Interrelationships among fluorometric analyses of spermatozoal function, classical semen quality parameters and the fertility of frozen-thawed bovine spermatozoa

Factors affecting the success of laparoscopic artificial insemination in sheep

Successful artificial breeding underpins rapid genetic and production gains in animal agriculture. In sheep, artificial insemination with frozen semen is performed via intrauterine laparoscopy as frozen-thawed spermatozoa do not traverse the cervix in sufficient numbers for high fertility and transcervical insemination is anatomically impossible in most ewes. Historically, laparoscopic artificial insemination has always been considered reasonably successful, but recent anecdotal reports of poor fertility place it at risk of warning adoption. Understanding the male, female and environmental factors that influence the fertility of sheep is warranted if the success of artificial insemination is to be improved and genetic progress maximised for the sheep industry. This review details the current practice of laparoscopic AI in sheep. It explores the effects of semen quantity and quality, the ewe, her preparation, and environmental conditions, on the fertility obtained following laparoscopic artificial insemination.

Evaluation of boar and bull sperm capacitation and the acrosome reaction using flow cytometry

Flow cytometry can be used to evaluate many sperm attributes and Dr. Duane Garner was influential in developing assays to understand sperm physiology and function. We review some of Dr. Garner's work and describe experiments that evaluate sperm capacitation using Dr. Garner's philosophy. In exploratory experiments, boar sperm were cryopreserved in lactose egg yolk (LEY) or Beltsville Freezing Extender 5 (BF5) and incubated in one capacitating medium. In another experiment, frozen-thawed bull sperm were incubated in TALP-Ca or CFDM1 capacitating media. In both experiments, sperm viability and capacitation were evaluated using multiple probes. Boar sperm frozen in LEY had greater survival rates (38%) than sperm frozen in BF5 (22%; P < 0.05) but did not capacitate as effectively as sperm in BF5 (P < 0.05). In Experiment 2, bull sperm survived to a greater extent when incubated in TALP-Ca than in CFDM1 (P < 0.05) and had greater capacitation for most parameters (P < 0.05). Of particular interest, 77% of sperm incubated in TALP-Ca had activated second messenger systems involved in capacitation, compared with < 5% of sperm incubated in CFDM1. The results indicate different freezing and capacitating media induce different responses to sperm capacitation and functions. If only sperm viability and acrosomal integrity were evaluated, these results would be interpreted very differently. Dr. Garner's philosophy of evaluating multiple sperm parameters was an impetus to determine unique treatment differences which help in understanding sperm capacitation, and design further experiments to determine how media content causes sperm physiology differences.

RhoA improves cryopreservation of rooster sperm through the Rho/RhoA-associated Kinase/cofilin pathway

Cryopreservation of rooster sperm leads to relatively low semen quality due to cytoskeletal damage during the freeze-thawing process. This study aimed to explore how the addition of RhoA recombinant protein affected the viability and subcellular structure of rooster sperm after freeze-thawing and elucidated the molecular mechanisms of sperm cryopreservation. Semen quality and acrosome integrity testing revealed that the addition of 0.5 μg/mL RhoA recombinant protein to the cryoprotectant fluid significantly increased sperm motility, survival rate, linearity, straight-line velocity, and acrosome integrity after freeze-thawing (P < 0.05). Ultrastructure analysis of cryopreserved sperm showed structural damage to the sperm plasma membrane, nuclear membrane, and tail. However, compared to the control, these structural changes were reduced upon the addition of RhoA recombinant protein to the cryoprotective fluid (P < 0.05). Western blotting revealed that the expression of Rho/RhoA-associated kinase and p-cofilin was increased, and cofilin expression was decreased after sperm cryopreservation with recombinant RhoA protein. Treatment with Y-27632, a ROCK antagonist, suppressed ROCK and p-cofilin expression and decreased semen quality, acrosome integrity, and ultrastructure integrity. In summary, we have demonstrated a cryoprotective effect in spermatozoa involving the Rho/ROCK pathway during freeze-thawing. Furthermore, the addition of 0.5 μg/mL RhoA recombinant protein to the cryoprotective fluid improved rooster semen quality and subcellular structural homeostasis after freeze-thawing via the Rho/ROCK pathway. This pathway may regulate the dynamic reorganization of the actin cytoskeleton by regulating the cofilin phosphorylation.

Proteomic comparison of non-sexed and sexed (X-bearing) cryopreserved bull semen

It is widely recognized that quality of spermatozoa in sexed semen (SS) samples is not as great as for conventional, non-sexed semen (NS). There are differences in qualitative and biochemical variables between spermatozoa in NS and SS. Information, however, is lacking on molecular differences, especially concerning spermatozoa proteomic differences is SS and NS. The objective of this study was to compare commercially available NS and SS bull semen by evaluating sperm quality variables in conjunction with a proteomics approach. Results from flow cytometry and computer-assisted sperm analyses indicated there was less sperm motility, viability, mitochondrial potential and acrosome integrity in sperm from SS. Results from proteomic analysis indicated sperm from NS and SS samples were characterized by different protein profiles. There was identification of 70 sperm proteins that differed in abundance and six protein spots that were different in extent of carbonylation. Sperm from SS had altered structures of enzymes involved in glycolysis, oxidative phosphorylation and maintenance of a constant adenylate energy charge. Furthermore, sperm from SS had alterations of several flagella substructures, especially outer dense fiber proteins, which were less abundant and more carbonylated than in sperm from NS. In sperm of SS, compared with NS, there were differences in abundance of proteins involved in capacitation, acrosome reaction and sperm-egg fusion as well as lesser abundances of sperm surface proteins. Results enable a greater understanding of differences between sperm from NS and SS samples, thereby contributing to development of improved protocols for more effective protection of sexed spermatozoa during processing.

Effects of single layer centrifugation (SLC) on bull spermatozoa prior to freezing on post-thaw semen characteristics

Single layer centrifugation (SLC) has been shown to select the most robust spermatozoa from the ejaculate in several species. Here the effects of SLC prior to freezing on various parameters of frozen-thawed bovine sperm quality are reported. Semen from 8 bulls was layered on top of a species-specific colloid, Bovicoll. After centrifugation for 20 min at 300 g, the resulting sperm pellet was resuspended in OPTIXcell^® (IMV Technologies, l'Aigle, France); the SLC-selected sperm samples and uncentrifuged controls were frozen. On thawing, all sperm samples were analysed for membrane integrity, production of reactive oxygen species, mitochondrial membrane potential (MMP) and chromatin integrity. The SLC-treated samples had a higher percentage of live, superoxide-positive spermatozoa than uncentrifuged samples (27.9 ± 5.1% versus 21.7 ± 6.7%; p = .03). They had a higher proportion of spermatozoa with high mitochondrial membrane potential than uncentrifuged samples (55.9 ± 8.2% versus 40.5 ± 15.1%; p = .03) and also a lower proportion of spermatozoa with low mitochondrial membrane potential than non-treated samples (42.0 ± 8.5% versus 55.9 ± 14.4%; p = .04). No significant effects of treatment were found for membrane integrity or chromatin integrity. The effect of bull was significant on the proportions of dead, superoxide-positive spermatozoa and live, hydrogen peroxide-negative spermatozoa, as well as on membrane integrity, but it was not significant for mitochondrial membrane potential or chromatin integrity. These results suggest that SLC selects the most metabolically active bull spermatozoa from the rest of the population in normal ejaculates; the pattern of reactive oxygen species production may be different in SLC-selected spermatozoa compared to unselected samples.

Effects of various physical stress factors on mitochondrial function and reactive oxygen species in rat spermatozoa

The aim of the present study was to evaluate the effects of various physical interventions on the function of epididymal rat spermatozoa and determine whether there are correlations among these functional parameters. Epididymal rat spermatozoa were subjected to various mechanical (pipetting, centrifugation and Percoll gradient separation) and anisotonic conditions, and sperm motility, plasma membrane integrity (PMI), mitochondrial membrane potential (MMP) and intracellular reactive oxygen species (ROS) were evaluated. Repeated pipetting caused a loss in motility, PMI and MMP (P<0.05). Minimal centrifugation force (200 g) had no effect on motility, PMI and MMP, whereas an increase in the centrifugation force to 400 g or 600 g decreased sperm function (P<0.005). Percoll gradient separation increased total motility, PMI and MMP (P<0.05). However, the spermatozoa that were subjected to mechanical interventions showed high susceptibility to a ROS stimulant (P<0.005). Anisotonic conditions decreased motility, PMI and MMP, and hypotonic conditions in particular increased basal ROS (P<0.05). In correlation tests, there were strong positive correlations among total motility, PMI and MMP, whereas ROS showed no or negatively weak correlations with the other parameters. In conclusion, the physical interventions may act as important variables, affecting functional parameters of epididymal rat spermatozoa. Therefore, careful consideration and proper protocols for handling of rat spermatozoa and osmotic conditions are required to achieve reliable results and minimise damage.

Effects of two homeopathic complexes on bovine sperm mitochondrial activity

OBJECTIVES

This study was conducted to evaluate the effect of two homeopathic complexes Ubichinon compositum® (Ubi comp) and Coenzyme compositum ad us. vet.® (CoQ10 comp) on bovine sperm mitochondrial activity.

METHODS

Sperm viability, acrosomal integrity and sperm chromatin structure were estimated to detect the possible side effect of complexes on other sperm parameters.

RESULTS

Mitochondrial activity was significantly enhanced by both Ubi comp (P<0.01) and CoQ10 comp (P<0.05). No effects were detected in other tested sperm parameters.

CONCLUSION

The tested homeopathic complex medicines stimulate the mitochondrial activity of bovine sperm without effects on their viability, acrosomal integrity or chromatin structure. The possibility that this translates into improved fertilization capacity in artificial insemination should investigated.

Integration of Sperm Motility and Chemotaxis Screening with a Microchannel-Based Device

BACKGROUND

Sperm screening is an essential step in in vitro fertilization (IVF) procedures. The swim-up method, an assay for sperm motility, is used clinically to select the ideal sperm for subsequent manipulation. However, additional parameters, including acrosome reaction capability, chemotaxis, and thermotaxis, are also important indicators of mammalian sperm health. To monitor both sperm motility and chemotaxis simultaneously during sperm screening, we designed and constructed a microdevice comprising a straight channel connected with a bibranch channel that mimics the mammalian female reproductive tract.

METHODS

The width and length of the straight channel were optimized to select the motile sperms. We selectively cultured cumulus cells in the bibranch channel to generate a chemoattractant-forming chemical gradient. Sperm chemotaxis was represented by the ratio of the sperm swimming toward different branches.

RESULTS

The percentage of motile sperms improved from 58.5% (3.8%) to 82.6% (2.9%) by a straight channel 7 mm in length and 1 mm in width. About 10% of sperms were found to be chemotactically responsive in our experiment, which is consistent with previous studies.

CONCLUSIONS

For the first time, we achieved the combined evaluation of both sperm motility and chemotaxis. The motile and chemotactically responsive sperms can easily be enriched on a lab-on-a-chip device to improve IVF outcome.

Effects of nonylphenol on motility and subcellular elements of epididymal rat sperm

Nonylphenol (NP) is an important environmental toxicant and potential endocrine disrupting chemical. The objective of these studies was to determine the effects of NP on epididymal rat sperm in vitro. Epididymal sperm samples from Sprague-Dawley rats were incubated in 1, 10, 100, 250, and 500 microg/ml NP for 1, 2, 3, or 4h. Computer-assisted sperm analysis was used to determine motility. Epifluorescent microscopy was used to determine acrosomal status and flow cytometry was used to determine mitochondrial membrane potential (MMP) and chromatin integrity. Exposure of epididymal rat sperm to 250 or 500 microg/ml NP was highly detrimental to motility (P<0.05), with complete loss of motility observed after exposure to 500 microg/ml NP (P<0.05). The acrosomal integrity of sperm was significantly reduced with the lowest concentration (1 microg/ml) of NP, and higher concentrations resulted in a dose-dependent induction of the acrosomal reaction (P<0.05). Similarly, the percentage of sperm with high MMP declined dramatically after exposure to 100, 250, and 500 microg/ml NP (P<0.05). Duration of NP exposure did not have any effect on motility or MMP and NP did not appear to have detrimental effects on chromatin integrity (P>0.05). These results indicate that major mechanism of action of NP on rat sperm is by adversely affecting their acrosomal integrity. However, NP-induced impaired sperm motility, decreased mitochondrial membrane potential also likely to play an important role in destruction of sperm function.

Seasonal variation in nuclear DNA integrity of frozen-thawed spermatozoa from Thai AI swamp buffaloes (Bubalus bubalis)

In this study, we investigated the susceptibility of frozen-thawed swamp buffalo sperm nuclear DNA to undergo controlled acid-induced denaturation in situ, as analysed by flow cytometry, and aimed to correlate the results with sperm head morphology over three seasons in tropical Thailand. Artificial insemination (AI) doses (n = 218) from 18 AI buffalo sires, prepared between 1980 and 1989 and 2003 and 2005, were tested and compared among three seasons, the rainy season, July-October; winter, November-February; and summer, March-June. The overall mean of DNA fragmentation index (DFI) (+/- SD) was 1.84 +/- 1.68%, range from 0.19 to 7.92%, with 0.221 +/- 0.021 of the x-DFI ranging from 0.190 to 0.350 and 0.023 +/- 0.009 of the SD-DFI ranging from 0.010 to 0.070. The DFI was consistently low (range 1.40 +/- 0.21% to 2.16 +/- 0.21%; LSM +/- SEM), with x-DFI ranging from 0.216 +/- 0.003 to 0.225 +/- 0.003 and SD-DFI ranging from 0.022 +/- 0.001 to 0.024 +/- 0.001 across the seasons. The DFI was low enough to be related to high fertility potential. However, DFI values varied statistically among seasons, being lower in the rainy season (1.40 +/- 0.21%, P < 0.05) than in winter (2.16 +/- 0.21%) or summer (2.00 +/- 0.20%), and were also affected by the year of semen collection and processing (P < 0.001). The proportion of morphologically abnormal sperm head shapes was low, with no significant differences between seasons. However, DFI was significantly related to the proportion of loose abnormal sperm heads (r = 0.27, P < 0.01). In conclusion, frozen-thawed swamp buffalo sperm chromatin integrity is not seriously damaged by cryopreservation or affected by the seasonal variations in temperature and humidity seen in tropical Thailand.

α-Tocopherol modifies tyrosine phosphorylation and capacitation-like state of cryopreserved porcine sperm

Sperm cryopreservation is associated with the production of reactive oxygen species (ROS) leading to membrane destabilization, which induces capacitation-like changes, increases protein tyrosine phosphorylation, and decreases their fertilizing ability. alpha-Tocopherol, a lipid peroxidation inhibitor, preserves the functionality of cryopreserved porcine sperm. Our aim was to evaluate the effect of alpha-tocopherol on sperm quality parameters as well as capacitation-like changes and modifications in protein tyrosine phosphorylation. Boar sperm frozen with or without 200 microg/mL of alpha-tocopherol were thawed and maintained at 37 degrees C for 10 min in BTS. Routine parameters of semen quality were evaluated by optical microscopy and membrane changes were determined by the epifluorescence chlortetracycline technique. Changes in protein tyrosine phosphorylation were examined using a specific anti-phosphotyrosine monoclonal antibody. Motility was higher (18%, P<0.05) in semen with alpha-tocopherol. Viability did not differ (P>0.05) between treatments. However, there was less (P<0.05) capacitation-like changes in semen with alpha-tocopherol compared to control samples. A MW 32 kDa tyrosine-phosphorylated protein was detected in extracts of cryopreserved sperm; the intensity of immunostaining was lower in semen containing alpha-tocopherol compared to the control (0.211+/-0.030 versus 0.441+/-0.034 arbitrary units). Additionally, this band was not detected in fresh sperm. The addition of alpha-tocopherol to the extender prior to cryopreservation of boar semen protected sperm membranes against oxidative damage and reduced both tyrosine phosphorylation and the capacitation-like state.

New staining methods for sperm evaluation estimated by microscopy and flow cytometry

New staining methods and automated instruments are now available to evaluate the sperm cell in vitro. Individual compartments of the sperm cell, such as the nucleus and the plasma and acrosomal membranes, may be investigated, as well as the cell function as shown by mitochondria activity and capacitation. Various probes are used and they can be analyzed by direct light or fluorescent microscopy or by flow cytometry. The automated instruments allow objective and accurate analysis and quantification as well as the ability to evaluate large population of cells in a shorter time, thus providing accurate evaluation of sperm quality. However, before these test can be recommended for routine clinical and investigational use, in the stallion, they need to be confirmed on a larger number of stallions and their correlation with traditional semen parameters and with stallion fertility has to be demonstrated.

DNA fragmentation assessment by flow cytometry and Sperm?Bos?Halomax (bright-field microscopy and fluorescence microscopy) in bull sperm

The aim of this study was to find the relationship between fertility (as 90-day non-return rates) and DNA fragmentation assessed by two techniques [sperm chromatin structure assay (SCSA) and Sperm-Bos-Halomax (SBH)]. Furthermore, other quality parameters were achieved (motility, morphological abnormalities, cytoplasmic droplets, viability, capacitation and acrosomal and mitochondrial status) and their correlations with fertility were analysed. Bulls were divided into three fertility groups: high [non-return rate (NRR) >or= 80], medium (80 < NRR >or= 70) and low (70 < NRR > 40). The results of this study indicate that there is a good correlation between fertility and different parameters of sperm quality (SBH and SCSA parameters, % of spermatozoa with head, neck and total abnormalities, and % of spermatozoa with proximal cytoplasmic droplets) and differences between fertility groups were observed in some of them (SBH and SCSA parameters and % of spermatozoa with head, neck and total abnormalities). In this sense, SBH parameters rendered good correlations with fertility (r = -0.42 using bright light microscope and r = -0.47 with fluorescence). Also, standard deviation of DNA fragmentation index (SD-DFI) and DFIh (cells with High DNA fragmentation index) showed good correlations with fertility (r = -0.41 and r = -0.29). No correlations were observed between SCSA and SBH parameters. A multiple regression shows that four parameters (% of proximal cytoplasmic droplets, % of intact acrosomes in total population, SD-DFI and percentage of fragmented DNA detected by bright light microscope) present a good predictive value of the fertility of sperm samples (r(2) = 0.34, p < 0.001).

Dialysis of boar semen prior to freezing-thawing: its effects on post-thaw sperm characteristics

Low-molecular weight components of the seminal plasma have a detrimental effect on sperm function. The present study was undertaken to evaluate the effect of the removal of low-molecular weight components by dialysis on sperm characteristics prior to and after freezing. Semen, collected from 5 boars, was extended in Kortowo-3 extender (K-3, Poland) and cooled for 3h (control non-dialysis) or dialyzed for 5h in semi-permeable dialysis bags of 12-14kDa molecular weight cut-off prior to freezing. The semen samples were diluted in lactose-hen egg yolk-glycerol extender (lactose-HEY-G) or lactose-lyophilized lipoprotein fractions-glycerol extender (lactose-LPFo-G), packaged into aluminum tubes and frozen in a controlled programmable freezer. Pre-frozen and frozen-thawed spermatozoa were evaluated for motility, plasma membrane (SYBR-14 and propidium iodide) and acrosome integrity, mitochondrial function (Rhodamine 123) and ATP content. The results of the study showed that dialysis significantly improved the sperm characteristics prior to freezing. Dialysis enhanced (P<0.05) post-thaw sperm motility, plasma membrane integrity and mitochondrial function, but had no significant effect (P>0.05) on recovery of spermatozoa with intact acrosomes. Furthermore, dialyzed spermatozoa exhibited higher (P<0.05) ATP content compared with the control after freezing-thawing. Consistent inter-boar variability was detected mainly in dialyzed semen following freezing-thawing. These results indicated that the improvement in sperm quality characteristics prior to freezing and the post-thaw sperm recovery were due to the removal of low-molecular weight components from the seminal plasma. It can be suggested that dialysis is effective in improving the post-thaw quality of boar spermatozoa and has also great practical importance in improving the protocols for cryopreservation of semen. Dialysis may also contribute to a better understanding of different mechanisms underlying cryo-induced damage to boar spermatozoa.

Combination of hypoosmotic swelling/eosin Y test for sperm membrane integrity evaluation: correlations with other sperm parameters to predict ICSI cycles

The objective of our study was to evaluate the accuracy of the combination of hypoosmotic swelling (HOS) and eosin Y (Ey) exclusion tests to predict the ICSI cycles' outcome and its correlations with other sperm parameters. The functional and structural integrity of sperm membrane was evaluated with the combined HOS/Ey test in 95 ICSI cycles and the results were correlated with other sperm parameters, including concentration, motility, strict morphology, and total motile sperm count. The combined HOS/Ey test was evaluated for the prediction of the ICSI cycles' outcome parameters including fertilization, cleavage, and pregnancy rates. The HOS/Ey test presented significant relationships with concentration, motility, and strict morphology (p < 0,0001) but it couldn't predict the fertilization, cleavage, and pregnancy outcomes of ICSI cycles. The combined HOS/Ey test has strong correlations with motility and strict morphology parameters of sperm samples but is not sufficiently sensitive to estimate the outcome of ICSI cycles.

Post-mortem semen cryopreservation and characterization in two different endangered gazelle species (Gazella gazella and Gazella dorcas) and one subspecies (Gazella gazelle acaiae)

Both Gazella gazella and Gazella dorcas are endangered species with continually dwindling population size, yet basic knowledge on their spermatozoa is missing. Semen collected post-mortem (PM) from the cauda epididymis of five adult gazelles (three Gazella gazella gazella, one Gazella gazella acaiae and one G. dorcas) was cryopreserved using directional freezing of large volumes (8 mL) with egg-yolk-free extender. Sperm size measurements and SYBR-14/propodium iodide (PI) viability stain validation for use in gazelles were conducted. Post-thaw characterization included motility, viability, acrosome damage evaluation, computerized motility characterization and morphology and sperm motility index (SMI) was calculated. Extracted sperm motility was 71.67+/-11.67% (mean+/-S.E.M.). Post-thaw motility ranged between 15% and 63%, viability was 57.49+/-3.24%, intact acrosome was detected in 63.74+/-2.6% (median 64.8%, upper/lower quartiles 71.79%, 61.82%), and normal morphology ranged between 41% and 63%. Motility characterization showed two sub-groups-highly active and progressively motile spermatozoa with SMI of 62.75+/-0.38 and low activity and poorly progressive with SMI of 46.16+/-1.53. Our results indicate that PM preservation of gazelle spermatozoa with satisfactory post-thaw viability is possible and cryobanking is achievable.

Sperm DNA damage is related to field fertility of semen from young Norwegian Red bulls

Flow cytometry was utilised for the first time to independently measure five sperm parameters of individual spermatozoa of bull ejaculates to differentiate between outcome successes after artificial insemination (AI). These parameters included plasma membrane and acrosome integrity, mitochondrial functionality and DNA damage measured by sperm chromatin structure assay (SCSA) and terminal deoxynucleotide transferase-mediated dUTP nick end labelling (TUNEL) assays. For each parameter, results of 142 ejaculates (30 bulls) were ranked into three groups according to their flow cytometric measures: (1) ejaculates with the 25% lowest measures; (2) the 50% middle measures; and (3) the 25% highest measures. In total, 20 272 first-service inseminations (18 × 106 spermatozoa per AI dose) were performed, where fertility was defined as non-return within 60 days after first insemination. While plasma membrane and acrosome integrity, and mitochondrial functionality were not significantly related to fertility, data from SCSA and TUNEL assays were significantly associated with fertility. Ejaculates in SCSA group 1 had higher odds of AI success (1.07, 95% CI = 1.02–1.12), whereas those in group 3 had lower odds of AI success (0.94, 95% CI = 0.89–0.99), compared with the average odds of all three groups. Ejaculates in group 2 did not have significantly higher odds of AI success compared with the average odds. For TUNEL-positive spermatozoa, the odds of AI success was higher in group 1 compared with the average odds (1.10, 95% CI = 1.02–1.13), whereas odds of AI success in groups 2 and 3 were not significant compared with the average odds. In conclusion, despite the high number of spermatozoa per AI dose from high-quality bulls, both SCSA and TUNEL assays were valuable measures in this study for evaluating sperm quality in relation to fertility after AI.

Comparison of in vitro laboratory analyses with the fertility of cryopreserved stallion spermatozoa

Assessing the fertilizing potential of a semen sample is important for effective stallion management and for rapid progress in evaluating new cryopreservation technologies. Unfortunately, sperm motility does not estimate fertility well. These experiments established assays to measure cell viability, acrosomal integrity and mitochondrial function for cryopreserved stallion spermatozoa, using flow cytometry, and determined the variability associated with these assays. Correlations between results for these laboratory assays and stallion fertility were also determined. The inter-assay variability for visual motility, computer assisted motility, and sperm velocity, sperm viability, percent viable-acrosome intact cells and mitochondrial function of cells were all similar, however, intra-assay variability was lower for flow cytometric assays than for motility assays. The reliability of all assays were >0.72, except for sperm velocity (0.32). Although visual motility and the straightness of sperm motility conducted 90 min after thawing were correlated with seasonal fertility (0.56 and 0.55, respectively), data from no single assay were correlated with first-cycle fertility rates (P > 0.05). Best models using data from multiple assays explained 66 to 73, 76 to 89 and 79 to 94% of the variability in fertilizing potential, when two, three and four variables were included, respectively. Caution is required in interpreting these data, as only a few stallions were evaluated and relatively few mares were bred to each stallion, however, they do indicate that using a few rapid and inexpensive sperm assays, we can begin to understand factors important in stallion sperm fertilizing capacity, and we can use these assays to more effectively evaluate new methods for cryopreserving stallion spermatozoa.

Mitochondrial activity of frozen-thawed spermatozoa assessed by MitoTracker Deep Red 633

The present study was conducted to find a more objective method of evaluating sperm quality than the current subjective motility evaluations by testing the applicability of a novel fluorescent probe, Mitotracker Deep Red 633 (M-22426), for measuring the mitochondrial activity of spermatozoa both after freezing/thawing (PT) and after swim-up selection (SU), using flow cytometry (FC). The results from FC were compared to those of conventional microscopic motility evaluations and of computer-assisted sperm analysis (CASA) as well as to the fertility obtained after AI in the field. Semen from six Estonian Holstein bulls, processed when the sires were aged 3, 5, and 7 years, was included in the experiment. Sperm motility (measured either subjectively or by means of CASA) was always significantly (p<0.01-0.001) higher in the spermatozoa recovered by SU, for any of the age groups considered, or even when combining the age groups. Motility (measured subjectively) after SU was significantly (p<0.05) higher when bulls reached 7 years of age, compared to earlier collection ages, but no differences were registered between ages for CASA-assessed motility, either after SU or immediately PT. The numbers of spermatozoa with high red fluorescence also increased after SU: p<0.05 (for semen from bulls aged 3 years), p<0.001 (5 years), p<0.001 (7 years), and p<0.001 when all age groups were combined. The proportion of spermatozoa with high mitochondrial activity as determined by Mitotracker Deep Red 633 correlated with sperm motility (p<0.01) both PT and after SU, but not with the fertility results. In conclusion, MitoTracker Deep Red 633 seems to be a reliable marker for frozen-thawed bovine semen viability both PT and after SU.

Alpha-tocopherol improves biochemical and dynamic parameters in cryopreserved boar semen

Cryopreservation is associated with the production of reactive oxygen species which lead to lipid peroxidation of sperm membranes. The objective was to determine an alpha-tocopherol concentration capable of improving the quality of cryopreserved porcine semen. Boar spermatozoa frozen with 200, 500 or 1000 microg/mL alpha-tocopherol were thawed and incubated at 37 degrees C for 4 h. Routine parameters of semen quality, susceptibility to lipid peroxidation 2-thiobarbituric acid (TBARS) and oxygen uptake were evaluated. Motility was higher (P<0.05) in samples treated with different concentrations of alpha-tocopherol up to 2 h of incubation. Viability and acrosome integrity significantly decreased during incubation (no significant differences between treatments). Two hundred micrograms per milliliter alpha-tocopherol protected spermatozoa against lipid peroxidation during incubation, but 1000 microg/mL failed to protect after 2 h of incubation. There was a negative association between TBARS and motility, suggesting that lipid peroxidation affected sperm motility. Both control and 200 microg/mL alpha-tocopherol samples preserved the capacity to generate oxidative energy up to 1 h of incubation. The addition of 200 microg/mL alpha-tocopherol in the semen extender could be useful to preserve boar spermatozoa against the oxidative stress generated by cryopreservation.

Assessment of boar semen quality in relation to fertility with special reference to methanol stress

The relationship between various semen evaluation tests and fertility in fertile and subfertile artificial insemination (AI) boars was examined. In total, 36 boars, 19 Finnish Landrace and 17 Yorkshire, were included. The average value of three ejaculates extended in an X-cell extender from each boar was used in the analysis. Based on nonreturn results (NR60d, later referred to nonreturn rate, NR%), the boars were divided into two groups: those with poor fertility (NR% < 80, n = 19) and those with normal or above average nonreturn rates (NR% = 83, n = 17). Semen quality was determined after 1 and 7 days of storage at 17 degrees C. Sperm motility before and after each methanol stress was assessed both subjectively and using a computer-assisted semen analyzer (CASA). The sperm cells were stained with calcein AM and propidium iodide and evaluated for plasma membrane integrity under an epifluorescence microscope. Propidium iodide and Hoechst 33258 dyes were used in parallel to stain sperm cells for fluorometric analysis with an automatic fluorometer. Sperm morphology was evaluated in stained smears. The percentage of sows reported as not having returned to estrus within 60 days after AI (nonreturn rate, NR%) and litter size of primiparous and multiparous farrowings were used as measures of fertility. Of the parameters analyzed, only CASA-assessed total sperm motility and methanol-stressed total sperm motility correlated significantly (P < 0.05) with nonreturn rate. Those tests presenting the highest correlation with nonreturn rate were CASA-assessed total motility (r = 0.54, P < 0.01) and subjective sperm motility (r = 0.52, P < 0.01) after 7 days of storage. The highest correlation with fertility at 1 day of storage was shown by methanol-stressed total sperm motility assessed with the CASA (r = 0.46, P < 0.01). The only semen parameter that correlated significantly (r = 0.37, P < 0.05) with litter size of multiparous farrowings was viability of seven-day stored semen stained with Hoechst 33258 and analyzed with a fluorometer. The methanol stress test described here could serve as a rapid test whose results could be used to predict NR% better than motility.

Comparison of methods to evaluate the plasmalemma of bovine sperm and their relationship with in vitro fertilization rate

The objectives of this study were to compare different methods of evaluating sperm plasmalemma and to determine their relationship with in vitro fertilization rate. A single batch of frozen semen from each of eight beef bulls was used for assessment of sperm viability and for in vitro fertilization. Conventional viability tests included sperm morphology, motility, acrosome integrity, and abnormal DNA condensation. Methods for evaluation of the sperm plasmalemma included eosin/nigrosin (EN) and trypan-blue (TB) vital stains, propidium iodide (PI) in combination with carboxyfluorescein diacetate (CFDA) or SYBR-14 (SYBR) fluorescent vital stains, and the hypoosmotic swelling test (HOST). A total of 133-150 oocytes were fertilized in vitro with sperm from each bull and cleavage rates were determined. There were high correlations between the results obtained with vital stains and good to excellent interclass correlation coefficients of agreement, indicating that these stains provide measures of the same sperm attribute, i.e. plasmalemma integrity. However, the proportions of membrane-intact sperm identified by EN or TB stains were greater (P<0.0001) than identified by CFDA/PI or SYBR/PI fluorescent stains. The results obtained with the HOST had moderate correlations but poor agreement with the results of the vital stains. The proportion of viable sperm identified by the HOST was lower (P<0.05) than the proportion identified by vital stains, indicating that response to the HOST did not depend only on the integrity of the plasmalemma. Although there were significant differences in fertilization rates and sperm viability among bulls, there was no sharp distinction for the results of sperm viability tests from bulls producing different in vitro fertilization rates. Proportions of normal, motile, acrosome-intact, and HOST-responsive sperm were identified as significant predictors of in vitro fertilizing potential; each of these endpoints explained 12-18% of the variation when evaluated separately (linear regression) and 48% when evaluated collectively (stepwise regression). In conclusion, EN and TB stains overestimated the proportion of plasmalemma-intact sperm compared to PI-based fluorescent stains. Vital stains evaluated the morphological integrity of the plasmalemma, whereas the HOST assessed plasmalemma function. In that regard, the HOST was the only plasmalemma evaluation method that significantly contributed to conventional sperm quality tests in predicting in vitro fertilization rate, indicating that the test could be incorporated to the routine of semen analysis.

Laboratory semen assessment and prediction of fertility: still utopia?

Finding a laboratory test reliable enough to predict the potential fertility of a given semen sample or a given sire for artificial insemination (AI) is still considered utopian, as indicated by the modest correlations seen between results obtained in vitro and field fertility. Male fertility is complex, and depends upon a heterogeneous population of spermatozoa interacting at various levels of the female genital tract, the vestments of the oocyte, and the oocyte itself. For this reason, laboratory assessment of semen must include the testing of most sperm attributes relevant for fertilization and embryo development, not only in individual spermatozoa but within a large sperm population as well. Strategies for the discovery of in vitro predictors of semen fertility require evaluations of low sperm doses for AI, so that differences in innate in vivo fertility can be accurately detected.

Assessment of sperm viability, mitochondrial activity, capacitation and acrosome intactness in extended boar semen during long-term storage

The purpose of this study was to assess sperm quality in extended boar semen during in vitro storage in order to determine which extender should be used and how long boar semen can be stored. Freshly ejaculated boar semen was diluted with equal volumes of Beltsville thaw solution (BTS), Androhep, KIEV or Zorlesco extenders and stored at 17 degrees C for up to 15 days. Sperm quality was evaluated by examining viability using SYBR-14/PI and Hoechst 33258 staining, mitochondrial activity using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1) staining, acrosome intactness by Coomassie blue staining, and capacitation status by chlortetracycline (CTC) staining. There were over 50% viable spermatozoa in boar semen extended with Zorlesco and Androhep extenders on Day 13 of storage. The percentage of JC-1-stained spermatozoa was 53.8 +/- 2.1% for Zorlesco and 57.7 +/- 1.60% for Androhep extenders on Day 13 of storage. The percentage of acrosome-intact spermatozoa detected by Coomassie blue staining was higher than that in the SYBR-14PI-, Hoechst 33258-, and JC-1-stained samples in our study. The results from SYBR-14/PI, Hoechst 33258, JC-1, and Coomassie blue staining were highly correlated (r > or = 0.9461). There were less than 15% capacitated spermatozoa in the semen extended with BTS, Androhep and Zorlesco extenders during 9 days of storage. However, most viable boar spermatozoa became capacitated by Day 13 of storage. The rank order of four extenders for maintaining sperm viability and mitochondrial activity was as follows: Androhep, Zorlesco, BTS, KIEV.

Cryopreservation in different concentrations of glycerol alters boar sperm and their membranes

To test the hypothesis that glycerol would concomitantly affect sperm membrane structure and the function of the intact cells, boar semen (4 ejaculates from 4 boars) was cryopreserved in an egg yolk extender with 0%, 2%, 4%, or 8% glycerol in 0.5-mL straws using previously derived optimal cooling and thawing rates. Increasing glycerol concentrations increased spermatozoal progressive motility immediately after thawing and after 2 hours at 43 degrees C, but decreased the percentage of sperm with normal acrosomal morphology. The mathematical products of the motility and acrosomal integrity scores (MOT x NAR index) were low in 0% and 8% glycerol, and significantly higher in 2% and 4% glycerol. The fluidity of sperm-head plasma membranes, a measure of molecular interaction, was assessed with the lipid probes trans-parinaric acid and cisparinaric acid (tPNA, cPNA), during a 2.5-hour incubation with or without 1 mM Ca2+. Membrane fluidity detected by each probe differed significantly, indicating the presence of at least 2 domains whose constituent molecules had unique dynamics. Behavior of each domain was radically altered by cryopreservation. Increasing glycerol concentration caused a variably faster loss of fluidity in the cPNA domain, and had highly variable effects on fluidity change over time in the tPNA domain. Normal acrosomal ridge (NAR) and the MOT x NAR index correlated significantly with the fluidity of the more mobile cPNA domain (+/- 1 mM Ca2+), supporting the hypothesis of an interrelationship of glycerol concentration during cryopreservation with sperm membrane structure and cell function. The MOT x NAR index may be a useful guide in choosing optimal cryoprotectant concentrations.

A novel automated fluorometric assay to evaluate sperm viability and fertility in dairy bulls

The artificial insemination (AI) industry is in need of an objective and rapid, but inexpensive method to evaluate frozen thawed bull semen ejaculates. This study presents a new fluorescence method that uses an automatized fluorometer and fluorophore stain propidium iodide that stains only those cells with damaged membranes. The fluorescence of the semen sample and the totally killed subsample were measured simultaneously, and viability was calculated. Every semen batch was analyzed before use in AI. For fertility evaluation, the nonreturn rates (NR%) obtained from 92,120 inseminations with the analyzed batches were recorded from 166 bulls (436 batches). This study confirms a 3.9% better NR% for the Finnish Holstein-Friesian breed than for Finnish Ayrshire. There was a clear seasonality in NR%: it differed (5.3%) significantly, being best in summer to autumn (June to October) and lowest in winter (January to March). The fluorometer method was fast and easy. The correlation between the total number of viable spermatozoa in an insemination dose and field fertility was low but significant (r = 0.051, P = 0.016), suggesting that the plasma membrane integrity evaluation can serve as a cost-beneficial quality control method of frozen-thawed semen at bull stations.

Fluorescent probes and flow cytometry to assess rat sperm integrity and mitochondrial function

Fluorescent assessment of cellular integrity and mitochondrial function by flow cytometry can provide a rapid and precise means of determining the functional status of large numbers of spermatozoa. In the present study, rat sperm viability was assessed with SYBR-14 and PI and sperm mitochondria were differentially labeled with JC-1. Sperm samples of variable viability were prepared using varying proportions of fresh and frozen spermatozoa. SYBR-14 stained sperm correlated well with expected sperm viability (r = 0.98). Motile sperm stained with JC-1 appeared orange in the midpiece indicating a high mitochondrial membrane potential whereas immotile sperm with a low membrane potential stained green. The percentage of spermatozoa staining orange was highly correlated (r = 0.99) with expected sperm viability. Flow cytometry using specific fluorescent probes is a useful technique for detecting changes in rat sperm plasma membrane integrity and mitochondrial function in large numbers of spermatozoa.

Assessment of equine sperm mitochondrial function using JC-1

The fluorescent carbocyanine dye, JC-1, labels mitochondria with high membrane potential orange and mitochondria with low membrane potential green. Evaluation of mitochondrial membrane potential with JC-1 has been used in a variety of cell types, including bull spermatozoa; however, JC-1 staining has not yet been reported for equine spermatozoa. The aim of this study was to apply JC-1 staining and assessment by flow cytometry or a fluorescence microplate reader for evaluation of mitochondrial function of equine spermatozoa. Six ejaculates from four stallions were collected and centrifuged through a Percoll gradient (PERC). Spermatozoa were resuspended to 25 x 10(6) cells/mL, samples were split, and one sample was repeatedly flash frozen (FF) in LN2 and thawed. The following gradients of PERC:FF were prepared: 100:0 (100), 75:25(75), 50:50 (50), 25:75 (25) and 0:100 (0). Samples were stained with 2.0 microM JC-1 and assessed for staining by flow cytometry and by a fluorescence microplate reader. A total of 10,000 gated events was analyzed per sample with flow cytometry. The mean percentage of cells staining orange for the 100, 75, 50, 25 and 0 treatments was 92.5, 72.8, 53.4, 27.3 and 7.3, respectively. The expected percentage of spermatozoa forming JC-1 aggregates was correlated with the actual percentage of orange labeled sperm cells determined by flow cytometry (r2=0.98). Conversely, JC-1 monomer formation was negatively correlated with expected mitochondrial membrane potential (r2=-0.98). The blank corrected orange fluorescence, assessed by microplate assay, was significantly (P<0.0001) correlated with the expected (r2=0.49) and with the flow cytometric (r2=0.50) determination of percentage of spermatozoa with mitochondria of high membrane potential. Total orange and orange:green fluorescence was also correlated with mitochondrial function. These results indicate that JC-1 staining can accurately detect changes in mitochondrial membrane potential of equine spermatozoa. The relative fluorescence of JC-1 labeling patterns of equine spermatozoa can be accurately and objectively determined by flow cytometry and by a fluorescence microplate reader assay.

Flow cytometric evaluation of antibiotic effects on viability and mitochondrial function of refrigerated spermatozoa of Nile tilapia

Improved techniques for storage and evaluation of fish sperm would enhance breeding programs around the world. The goal of this study was to test the effect of antibiotics on refrigerated sperm from Nile tilapia (Oreochromis niloticus) by use of flow cytometry with 2 dual-staining protocols for objective assessment of sperm quality. Concentrations of 1 x 10(9). sperm/mL were suspended in Ringer's buffer at 318 mOsmol/kg (pH 8.0). The fluorescent stains Sybr 14 (10 microM), propidium iodide (2.4 mM), and rhodamine 123 (0.13 microM) were used to assess cell viability and mitochondrial function. Three concentrations of ampicillin, gentamicin, and an antibiotic/antimycotic solution were added to fresh spermatozoa. Motility estimates and flow cytometry measurements were made daily during 7 d of refrigerated storage (4 degrees C). The highest concentrations of gentamicin and antibiotic/antimycotic and all 3 concentrations of ampicillin significantly reduced sperm viability. The highest of each of the 3 antibiotic concentrations significantly reduced mitochondrial function. This study demonstrates that objective sperm quality assessments can be made using flow cytometry and that addition of antibiotics at appropriate concentrations can lengthen refrigerated storage time for tilapia spermatozoa. With minor modifications, these protocols can be adapted for use with sperm from other species and with other tissue types.

In vitro comparison of fowl sperm viability in ejaculates frozen by three different techniques and relationship with subsequent fertility in vivo

A series of experiments was conducted to compare the viability of fresh fowl spermatozoa, samples suspended in three cryoprotectants (CPAs), frozen/thawed samples, and frozen/thawed samples maintained in vitro for up to 24 h. The CPAs used were glycerol (Glyc), dimethylacetamide (DMA), and dimethylformamide (DMF). Viability was assayed using two double stains, Eosin + Nigrosin or SYBR-14 + PI (propidium iodide). Semen samples examined with SYBR-14 + PI indicated significant differences in viability between fresh and ready-to-freeze preparations (fresh, 83%; Glyc, 73%; DMA, 74%; DMF, 72%; P < 0.05). In contrast, Eosin + Nigrosin did not detect any difference at this stage (fresh, 88%; Glyc, 86%; DMA, 87%; DMF, 88%; P > 0.05). The percentages of viable spermatozoa in frozen/thawed ejaculates stored in vitro for 0, 4, and 24 h were generally higher in samples treated with glycerol than in those treated with DMA or DMF, irrespective of the technique used to assess sperm viability (P < 0.05). Fertility in eggs obtained from hens inseminated with semen frozen in DMA reached levels comparable to those obtained from hens inseminated with fresh undiluted semen (88 and 93%, respectively; P > 0.05). In contrast, fertility of eggs from hens inseminated with semen frozen in DMF or glycerol was significantly lower, although still very good, than that observed in eggs from hens inseminated with semen frozen/thawed in DMA (79 and 76%, respectively; P < 0.05). Finally, the double stain SYBR-14 + PI was proven more effective than Eosin + Nigrosin to assess sperm viability in fresh, stored, and frozen fowl semen. However, additional tests (e.g., morphology, acrosomal status, motility) remain necessary to develop a working model of in vitro sperm analysis capable of revealing the fertilizing potential of fresh and frozen fowl spermatozoa.

Viability assessment of honey bee, Apis mellifera, sperm using dual fluorescent staining

Since the development of instrumental insemination of honey bee (Apis mellifera) queens in the 1930s, there has been interest in the evaluation and in vitro storage of semen. Several fluorescent stains, when used in combination, have been effectively used to assess sperm viability in mammalian and avian species. Our objectives were to test two combinations of living:dead fluorescent stains, SYBR-14 with propidium iodide (PI), or Calcein-AM with PI, and validate the use of these probes with honey bee sperm. SYBR-14 is a nuclear stain producing green fluorescence of the DNA in living sperm, Calcein-AM is a membrane-permeant esterase substrate staining entire sperm green, and PI is a traditional dead cell stain giving a contrasting red color. Both living stains fluoresced bee sperm, but the SYBR-14:PI produced a clearer distinction between the living and dead sperm. A graduated series of known living:dead sperm proportions was used to validate the accuracy of the stains for determining sperm viability in honey bees.

Viability assessment of dog spermatozoa using flow cytometry

The percentages of living and dead spermatozoa in fresh dog semen samples were assessed by means of a dual staining technique using carboxifluorescein diacetate (CFDA) and propidium iodide (PI). Two ejaculates were obtained from dogs, each ejaculate was divided into 4 aliquots, and different proportions of freeze-killed cells were added to each aliquot. Data obtained by flow cytometry analysis of each sample were compared with those obtained by the microscopic evaluation under epifluorescence illumination and by phase-contrast microscopy evaluation of the samples stained with eosin-nigrosin. Regression analysis was used to compare the 3 methods for membrane integrity assessment of canine spermatozoa, and high correlation coefficients were found between the flow cytometry procedure and the 2 microscopy techniques. The results from this study validate the use of flow cytometry as a precise method for assessing the viability of dog spermatozoa.

Comparison of assessment of fowl sperm viability by eosin-nigrosin and dual fluorescence (SYBR-14/PI)

The kinetics of fowl sperm viability/mortality following short-term and long-term in vitro storage were studied using 2 different staining methods: eosin/nigrosin (observed under light microscopy) and SYBR-14/PI (dual fluorescence). Based on data obtained at 0, 30 min and at 2, 4 and 24 h (T0, T30, T2, T4, and T24) after in vitro storage (4 degrees C, agitated) of fresh or frozen-thawed semen, the dual association SYBR-14/PI was more effective than eosin/nigrosin (P < 0.05) staining for the detection of sperm viability/mortality at early stages (30 min) in nonfrozen ejaculates stored above 0 degree C. In cryopreserved preparations, the 2 techniques were comparable for assessing viable spermatozoa immediately after thawing, but higher percentages (P < 0.05) of nonviable spermatozoa were detected by the SYBR-14/PI procedure for up to 4 h of in vitro storage post thawing (4 degrees C, agitated). Finally, comparable results were observed between the 2 techniques 24 h after beginning in vitro storage post thawing. It is concluded that the dual association SYBR-14/PI procedure is more effective (or, at least, more rapid) than eosin/nigrosin staining for the assessment of sperm viability/mortality in both fresh and cryopreserved samples of fowl semen. However, in the latter case, the thawing stage needs to be followed by a period of in vitro storage lasting at least 4 h to allow for easier discrimination between viable and nonviable populations of spermatozoa.

Quantification of bull sperm characteristics measured by computer-assisted sperm analysis (CASA) and the relationship to fertility

Two experiments were conducted to evaluate semen quality of bulls housed under controlled conditions at a large AI facility and relate results to fertility. In Experiment 1 semen was collected from six 6-yr-old bulls twice daily at 3- to 4-d intervals for 3 d. In Experiment 2 eleven 6- to 11-yr-old bulls were used. Extensive breeding information was available and semen was collected as in Experiment 1 but replicated 4 times. Standard semen analysis and computer-assisted sperm analysis (CASA) with the Hamilton Thorne IVOS, model 10 unit, were performed on 36 first and second ejaculates in Experiment 1 and on 44 first ejaculates in Experiment 2. Sixteen fields (2 chambers with 8 fields per chamber) were examined per sample. In Experiment 1 the correlation between estimated sperm concentration by spectrophotometry and CASA was 0.91 (P < 0.01). Among bulls the range in the percentage of motile spermatozoa was 52 to 82 for CASA versus 62 to 69 for subjective measurements made by highly experienced technicians. Thus, CASA, with high repeatability, provided a more discriminating estimate of the percentage of motile sperm cells than did the subjective procedure. Bull effect was much greater than any other variable in the experiments. Chamber differences were small and so the results for the 2 chambers with 8 fields each were combined. One to five CASA values were correlated with bull fertility, defined as 59-day nonreturn rates corrected for cow and herd effects. The percentage of motile spermatozoa accounted for a small fraction of the total variation in fertility (r2 = 0.34). However higher r2 values (0.68 to 0.98) were obtained for 2 to 5 variables used in the multiple regression equations. The results are promising, and further testing will determine more precisely which of these CASA variables are most useful in estimating bull fertility potential.

Viability assessment of turkey sperm using fluorescent staining and flow cytometry

Turkey sperm viability was evaluated using several fluorescent stains both singularly and in combination. Dilution curves and several extenders were used to determine optimal stain concentrations. Semen was collected from eight toms, pooled, diluted, stained, and evaluated microscopically within 2 h of collection. Replicates were assessed for both viable and nonviable sperm (green and red fluorescence, respectively) using flow cytometry. SYBR-14, which likely requires membrane potential for optimal fluorescence, or Calcein AM (CAL), which assesses the membrane integrity of cells (both green fluorescence), in combination with propidium iodide (PI) to stain the dead or degenerating cells (red fluorescence) provided optimal results. Sperm were killed by unprotected freeze-thawing to provide mixed aliquots containing known amounts of fresh:killed sperm. The percentage of viable sperm, as determined by SYBR-14 with PI or CAL with PI staining, were 76.6, 58.8, 39.3, 20.1, 8, and 73.5, 55.8, 36.0, 17.1, .4, respectively, for ratios of 100:0, 75: 25, 50:50, 25:75, and 0:100 of fresh:killed mixtures. Semen from 30 individual toms was collected on 2 d and examined in replicate using these staining combinations. The proportion of viable sperm, as indicated by uptake of SYBR-14 or CAL stain, ranged from 55.8 to 86.7 and 38.0 to 86.1, respectively. Staining combinations were effective in estimating the viability of turkey sperm and could be useful for monitoring sperm viability before and after storage.