Evaluation of post-thaw Asian elephant (Elephas maximus) spermatozoa using flow cytometry: the effects of extender and cryoprotectant

Although the development of semen cryopreservation in the African elephants (Loxodonta africana) has been accomplished, effective procedures for cryopreservation of Asian elephant (Elephas maximus) spermatozoa have not been established. In the present study, we investigate the freezing methods for conservation of Asian elephant spermatozoa under field conditions and identify the most suitable freezing protocols which provide acceptable post-thaw semen quality. Semen was collected from two Asian elephant bulls (EM1 and EM2, 10 ejaculates from each bull) by manual manipulation and were assessed for volume, pH, sperm cell concentration, and progressive motility. Eight out of 20 ejaculates were of acceptable quality (progressive motility >/= 60%), and were used for cryopreservation studies. Semen were frozen in TEST + glycerol, TEST + DMSO, HEPT + glycerol, or HEPT + DMSO. The post-thaw progressive sperm motilities were assessed, and sperm cells were stained with PI and FITC-PNA for membrane and acrosomal integrity assessment using flow cytometry. Post-thaw progressive motility of spermatozoa (EM1: 42.0 +/- 4.3%; EM2: 26.0 +/- 17.3%) and the percentage of membrane and acrosome intact spermatozoa (EM1: 55.5 +/- 8.1%; EM2: 46.3 +/- 6.4%) cryopreserved in TEST + glycerol were significantly higher than (P < 0.05) those frozen in the other medium investigated choices for cryopreservation of Asian elephant spermatozoa. The data support the use of TEST + glycerol as an acceptable cryopreservation media of Asian elephant semen for the establishment of sperm banks.     

The effect of antioxidants on motility, viability, acrosome integrity and DNA integrity of frozen-thawed epididymal cat spermatozoa

Antioxidants partially ameliorated the negative effects of reactive oxygen species (ROS) produced during cryopreservation. The objective of the present study was to investigate the effect of cysteine and a water-soluble vitamin E analogue on the quality of frozen-thawed epididymal cat spermatozoa. Epididymal spermatozoa were collected from eight male cats and divided into three aliquots; these were resuspended with a tris egg yolk extender I (EE-I), or the same extender supplemented with 5mM dl-cysteine (EE-C) or with 5mM of a water-soluble vitamin E analogue (EE-Ve). Prior to the freezing step, sperm suspensions were added to the extender with Equex STM paste (EE-II). Sperm motility, progressive motility, membrane integrity, and acrosome status were evaluated at collection, after cooling, and at 0, 2, 4, and 6h post-thaw. Sperm DNA integrity was evaluated at 0 and 6h post-thaw. Relative to the control group, supplementation with vitamin E improved (P<0.05) post-thaw motility (69.4+/-5.6%), progressive motility (3.9+/-0.3), and membrane integrity (65.1+/-8.1%) immediately after thawing, whereas cysteine supplementation improved (P<0.05) post-thaw motility after 2h of incubation (53.8+/-12.2%) and DNA integrity after 6h (84.1+/-4.4%). However, neither antioxidant significantly increased the acrosome integrity of frozen-thawed spermatozoa. In conclusion, cysteine or vitamin E supplementation of tris egg yolk extender improved motility, progressive motility and integrity of the sperm membrane and DNA of frozen-thawed epididymal cat spermatozoa.     

Cryopreservation of goat spermatozoa: comparison of two freezing extenders based on post-thaw sperm quality and fertility rates after artificial insemination

TRIS-glucose or skim milk extenders are most commonly used for cryopreserving goat sperm. The aim of this study was to compare the ability of two extenders based on TRIS and skimmed milk buffer to maintain sperm viability after cryopreservation. Goat semen samples (n=110) were frozen with TRIS and with milk extender and thaw. Sperm motion parameters, morphology and acrosomal integrity were assessed in fresh and frozen-thawed samples by Sperm Class Analyzer (SCA) and Diff-Quik and Spermac staining techniques. Pregnancy rates were obtained after cervical insemination with frozen semen doses. The cryopreservation process had a significant effect on acrosome and kinematic parameters. TRIS extender provided more effective preservation of total motility, velocity parameters and amplitude of lateral head displacement after freezing. The percentage of acrosome intact spermatozoa was significantly higher in samples diluted with milk extender. In the insemination doses, mean values of velocity parameters and lateral head displacement were higher in doses processed in TRIS. Spermatozoa frozen in milk extender was mathematically greater than for those frozen with TRIS extenders, though no significant difference exists. We conclude that post-thaw kinematic parameters and acrosome integrity assessed after 1h of incubation was acceptable in both extenders which indicated the feasibility of cryopreserving goat spermatozoa. TRIS extender results in better in vitro performance compared to milk, though these improvements were not reflected in fertility results. Semen doses cryopreserved in milk extender provided greater pregnancy rates after intra-cervical insemination compared to those in TRIS extender (52.4% versus 42.9%).     

Use of image analysis to assess the plasma membrane integrity of ram spermatozoa in different diluents

Sperm membrane integrity can be assessed by examining a large number of fluorochrome-stained sperm cells over a relative short period of time by flow cytometry or fluorimetry. However, many small laboratories lack a flow-cytometer or fluorimeter for sperm analysis. This study was designed to develop a new image analysis method to evaluate the membrane integrity of ram spermatozoa with the aid of open software, and was divided into three experiments. In the first experiment, the new computer-assisted method was validated by mixing fresh semen samples with different volumes of killed semen in order to know the proportions of damaged spermatozoa in the samples. In the second trial, the new method was compared with the traditional manual counting, and the effect of three extender media on the suitability of the new developed method was evaluated. In the third experiment, the method proposed was tested by comparing the use of milk-, citrate- or TRIS-based diluents for ram semen preservation at 15 degrees C. In all experiments, semen was assessed for plasma membrane integrity and for percentage of motile and progressive sperm by CASA. In the new computer-assisted method, two images of the sperm cells in a given microscopy field are captured and the number of total- and membrane-damaged cells counted. In the first trial, proportions of damaged sperm cells in each sample determined by the automated procedure agreed closely (r2=0.98, P<0.001) with the predicted theoretical values. In experiment 2, the results of membrane integrity obtained using the new method were highly correlated with those provided by the conventional manual counting after PI-CFDA double staining (r=0.99, P<0.001), and also correlated with sperm motility and progressive motility percentages. Viability was significantly higher after dilution with citrate-, than with Tris-based medium, but similar to PBS (70.32+/-3.93, 55.48+/-5.76 and 65.38+/-3.15, respectively), After 0, 24 and 48h of storage, significantly higher percentages of motile, progressive, and membrane-intact spermatozoa were recorded for the milk than for the Tris extenders. Our results validate the new computer-assisted method for assessing sperm membrane integrity in the sheep, and indicate that the milk extender is less damaging to the sperm of this species than citrate or Tris extenders.     

Freezing African Elephant Semen as a New Population Management Tool

Background

The captive elephant population is not self-sustaining and with a limited number of breeding bulls, its genetic diversity is in decline. One way to overcome this is to import young and healthy animals from the wild. We introduce here a more sustainable alternative method - importation of semen from wild bulls without removing them from their natural habitat. Due to the logistics involved, the only practical option would be to transport cryopreserved sperm. Despite some early reports on African elephant semen cryopreservation, the utility of this new population management tool has not been evaluated.

Methodology/Principal Findings

Semen was collected by electroejaculation from 14 wild African savanna elephant (Loxodonta africana) bulls and cryopreserved using the directional freezing technique. Sperm treatments evaluated included the need for centrifugation, the use of hen or quail yolk, the concentration of glycerol (3%, 5% or 7%) in the extender, and maintenance of motility over time after thawing. Our results suggest that dilution in an extender containing hen yolk and 7% glycerol after centrifugation best preserved post-thaw sperm motility when compared to all other treatments (P≤0.012 for all). Using this approach we were able to achieve after thawing (mean ± SD) 54.6±3.9% motility, 85.3±2.4% acrosome integrity, and 86.8±4.6% normal morphology with no decrease in motility over 1 h incubation at 37°C. Sperm cryopreserved during this study has already lead to a pregnancy of a captive female elephant following artificial insemination.

Conclusions/Significance

With working techniques for artificial insemination and sperm cryopreservation of both African and Asian elephants in hand, population managers can now enrich captive or isolated wild elephant populations without removing valuable individuals from their natural habitat.     

Comparison of an extender containing defined milk protein fractions with a skim milk-based extender for storage of equine semen at 5 degrees C

A problem of semen extenders based on milk or egg yolk is the fact that these biological products consist of a variety of substances. Extenders containing only components with clearly protective effects on spermatozoa would thus be an advantage. In this study, we have compared the effects of an extender containing defined caseinates and whey proteins only (EquiPro, defined milk protein extender) with skim milk extender on equine spermatozoa during cooled storage. The defined milk protein extender was used with and without the antioxidant N-acetyl cysteine (NAC). In a second experiment, semen was diluted with PBS or defined milk protein extender and was either stored directly or 90% of seminal plasma was removed by centrifugation and replaced by defined milk protein extender before storage. In both experiments, eight stallions were available for semen collections. Motility, velocity and membrane integrity of spermatozoa were determined by CASA immediately after semen processing and after 24, 48 and 72 h of storage at 5 degrees C. Total motility after 24 h of storage was lowest in semen diluted with PBS (p<0.05 versus all extenders). At 48 and 72 h, motility of spermatozoa in defined milk protein extender was significantly (p<0.05) higher than in PBS or skim milk extender. Velocity of spermatozoa after storage was highest in defined milk protein extender. Membrane integrity after storage was significantly (p<0.05) lower in semen diluted with PBS than in semen diluted with both extenders. Addition of NAC was without effect on the examined parameters. Centrifugation further increased the percentage of motile and membrane-intact spermatozoa in the defined milk protein extender (p<0.05). Velocity of spermatozoa in this extender was not negatively affected by centrifugation.     

Effects of antioxidants on motility and membrane integrity of chilled-stored stallion semen

The use of chilled-stored stallion semen is limited by its relatively short-term fertilizing capacity. An important reason for the decrease in fertility during storage is the peroxidation of sperm membrane lipids. In this study, effects of the antioxidants ascorbic acid (0.45 and 0.9 g/L) and catalase (0.45 x 10(6) and 1.8 x 10(6) units/L) on chilled-stored stallion semen were investigated. Semen was collected by artificial vagina from 7 stallions and was diluted with skim milk extender or glycin extender. Sperm motility and membrane integrity were investigated after dilution and after 24, 48 and 72 h at 5 degrees C. Ascorbic acid significantly increased the percentage of membrane-intact spermatozoa at 24, 48 and 72 h at 5 degrees C when compared with that of the controls (P < 0.05), irrespective of the extender. Ascorbic acid decreased the percentage of progressively motile spermatozoa (P < 0.05) at a concentration of 0.9 g/L in glycin extender. Catalase decreased (P < 0.05) progressively motile spermatozoa after 24, 48 and 72 h at 5 degrees C in skim milk extender at a concentration of 1.8 x 10(6) units/L. Catalase decreased (P < 0.05) the percentage of membrane-intact spermatozoa at 24 h. Motility and membrane integrity of spermatozoa after dilution with glycin extender containing catalase did not differ from the controls. In conclusion, ascorbic acid has protective effects on sperm membrane integrity in diluted stallion semen.     

Usefulness of powdered and fresh egg yolk for cryopreservation of Zebu bull spermatozoa

This experiment was designed to compare powdered egg yolk with fresh egg yolk in an extender for cryopreservation of Zebu bull semen. Sperm motility, plasma membrane integrity and viability were assessed at different stages of cryopreservation (post-dilution, pre-freezing and post-thawing). Sperm plasma membrane integrity remained similar at all the stages of cryopreservation. Sperm motility and viability were significantly higher after thawing in the extender containing powdered egg yolk. In conclusion, powdered egg yolk may be used in an extender for the cryopreservation of Zebu bull spermatozoa.     

Effect of filtration on post-thaw quality of bull semen

Semen from 4 Holstein bulls was diluted in 4 different extenders, filtered with Sephadex ion-exchange column, and frozen in liquid nitrogen. Sperm motility, progressive motility, path velocity, progressive velocity and the percentage of normal acrosomes of filtered and nonfiltered semen were recorded before and after freezing. Semen characteristics were significantly influenced by extender, filtration and freezing. Before and after freezing, motility measurements and the percentage of normal acrosomes were higher (P < 0.001) in filtered than in nonfiltered spermatozoa. Post-thaw recovery rate of motile spermatozoa was higher in filtered semen than nonfiltered (68 vs 39%, P < 0.0001). The reduction in motility, progressive motility and the percentage of normal acrosomes during freezing and thawing processes were significantly lower (P < 0.0001) in filtered semen (34, 34 and 4%, respectively) than nonfiltered (59, 54 and 15%, respectively). Post-thaw viability of spermatozoa was significantly affected by extender, filtration and time (P < 0.0001). Immediate (0 h) post-thaw motility of nonfiltered semen (29%) was similar to 4-h post-thaw motility of filtered semen (25%; P > 0.05). In conclusion, bull spermatozoa recovered by Sephadex ion-exchange filtration showed better post-thaw viability.     

The effect of different extenders on post-thaw sperm survival, acrosomal integrity and longevity in cryopreserved semen of Formosan Sika deer and Formosan Sambar deer

This study investigates the efficacy of five extenders in contributing to the outcome of semen cryopreservation in Formosan Sika and Sambar deer. Pooled semen (n=4) of six males of each breed was used. In Sika deer, semen collection rate was 96% (23/24) over all electro-ejaculations. Volume, sperm motility and sperm concentration of fresh ejaculates was 0.5+/-0.4 ml, 77+/-6% and 1471.3+/-940.0 x 10(6) ml(-1), respectively. Post-thaw motility in respective extender was A: 66+/-16%; B: 71+/-2%; C: 73+/-6%; D: 9+/-4% and E: 26+/-12% (mean+/-S.D.). In extender C (74+/-14%) more viable spermatozoa were preserved than in the others (A: 64+/-10%; B: 48+/-11%; D: 41+/-16%; E: 47+/-6%; P<0.05). Acrosomal integrity was not influenced by extender composition. Post-thaw motility did not decrease during a 4-h incubation period, irrespective of the extender used (P>0.05). In Sambar deer, semen collection rate was 88% (21/24) over all electro-ejaculations. Volume, sperm motility and sperm concentration of fresh ejaculates was 1.3+/-0.5 ml, 82+/-4% and 379.1+/-252.2 x 10(6) ml(-1), respectively. Post-thaw motility was in respective extenders A: 69+/-2%; B: 74+/-6%; C: 73+/-2%; D: 13+/-6% and E: 31+/-20%. Extenders B and C were superior (P>0.05) with respect to sperm motility. Similarly, post-thaw viability in extenders A (70+/-7%), B (76+/-7%) and C (79+/-2%) was higher than that D (25+/-19%) and E (29+/-17%) (P<0.01). Sperm acrosomal integrity was better preserved in extenders B (86+/-4%) and C (83+/-4%) than in extenders A (54+/-13%), D (39+/-22%) and E (46+/-22%) (P<0.05). Post-thaw sperm longevity in extender A reduced from 69 to 16% during incubation (P<0.05) whereas only a slight decrease was observed in the other extenders after 4 h. In conclusion these data show that egg-yolk-Tris-Tes-glycerol based extender C containing Equex STM paste is optimal for freezing semen of Formosan Sika deer while egg-yolk-Tris-citric acid-glycerol based extender B containing Equex and extender C are superior in semen cryopreservation to others for Formosan Sambar deer.     

Viability and fertility of rabbit spermatozoa diluted in Tris-buffer extenders and stored at 15 degrees C

Artificial insemination (AI) in rabbits is not extensive in the breeding programs of the rabbit meat industry. A limiting factor is related to the semen preservation. In order to improve the use of AI, two experiments have been conducted to evaluate sperm viability and fertility of rabbit semen chilled and stored at 15 degrees C after dilution in Tris-based extenders. In Experiment 1, pooled semen samples were diluted 1:10 (semen/extender) in four different Tris-based extenders (Tris-citric-glucose (TCG), TES-Tris-glucose (TTG), Tris-citric-fructose (TCF) and TES-Tris-fructose (TTF)) and stored at 15 degrees C. Sperm viability was evaluated at 0, 24, 48, 72 and 96 h following dilution for total sperm motility (TSM), forward progressive motility (FPM), plasma membrane integrity (PMI) and acrosome integrity (NAR). Viability of spermatozoa declined with time of storage (P<0.05), irrespective of the extender used. There were interactions between extender and time of storage (P<0.05) in all viability parameters evaluated. After 96 h of storage, TCG provided the highest sperm viability (P<0.05) and TTG the lowest (P>0.05). In Experiment 2, a field trial was conducted at a commercial farm to evaluate the conception and farrowing rates of rabbit spermatozoa extended in TCG. After synchronization of oestrous and induction of ovulation, 3713 does with different physiological conditions (nulliparous, primiparous, lactating and re-breeding) were inseminated one time (15x10(6) sperm per doses) with semen stored at 0 (n: 1275), 24 (n: 1503) and 48 h (n: 935) at 15 degrees C. Overall conception and farrowing rates were 77.1+/-0.7 and 70.4+/-0.7, respectively, and the mean litter size was 7.6+/-0.1. Fertility results were unaffected by the time of semen storage (P>0.05). Regardless of time of semen storage, fertility results were affected by the physiological conditions of does (P<0.05). Nulliparous and lactating does showed the highest fertility and primiparous the lowest. In summary, these results indicate that Tris-buffer extenders are effective for preserving viability and fertilizing capability of rabbit spermatozoa stored at 15 degrees C.     

Effects of the supplementation of trehalose extender containing egg yolk with sodium dodecyl sulfate on the freezability of goat spermatozoa

Two experiments were conducted to determine the effect of sodium dodecyl sulfate (SDS) added to a trehalose-egg yolk extender on the cryopreservation of goat spermatozoa. In Experiment 1, semen from four goats was frozen in trehalose extender (osmolality = 370, pH = 7) containing 4 and 20% (v/v) glycerol and egg yolk, respectively, and 0.035-0.2% SDS. After thawing, sperm motility and acrosome integrity were assessed using a computer-assisted sperm analysis (CASA) system and fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA). Both motility and progressive motility were improved (P < 0.05) by increasing the concentration of SDS in the trehalose-egg yolk extender, with the best results obtained with SDS at 0.1% (80.0 +/- 1.5% and 65.0 +/- 1.7%, respectively). There were no significant differences in path velocity when spermatozoa were frozen in a diluent containing 0.035, 0.05, 0.075, or 0.1% SDS, but path velocity decreased significantly with 0.2% SDS. The percentage of acrosome-intact sperm were highest (P < 0.05) when 0.05% (74.0 +/- 1.1) and 0.075% (70.0 +/- 1.2) SDS were used. In Experiment 2, the effect of diluent storage time (6, 24, or 48 h) before freezing on the cryoprotective effect of SDS was investigated. Prolonged storage of the diluent had slight cryoprotective effects when 0.2% SDS is used, while motility and the acrosome integrity of the cryopreserved spermatozoa improved slightly when the extender was stored for 48 h at 5 degrees C before use. In conclusion, goat sperm freezability was significantly improved when sperm were frozen in a trehalose-egg yolk extender containing an adequate concentration of SDS.     

Long-term preservation of chilled canine semen: effect of commercial and laboratory prepared extenders

The present study was conducted to evaluate chilled semen conservation over time in 3 commercial and 4 laboratory prepared extenders, including a new Tris-glucose extender. The beneficial effect of adding egg yolk to these media was also analyzed. The effects of these extenders on motility and acrosome reaction were characterized objectively using a computer-aided semen analyzer and the chlortetracycline staining, respectively. No significant differences were observed when comparing the different commercial extenders without egg yolk, but addition of egg yolk improved all motility parameters significantly (preservation of 50% of motility was observed at 3.2+/-1, 2.9+/-0.5, 2.3+/-0.5, 8.5+/-0.2, 5.4+/-1.1, 5.2+/-0.4 d, for Biladyl, green extender and fresh-phos extenders without and with egg yolk, respectively). Motility parameters were best preserved in egg yolk supplemented Biladyl extender with a mean percentage of 86.3+/-10.5 motile spermatozoa after 7 d at 4 degrees C. Efficacy of egg yolk-supplemented commercial extenders on sperm motility at 4 degrees C was (in decreasing order) as follows: Biladyl > green extender > fresh-phos. However, high quality motility and the percentage of motile spermatozoa were highest with some of the laboratory prepared extenders: a 50% conservation rate of motile spermatozoa was observed following the use of supplemented egg yolk extenders. These are classified in decreasing order as follows: Tris-glucose (13+/-1 d) > Tris-fructose (9.7+/-0.6) > EDTA (4.+/-0.6 d) > Tris-bes (3.6+/-1.1 d). A low concentration of motile spermatozoa was still observed in the Tris-glucose egg yolk extender 16 d after collection, clearly demonstrating the importance of the medium and the beneficial effect of egg yolk on sperm motility of 4 degrees C chilled semen. Similar effects of extender were observed for acrosome reactions. Egg yolk clearly had a protective effect reducing acrosome reactions significantly in all media tested as follows: the highest acrosome losses were observed in the fresh-phos and EDTA extenders without egg yolk; the lowest rate was observed with Tris-glucose supplemented egg yolk extender. In conclusion, at 4 degrees C, egg yolk extender best-protected sperm motility parameters. Differences in osmolarity between the extenders in terms of substrate related to sperm metabolic activity may explain the optimal results obtained using egg yolk-supplemented Tris-glucose extender, which preserved motility and acrosome integrity in chilled dog semen. These results indicated that good quality dog spermatozoa could be preserved for up to 10 d.     

Quality and fertilizing ability of electroejaculated cat spermatozoa frozen with or without Equex STM Paste

An optimal protocol for cat semen cryopreservation has not yet been defined. Addition of Equex STM Paste has been tested for epididymal cat spermatozoa but not for ejaculated cat spermatozoa. Furthermore, the effect of Equex STM Paste on fertilizing ability of cryopreserved semen has never been evaluated in that species. Therefore, the aims of the current study were to investigate if addition of Equex STM Paste to a freezing extender for electroejaculated cat (Felis catus) semen would improve postthaw sperm quality and if sperm fertilizing ability after cryopreservation with or without Equex STM Paste was preserved. Semen was collected by electroejaculation and frozen in a Tris-glucose-citrate egg yolk extender supplemented with (0.5% vol/vol) or without Equex STM Paste. In Experiment 1, sperm motility, membrane integrity, and acrosomal status were determined immediately after collection and at 0, 3, and 6 h postthaw. In Experiment 2, frozen semen from the two groups was used for in vitro fertilization (IVF) of in vitro-matured cat oocytes. Cleavage rate was recorded 30 h after IVF, and embryo development was evaluated on Days 6 and 7 of culture. In Experiment 1, the rate of motile spermatozoa after freezing-thawing was higher when Equex STM Paste was added to the freezing extender, but progressive motility score was not influenced (P > 0.05). Sperm membrane integrity was positively affected (P < 0.05) by the addition of the detergent. Intact acrosomes after thawing were similar (P > 0.05) between groups. Even if the decreasing rates of motility and membrane integrity were more rapid in presence of Equex than those in controls, total motility and sperm viability were similar at 3 and 6 h after thawing (P > 0.05). In Experiment 2, there was no difference in fertilizing ability and embryo development between the two groups (P > 0.05). The results of this study demonstrate that the addition of Equex STM Paste in the freezing extender avoids the loss of motile spermatozoa and maintains fertilizing ability of frozen-thawed spermatozoa.     

Effect of antioxidant supplementation in semen extenders on semen quality and reactive oxygen species of chilled canine spermatozoa

The objective of this study was to evaluate quality of chilled dog semen processed with extenders containing various antioxidants. Single ejaculates from five dogs were always pooled and evaluated for concentration, sperm motility, progressive motility (RSF-movement), viability, acrosomal integrity and by the hypo-osmotic swelling (HOS)-test. Also, superoxide (O(2)(-)) production, hydroxyl radicals (OH) and total reactive oxygen species (tROS) were determined. Pooled semen was divided in seven aliquots (for control and test conditions), which were diluted to a final concentration of 67x10(6)spermatozoa/ml with TRIS-glucose-egg yolk extender with or without the following supplements: control (without antioxidants), vitamin C (0.5mM), N-acetyl-l-cysteine (NAC; 0.5mM), taurine (0.2mM), catalase (100u/ml), vitamin E (0.1mM) and 5-(4-dimethylamino-phenyl)-2-phenyl-penta-2,4-dienoic acid (B16; 0.1mM). The semen aliquots were chilled and preserved at 4 degrees C. Portions of chilled semen were removed at 24 and 72h, and semen quality was evaluated after rewarming. At 24h the mean (+/-S.E.M.) sperm motility was higher (p<0.001) when vitamin E, taurine and B16 were added in the extender, whereas more spermatozoa with RSF-movement were observed (p<0.001) in the vitamin E, catalase, B16 and taurine groups. Sperm viability was higher (p=0.040) in B16 and vitamin E groups and the percentage of swollen spermatozoa was higher (p=0.002) only in the B16 group. Acrosomal integrity and OH were not significantly influenced by any of the antioxidants tested. Superoxide production was significantly lower when vitamin C, B16 and vitamin E were added in semen extenders compared with the control (p=0.017). All antioxidant groups, except vitamin C and NAC, contained less tROS compared to the control group, but only the B16 group value differed significantly (p=0.05). At 72h sperm motility was higher (p<0.001) when vitamin E, catalase, B16, taurine and NAC were added in the extender. More spermatozoa with RSF-movement were observed (p<0.001) in the vitamin E, catalase, B16, taurine and NAC treatment groups. Sperm viability was higher (p=0.001) when vitamin E, B16, taurine and vitamin C were added in semen extenders. HOS-test percentages were higher (p=0.016) in the B16, vitamin E, catalase and NAC groups. Acrosomal integrity was not influenced in any case. Production of O(2)(-) was significantly higher using catalase compared to all the other groups (p=0.006), while OH was not significantly influenced by any of the antioxidants tested. The addition of vitamin E, catalase and B16 in semen extenders resulted in significantly lower tROS values compared with the controls (p<0.0005). The results suggest that vitamin E and B16 had the most pronounced effect in preserving semen quality of chilled dog spermatozoa.     

Influence of centrifugation and different extenders on post-thaw sperm quality of ram semen

Using a 2-step extension methodology to freeze ram semen, 2 freezing protocols (P1 and P2) and 3 extenders were evaluated in a split-sample experiment. The freezing protocols were tested in combination with Extenders A and B (Experiment 1), and B and C (Experiment 2). Protocol 1 included centrifugation before filling the straws to reconcentrate the diluted semen to a calculated sperm concentration of 800 x 10(6) cells/mL. Protocol 2 involved appropriate ejaculate extension to yield 800 x 10(6) cells/mL as in P1, albeit avoiding centrifugation. Extenders A and B were milk-based and were supplemented with 5% egg yolk and fructose. Extender B was clarified by centrifugation (twice at 3310 g/20 min). Extender C was based on TRIS-citrate-fructose supplemented with 20% egg yolk and clarified as described for Extender B. Final glycerol concentration was 7% for all 3 extenders. Post-thaw parameters studied were subjective motility, computer assisted sperm motility analysis (CASA), membrane integrity (SYBR-14/P1), and capacitation status (chlortetracycline assay, CTC). The overall sperm concentration (x 10(6)/straw) differed (P<0.001) between P1 (mean+/-SD, 138.1+/-14.8) and P2 (216.5+/-13.9). Despite centrifugation, P1 appeared to be less harmful for spermatozoa than P2, yielding higher percentages of subjective motility, linearity, membrane integrity and uncapacitated spermatozoa. Due to the difference in concentrations obtained between P1 and P2, the total calculated numbers of spermatozoa having desirable characteristics were higher in samples processed as P2. In Experiment 1, P1 resulted in lower calculated numbers x 10(6) in the Aldose of subjective motility (87.2+/-5.1 vs 125.3+/-5.1; P<0.05), linearity (70.6+/-4.3 vs 79.8+/-4.3; NS), intact-membrane (77.4+/-5 vs 108.5+/-5.1; P<0.001), and uncapacitated (36.5+/-2.5 vs 46.5+/-2.5; P<0.05) spermatozoa, than P2. In Experiment 2, calculated sperm numbers (x 10(6)/straw) were lower in P1 than in P2 for subjective motility (80.8+/-5.4 vs 92.0+/-5.4; NS), linearity (63.3+/-5.6 vs 73.1+/-5.6; NS), membrane integrity (77.7+/-3.6 vs 101.0+/-3.6; P<0.001), and uncapacitated spermatozoa (28.3+/-3.24 vs. 4.1+/-3.2; P<0.01). Extender B (clarified milk extender) was consistently better than Extender A (nonclarified milk extender) for all parameters studied, but the difference was only statistically significant for linearity after 1 h of incubation at 38 degrees C (44.0+/-2.4 vs 36.2+/-2.4; P<0.05). Extender B was also better than Extender C (TRIS-citrate-fructose) for percentage of uncapacitated (49.7+/-2.2 vs 34.4+/-2.3; P<0.001), subjective motile (57.5+/-2.7 vs 43.8+/-2.7; P<0.01), and linear motile (46.5+/-2.8 vs 33.7+/-2.8; P<0.01) spermatozoa, but not for membrane integrity (51.6+/-1.5 vs 51.7+/-1.5). It was concluded that exclusion of centrifugation, as in P2, yielded higher sperm numbers with desirable characteristics per straw. Clarification of milk-based extender (B) resulted in better post-thaw sperm quality, especially compared with TRIS-based extender (C).     

Comparing sugar type supplementation for cryopreservation of boar semen in egg yolk based extender

Cryopreservation of boar semen is still considered suboptimal due to lower fertility when compared to fresh semen. The aim of this study was to evaluate the effects of the addition of different sugars (lactose, trehalose and glucose) on boar spermatozoa cryopreserved in an egg yolk based extender. Ejaculates were collected from a boar previously selected and semen samples were processed using the straw freezing procedure. In experiment 1, subsamples of semen were frozen in three different extenders: recommended lactose egg yolk extender (LEY); trehalose egg yolk extender (TEY) and glucose egg yolk extender (GEY). Sperm quality was assessed for motility, viability, acrosome integrity and hypoosmotic swelling test response upon collection, after freezing and thawing and then every hour for 3 h. Results showed that total motility at 1 and 3 h, progressive motility at 3 h, positive hypoosmotic response at 2 and 3 h and acrosome integrity at all times were significantly improved when trehalose was added to the extender. In experiment 2, sugar influence was also demonstrated in vitro fertilization. A total of 1691 oocytes were in vitro matured and inseminated with frozen-thawed sperm at 2000:1 sperm:oocyte ratio and coincubated for 6 h. Presumptive zygotes were cultured in NCSU-23 medium to assess fertilization parameters and embryo development. Both penetration and monospermy rates were significantly higher for trehalose frozen semen. A significant increase was observed in efficiency and blastocyst formation rates from TEY to the other groups. Our results demonstrated that trehalose extender enhances spermatozoa viability and its in vitro fertilization parameters in boar ejaculates with good sperm freezability. Further studies are necessary to assess the impact of sugars on the entire population.     

Sperm Viability in Ram Semen Diluted and Stored in Three Different Extenders

Semen was collected with an artificial vagina from 4 one-year-old rams, in order to study the changes in sperm motility and membrane integrity of spermatozoa split-diluted and stored at 5 °C during 7 days in sodium citrate, Tris, and milk-based extenders, respectively. Sperm motility was assessed subjectively and sperm membrane integrity was determined using the fluorescent probes Calcein-AM and Ethidium homodimer. Representative samples were studied using scanning electron microscopy (SEM). The average incidence of sperm motility decreased over time in all the extenders (p<.001). The incidence of spermatozoa showing progressive motility and intact plasma membrane was significantly higher in semen diluted with sodium citrate than in the other 2 extenders following 4 days of dilution until the end of the study. Evaluation with SEM confirmed the findings obtained with the supra vital fluorescent dyes. The results of the present study indicated that there were no differences between sodium citrate-, Tris- or milk-based extenders when ovine liquid semen was stored at 5 °C during a short period (2 days). However, when semen was stored for longer time, spermatozoa in the sodium citrate-based extender sustained its viability better.     

Effect of low density lipoproteins in extender on freezability and fertility of buffalo (Bubalus bubalis) bull semen

This study was designed to determine whether low-density lipoporoteins (LDLs) extracted from egg yolk in extender improve the freezability and fertility of buffalo bull semen. Semen from three Nili-Ravi buffalo bulls was diluted at 37 °C with tris-citric acid extender (50 × 10⁶ motile spermatozoa mL⁻¹) containing LDLs 2.5%, 5%, 10%, and 15% extracted from egg yolk and extender containing 20% egg yolk was kept as control. Diluted semen was cooled to 4 °C in 2 h, equilibrated at 4 °C for 4 h, filled in 0.5 mL French straws, and kept on liquid nitrogen vapors for 10 min. Straws were then plunged and stored in liquid nitrogen (-196 °C). Sperm motility (visually; %), plasma membrane integrity (%; with supravital hypo-osmotic swelling test), and viability (%; with dual staining test using Trypan-blue Giemsa) were assessed at post-dilution, pre-freezing and post-thawing. At post-dilution and pre-freezing, sperm progressive motility, plasma membrane integrity and viability was similar (P > 0.05) in extender containing 10% LDLs or the control. However, at post-thaw the aforementioned parameters were higher (P < 0.05) in extender containing 10% LDLs compared with the control and other experimental extenders. The fertility rate of inseminations performed were higher (P < 0.05) with extender containing 10% LDLs than the control. It was concluded that LDLs (10%) in extender improved the freezability and fertility of buffalo bull spermatozoa.     

Effect of different procedures of ejaculate collection, extenders and packages on DNA integrity of boar spermatozoa following freezing-thawing

Whole ejaculate or sperm-rich fraction, collected from four sexually mature boars, was frozen in an extender containing lactose-hen egg yolk with glycerol (lactose-HEY-G) or extender containing lactose, lyophilized lipoprotein fractions isolated from ostrich egg yolk and glycerol (lactose-LPFo-G), and Orvus Es Paste, respectively. The sperm samples were also frozen in a standard boar semen extender (Kortowo-3), without the addition of cryoprotective substances. Sperm DNA integrity was assessed using a modified neutral comet assay. Sperm characteristics such as motility, plasma membrane integrity (SYBR-14/PI), mitochondrial function (rhodamine 123) and acrosome integrity were monitored. Freezing-thawing caused a significant increase (P<0.05) in sperm DNA fragmentation, irrespective of the procedures of ejaculate collection and extender type. Sperm DNA fragmentation was significantly lower (P<0.05) in the whole ejaculate compared with the sperm-rich fraction, indicating that spermatozoa maintained in the whole seminal plasma prior to its removal for freezing-thawing procedure were less vulnerable to cryo-induced DNA fragmentation. Furthermore, spermatozoa frozen in lactose-HEY-G or lactose-LPFo-G extender exhibited lower (P<0.05) DNA fragmentation than those frozen in the absence of cryoprotective substances. The levels of sperm DNA damage, as expressed by comet tail length and tail moment values, were significantly higher (P<0.05) in sperm samples frozen in the absence of cryoprotective substances. The deterioration in post-thaw sperm DNA integrity was concurrent with reduced sperm characteristics. It can be suggested that evaluation of DNA integrity, coupled with different sperm characteristics such as motility, plasma membrane integrity and mitochondrial function, may aid in determining the quality of frozen-thawed boar semen.