorting process induces sublethal effects, albeit selecting a sperm population with a chromatin more resistant to oxidative stress than that in non-sorted sperm. Moreover, addition of GSH at 1 mm may be a good choice for maintaining the quality of stressed sperm samples, unlike Trolox, which inhibited sperm motility.

Understanding sperm heterogeneity: biological and practical implications.

Sperm are the most diverse cell type known. This diversity is thought to reflect adaptation to conditions under which sperm function as a way to ensure the survival of sperm in fertilization environments and to maximize fertilizing capacity thereof. The existence of morphological diversity among species is widely assumed, although this diversity seems less clear as we go deeper (between males, between ejaculates from the same male and even within the same ejaculate), with different theories addressing this heterogeneity. Moreover, the development of assisted reproductive techniques (ART) has led to changes in the physiological conditions in which sperm fertilize, which could lead, ultimately, to a selection towards more favourable sperm design. Regardless of the origin of this diversity, when studying the relationship between shape and function of sperm, it is advisable to assess the degree of heterogeneity of sperm and takes into account to be more likely to identify those morphological characteristics determining the fertile ability of sperm. Otherwise, these relationships could be hidden as a result of considering an average shape not representative of morphological characteristics of sperm. In addition, the knowledge of this morphological diversity in terms of changes arising from modifications in the sperm environment and mechanisms that generate these changes could be useful for understanding the reproductive capacity of males but also in enhancing their fertile ability.

Response of thawed epididymal red deer spermatozoa to increasing concentrations of hydrogen peroxide, and importance of individual male variability.

Oxidative stress represents a challenge during sperm manipulation. We have tested the effect of increasing hydrogen peroxide (H(2)O(2)) levels on red deer spermatozoa after cryopreservation, and the role of male-to-male variation in that response. In a first experiment, eight thawed samples were submitted to 0, 25, 50, 100 and 200 µm H(2)O(2) for 2 h at 37 °C. Intracellular reactive oxygen species (H(2)DCFDA-CM) increased with H(2)O(2) concentration, but we only detected a decrease in sperm function (motility by CASA and chromatin damage by sperm chromatin structure assay) with 200 µm. Lipoperoxidation assessed by the thiobarbituric acid reactive substance (TBARS) method increased slightly with 50 µm H(2)O(2) and above. In a second experiment, samples from seven males were submitted to 0 and 200 µm H(2)O(2) for 2 h, triplicating the experiment within each male. Males differed at thawing and regarding their response to incubation and H(2)O(2) presence. We found that the kinematic parameters reflected male-to-male variability, whereas the response of the different males was similar for lipid peroxidation and viability. A multiparametric analysis showed that males grouped differently if samples were assessed after thawing, after incubation without H(2)O(2) or after incubation with H(2)O(2) . Red deer spermatozoa are relatively resilient to H(2)O(2) after thawing, but it seems to be a great male-to-male variability regarding the response to oxidative stress. The acknowledgement of this individual variability might improve the development of optimized sperm work protocols.

Cryopreservation of Iberian red deer (Cervus elaphus hispanicus) spermatozoa obtained by electroejaculation.

We tested extenders and freezing protocols for Iberian red deer semen. Samples were obtained by electroejaculation (10 stags), and analyzed for motility (CASA), viability (propidium ioide), acrosomal (PNA-FITC) and mitochondrial status (JC-1). Samples were diluted 1+1 in extender, cooled and adjusted for glycerol (extender with higher glycerol concentration), brought to 160 x 10(6)mL(-1) and frozen. Four experiments were carried out, repeating sperm analysis after thawing to compare treatments. In a first experiment, seven samples were frozen using Triladyl (20% egg yolk) and UL extender (Tes-Tris-fructose, 15% egg yolk, 4% glycerol). Triladyl yielded higher motility after thawing. In a second trial, 17 samples were frozen using Triladyl, Andromed, Bioxcell, and UL with 8% LDL (low-density lipoproteins). Triladyl, and Andromed performed better than Bioxcell on motility, and than UL-LDL on viability and acrosomal status. In a third experiment, the performance of freezing the sperm-rich ejaculate fraction versus the whole ejaculate was tested on nine samples. The sperm-rich ejaculate fraction not only rendered more motile and viable spermatozoa but also showed higher freezability (higher motile spermatozoa recovery). In a fourth experiment, we tried three modifications of the freezing protocol, for improving the freezability of low concentration samples: prior removal of seminal plasma; replacing extender (second fraction) for pure glycerol to reduce dilution; and performing only the 1+1 dilution, not the second dilution. No differences were found, although only three samples could be used. Both Triladyl and Andromed were deemed appropriate for freezing Iberian red deer semen, and the rich fraction should be selected for freezing.

Heterologous in vitro fertilization is a good procedure to assess the fertility of thawed ram spermatozoa.

A heterologous in vitro fertilization (IVF) test using calf oocytes with zona pellucida was employed to assess the fertility of thawed ram sperm samples. Six males with significant differences in fertility (P=0.003) were used. The males were classified as having high fertility (>or=42%) and low fertility (

Cinnamtannin B-1, a novel antioxidant for sperm in red deer.

Cinnamtannin B-1 (CNB-1) is a naturally occurring trimeric A-type proanthocyanidin contained in several plants such as cinnamon (Cinnamomum zeylanicum). It is considered to be a potent antioxidant. The protective effect of CNB-1 against oxidative stress was assessed in red deer epididymal sperm incubated at 37 °C. Cryopreserved sperm from six stags were thawed, pooled and extended to 400 × 106 sperm/ml in BGM (bovine gamete medium). After being aliquoted, the samples were supplemented with different concentrations of CNB-1 (0, 0.1, 1, 10 and 100 µg/mL), with or without induced oxidative stress (100 µM Fe2+/ascorbate). The samples were evaluated after 0, 2 and 4 h of incubation at 37 °C. This experiment was replicated six times. Spermmotility (CASA), viability, mitochondrial membrane potential, acrosomal status, lipoperoxidation (C11 BODIPY 581/591), intracellular reactive oxygen species (ROS) production and DNA status (TUNEL) were assessed. After 4 h of incubation, CNB-1 prevented the deleterious effects of oxidative stress, thus improved sperm progressivity and velocity (P<0.05). Furthermore, 1 and 10 µM CNB-1 improved sperm linearity, even when compared to those samples that had not been subjected to oxidative stress (P<0.05). The greatest concentration, 100 µM, prevented sperm lipoperoxidation and reduced ROS production in samples subjected to oxidative stress.

Effect of sex-sorting and cryopreservation on the post-thaw sperm quality of Iberian red deer spermatozoa.

This study investigated the effect of sex-sorting and cryopreservation on post-thaw characteristics and fertility of red deer (Cervus elaphus) sperm for the first time. Semen was collected by electroejaculation from 10 mature stags during the breeding season, and each ejaculate split into four experimental groups: Bulk sorted spermatozoa, sorted but not sexed (BSS); sorted high purity X-spermatozoa (XSS); sorted high purity Y-spermatozoa (YSS); and, control non-sorted spermatozoa (NS). Following, all samples were frozen over liquid nitrogen. Two straws per stag and sample type were analyzed immediately post-thaw and following a 2-h incubation period at 37 °C. Post-thaw total motility (TM) as assessed by CASA was not different (P < 0.05) among NS, BSS and YSS sperm. For XSS, post-thaw TM was lower (39%, P < 0.05) than that for NS (54%) or BSS (50%), but similar (P > 0.05) to that of YSS (47%) sperm. The percentage of apoptotic spermatozoa as assessed by PI/YO-PRO-1 and flow cytometry analysis, was higher (17%, P ≤ 0.05) for XSS sperm than NS (12%), BSS (13%) and YSS (14%) sperm. Following incubation there were no differences (P > 0.05) in TM or percent apoptosis among treatments. Post-thaw chromatin stability calculated as the DNA fragmentation index (%DFI) was similar among treatments; following incubation %DFI increased in all except YSS, which displayed the lowest value (P < 0.05). Artificial insemination of synchronized hinds yielded 44, 52 and 62% delivery rates for YSS, NS and standard frozen-thawed sperm, respectively (P < 0.05). Notably, 93 and 55% of fawns born were males for the YSS and NS spermatozoa, respectively (P < 0.05). In summary, Y-sorted sperm displayed acceptable post-thaw sperm evaluation parameters and the expected offspring sex ratio. More studies are needed to understand the source of sperm damage that may compromise the fertility of Y-sorted red deer sperm.

Estrous sheep serum enables in vitro capacitation of ram spermatozoa while preventing caspase activation.

Estrous sheep serum (ESS) is considered the most efficient agent for in vitro capacitation of ram spermatozoa. We have explored the relationship between caspase activation and capacitation in ram. Semen samples from 17 rams were cryopreserved. In vivo fertility was evaluated after intrauterine artificial insemination. Samples were submitted to four treatments: control, ESS (10%), caspase inhibitor (Z-VAD-FMK), and estrous ewe serum plus caspase inhibitor (I + E). Sperm samples were incubated for 30 minutes at 38.5 °C and 5% CO2 and analyzed with flow cytometry for mitochondrial membrane potential (MitoTracker deep red), sperm viability and apoptosis-like changes (YO-PRO-1/propidium iodide), acrosomal status (peanut agglutinin-fluorescein isothiocyanate), membrane fluidity (merocyanine 540), and caspase activity (Vybrant FAM kits for polycaspases, caspase-8, and caspases 3-7). Estrous sheep serum induced changes compatible with capacitation, doubling the proportion of viable spermatozoa with increased merocyanine 540 and increasing YO-PRO-1(+) and acrosome-reacted spermatozoa (P < 0.05). Incubation increased the proportion of spermatozoa with activated caspases (P < 0.05), which was abolished by the treatments. We detected a simultaneous decrease in the proportion of the viable and caspase(-) spermatozoa after the incubation, which was prevented by the presence of estrous ewe serum (P < 0.05). The analysis of caspases 3/7 and 8 resulted in less marked differences. Fertility was positively related to viability and inactivated caspases and negatively to viable-capacitated spermatozoa and active caspases. In vitro induction of capacitation in thawed ram spermatozoa by using ESS suggests a downregulation in apoptotic pathways. However, males with the lowest fertility showed parameters similar to high-fertility males, suggesting that other factors were involved apart from capacitation and/or caspase activation.

Influence of semen collection method on sperm cryoresistance in small ruminants.

Semen collection for cryopreservation is a key step for small ruminant conservation programs. While in these species semen is mainly collected via artificial vagina (AV), electroejaculation (EE) provides a viable alternative for untrained males. Herein we investigated the effect of semen collection method on post-thaw sperm quality by comparing two small ruminant species, sheep and goats. Semen from Blanca-Celtibérica bucks and Manchega rams was collected by AV and EE on the same day and cryopreserved using a standard protocol. At thawing, sperm motion parameters were evaluated by CASA, whereas membrane stability (YO-PRO-1), sperm viability (propidium iodide, PI) and mitochondrial activity (Mitotracker Deep Red) were analyzed using flow cytometry. The semen collection method negatively affected post-thaw sperm quality in bucks but not in rams. Thus, in bucks, post-thaw sperm motility was higher for samples collected by AV as compared to those obtained via EE. Similarly, post-thaw sperm parameters evaluated by flow cytometry were worse for buck samples collected by EE than those collected by AV in the same species, or than ram samples regardless of collection method. These results suggest that ovine and caprine spermatozoa have a different response to the cryopreservation process depending upon the semen collection method used. We hypothesize that the EE procedure may lead to changes in the composition of the ejaculate in bucks that would make spermatozoa more susceptible to the cryopreservation process, whereas this procedure would have had no effect on ram spermatozoa. This assumption requires further investigation.

Reduced glutathione addition improves both the kinematics and physiological quality of post-thawed red deer sperm.

The potential protective effect of reduced glutathione (GSH) and trolox (TRX), an analogue of vitamin E, supplementation during in vitro culture (2h, 39°C) of electroejaculated frozen/thawed red deer sperm was investigated. Cryopreserved sperm were thawed and incubated with no additive (Control) and 1mM or 5mM of each antioxidant to find out whether these supplementations can maintain the sperm quality, considering the use of thawed samples for in vitro techniques such as in vitro fertilisation (IVF), sperm sex sorting or refreezing. The effect of GSH on sperm motility was positive compared to TRX which was negative (P<0.001). After 2h of incubation at 39°C, use of GSH improved motility while TRX supplementation reduced sperm motility compared with Control samples without antioxidant. Use of TRX at both concentrations (1 and 5mM; TRX1 and TRX5) resulted in lesser percentages of apoptotic sperm (12.4±1.1% and 11.7±0.9%) than GSH1, GSH5 (15.2±1% and 14.6±1.1%) and Control samples (16.9±1.2%) (P<0.001). Use of GSH at both concentrations (1 and 5mM) resulted in greater mitochondrial activity as compared with findings for the Control, TRX1 and TRX5 groups. Results of this study indicate that GSH is a suitable supplement for electroejaculated red deer sperm. It would be necessary to conduct fertility trials (in vivo and in vitro), to assess whether GSH supplementation of thawed red deer sperm could improve fertility rates.

Sperm head phenotype and male fertility in ram semen.

Although there is ample evidence for the effects of sperm head shape on sperm function, its impact on fertility has not been explored in detail at the intraspecific level in mammals. Here, we assess the relationship between sperm head shape and male fertility in a large-scale study in Manchega sheep (Ovis aries), which have not undergone any selection for fertility. Semen was collected from 83 mature rams, and before insemination, head shapes were measured for five parameters: area, perimeter, length, width, and p2a (perimeter(2)/2×π×area) using a computer-assisted sperm morphometric analysis. In addition, a cluster analysis using sperm head length and p2a factor was performed to determine sperm subpopulations (SPs) structure. Our results show the existence of four sperm SPs, which present different sperm head phenotype: SP1 (large and round), SP2 (short and elongated), SP3 (shortest and round), and SP4 (large and the most elongated). No relationships were found between males' fertility rates and average values of sperm head dimensions. However, differences in fertility rates between rams were strongly associated to the proportion of spermatozoa in an ejaculate SP with short and elongated heads (P < 0.001). These findings show how the heterogeneity in sperm head shape of the ejaculate has an effect on reproductive success, and highlight the important role of modulation of the ejaculate at the intraspecific level.

Effect of different media additives on capacitation of frozen-thawed ram spermatozoa as a potential replacement for estrous sheep serum.

Capacitation is a key process through which spermatozoa acquire their fertilizing ability. This event is required for the successful application of assisted reproductive technologies such as IVF. The aim of the present study was to investigate the effect of using a synthetic oviductal fluid medium supplemented with either heparin-hypotaurine alone, in combination with progesterone (P4), 17ß-estradiol (E2), or BSA, or just ß-cyclodextrin, in replacement for estrous sheep serum (ESS) for ram sperm capacitation. After incubation in the corresponding media for 15 (time 0) or 60 minutes, sperm function was evaluated by computerized sperm motility analysis and flow cytometry (plasma membrane status and fluidity). Treatments rendering the best results in regards to sperm function parameters related to capacitation were used for an IVF test. Herein, neither heparin-hypotaurine (alone), or in combination with P4, or E2, nor ß-cyclodextrin induced capacitation-related changes in frozen-thawed ram spermatozoa. Only the medium supplemented with heparin-hypotaurine-BSA was able to induce changes compatible with in vitro capacitation relating to sperm motility pattern and plasma membrane fluidity, comparable to those in ESS-containing medium. Both media yielded sperm parameter values that differed (P < 0.05) from those obtained in the rest of the media tested. However, after the IVF trial, BSA was unable to support cleavage rates (21.80%) comparable to those obtained with ESS (52.60%; P < 0.05). We conclude that heparin-hypotaurine, P4, E2, ß-cyclodextrin, or BSA is not suitable for replacing ESS in capacitation and fertilization media for ram spermatozoa.

Fertility of cryopreserved ovine semen is determined by sperm velocity.

The present study aims to examine the predictive value of some sperm parameters on male fertility. Semen samples from six Manchega rams were collected and cryopreserved. Sperm quality was assessed after thawing and after 2h of incubation, either in the freezing extender (37°C) or after dilution in Synthetic Oviductal Fluid (SOF) (38°C, 5% CO2), attempting to mimic the physiological conditions of the female reproductive tract. The following sperm parameters were evaluated: motility and kinetic parameters by computer-assisted semen analyzer (CASA), and sperm viability (propidium iodide), mitochondrial membrane potential (JC-1), apoptotic-like membrane changes (YO-PRO-1), acrosomal status (PNA-FITC), and intracellular calcium (fluo-3) by flow cytometry. Results showed no significant differences between incubation media neither after thawing nor after incubation. There were no significant correlations between fertility and sperm parameters assessed by flow cytometry. However, after incubation in the freezing extender, sperm samples from males with poor fertility yielded less linearity and velocity (P<0.05) as indicated by motility parameters analyzed by CASA. These results indicate that kinematic sperm motility parameters evaluation by CASA might be useful to identify samples with poor fertility.

Morphometrically-distinct sperm subpopulations defined by a multistep statistical procedure in ram ejaculates: intra- and interindividual variation.

The existence of sperm subpopulations within the mammalian ejaculate has now been widely recognized. However, to the best of our knowledge, no data exist regarding the existence of sperm morphometric subpopulations within the ovine ejaculate. Computer assisted sperm morphometry analysis (ASMA) data and clustering methods were used in this study to identify sperm-head subpopulations in ram semen. Two experiments were carried out. In Experiment 1, ejaculates from 226 mature rams of the Manchega breed belonging to 36 different herds were used. A minimum of 100 sperm heads were analyzed from each male and eight morphometric characteristics for each individual sperm were recorded. Subpopulation analysis was performed in sequential steps: variable group analysis and correlation analysis to select which morphometric characteristics to use in cluster analyses; nonhierarchical clustering analysis using sperm head length and p2a (also known as roundness) shape factor as initial classificatory variables; and hierarchical clustering analysis to obtain the final number of clusters. The clustering analyses, based on 26,306 individual cells, revealed the existence of four sperm subpopulations (SP1, SP2, SP3 and SP4) with different morphometric characteristics. Significant differences in the proportion of spermatozoa in the SP1 and SP3 were found between rams belonging to different herds. In Experiment 2, the intra- and intermale variability on the distribution of sperm subpopulations was assessed. Three ejaculates from each of 21 rams were collected and the same multistep clustering analysis was performed. For all subpopulations defined, the intermale variability resulted in high values, being the intramale variability much lower. This fact would allow the use of sperm head morphometry to characterize a male and might provide valuable information to asses its fertility. In conclusion, our results show that using computer assisted sperm morphometry analysis and multivariate cluster analyses, four sperm subpopulations with different head phenotype were identified in ram ejaculates.

Taking advantage of the use of supervised learning methods for characterization of sperm population structure related with freezability in the Iberian red deer.

Using Iberian red deer as a model, this study presents a supervised learning method, the Support Vector Machines (SVM), to characterize sperm population structure related with freezability. Male freezability was assessed by evaluating motility, membrane status and mitochondrial membrane potential of sperm after a freezing-thawing procedure. The SVM model was generated using sperm motility information captured by computer-assisted sperm analysis (CASA) from thawed semen, belonging to six stags with marked differences on their freezability. A total of 1369 sperm tracks were recorded for seven kinematic parameters and assigned to four motility patterns based on them: weak motile, progressive, transitional and hyperactivated-like. Then, these data were split in two sets: the training set, used to train the SVM model, and the testing set, used to examine how the SVM method and three other unsupervised methods, a non-hierarchical, a hierarchical and a multistep clustering procedures, performed the sperm classification into subpopulations. The SVM was revealed as the most accurate method in the characterization of sperm subpopulations, showing all the sperm subpopulations obtained in this way high significant correlations with those sperm parameters used to characterize freezability of males. Given its superiority, the SVM method was used to characterize the sperm motile subpopulations in Iberian red deer. Sperm motile data from frozen-thawed semen belonging to 25 stags were recorded and loaded into the SVM model. The sperm population structure revealed that those males showing poor freezability were characterized by high percentages of sperm with a weak motility pattern. In opposite, males showing good freezability were characterized by higher percentages of sperm with a progressive and hyperactivated-like motility pattern and lower percentages of sperm with a weak motile pattern. We also identified a sperm subpopulation with a transitional motility pattern. This subpopulation increased as the freezability of males improved, and may be used as indicative of overall sperm motility.

Single layer centrifugation (SLC) improves sperm quality of cryopreserved Blanca-Celtibérica buck semen.

The aim of the present study was to evaluate the effect of sperm selection by means of single layer centrifugation (SLC) on sperm quality after cryopreservation, either when SLC is used before freezing or after thawing, using Blanca-Celtibérica buck semen collected by electroejaculation (EE). Ejaculates from six bucks were collected by EE and divided into two aliquots. One of them (unselected) was diluted with Biladyl(®) by the two-step method and frozen over nitrogen vapor. The other aliquot was selected by the SLC technique and subsequently frozen in the same way as the unselected samples (SLC before freezing). In a further treatment, two unselected straws were thawed and SLC was carried out (SLC after thawing). At thawing, sperm motility of all samples ((i) unselected; (ii) selected before freezing and (iii) selected after thawing) was evaluated by CASA. In addition, integrity of the plasma membrane, mitochondrial membrane potential, ROS production and DNA fragmentation index were assessed by flow cytometry. Most of the sperm parameters were improved (P≤0.001) in samples selected by SLC after thawing in relation to unselected or selected by SLC before freezing. The percentage of progressive motile spermatozoa was greater (86%) for sperm samples selected after thawing compared with unselected (58%) or selected before freezing (54%). Moreover, percentages of spermatozoa with intact plasma membrane and spermatozoa with high mitochondrial membrane potential (hMMP) were also greater for sperm samples selected after thawing compared to sperm samples unselected or selected before freezing (spermatozoa with intact plasma membrane: 80% vs. 32% vs. 12%; spermatozoa with hMMP: 54% vs. 1% vs. 15%; respectively). Therefore, sperm quality after cryopreservation is improved in Blanca-Celtibérica buck ejaculates collected by EE when a sperm selection technique such as SLC is carried out after thawing.

Effect of semen collection method (artificial vagina vs. electroejaculation), extender and centrifugation on post-thaw sperm quality of Blanca-Celtibérica buck ejaculates.

The aim of this study was to evaluate the effect of semen collection method (artificial vagina compared to electroejaculation), season in which the semen was collected (breeding season compared to non-breeding season), freezing extender (Biladyl(®), Andromed(®) and skim milk based extender) and pre-treatment procedure (washing compared to non-washing) on post-thaw semen quality in buck. Ejaculates from seven bucks of the Blanca-Celtibérica breed were collected by artificial vagina and electroejaculation during the breeding (July to December) and non-breeding season (January to June). Samples were split in two aliquots and one of them was washed. Three freezing extenders were evaluated on washing and non-washing sperm samples. Ejaculates collected by artificial vagina had a greater sperm quality after thawing, with greater values (P≤0.05) for SM (sperm motility), NAR (acrosome intact), YO-PRO-1-/PI- (intact spermatozoa), and Mitotracker+/YO-PRO-1- (spermatozoa with active mitochondria) and lower % DFI (DNA fragmentation index). Thawed sperm samples which were collected during the breeding season had greater values (P≤0.05) for NAR, intact spermatozoa and spermatozoa with active mitochondria, than those semen samples obtained during the non-breeding season. Semen freezing with Biladyl(®) and Andromed(®) resulted in a greater sperm quality (P≤0.05) after thawing in relation to milk-based extender. Washing procedure had no effect on sperm parameters assessed at thawing. Results from the present study suggest that the success of semen cryopreservation in Blanca-Celtibérica goat depends on semen collection method and season, as well as on the extender used. Thus, the post-thaw sperm quality will be greater (P≤0.05) when samples are collected by artificial vagina during the breeding season and when Biladyl(®) or Andromed(®) are used as freezing extenders.