Temperatures from 4 to 15 °C are suitable for preserving the fertilizing capacity of stallion semen stored for 22 h or more in INRA96 extender

Reimagining stallion sperm conservation: Combating carbotoxicity through pyruvate-induced Warburg effect to enhance sperm longevity and function

Although stallion spermatozoa are now recognized as highly dependent on oxidative phosphorylation for ATP production in the mitochondria, most extenders in use contain supraphysiological concentrations of glucose as the main energy source. While the toxicity of cryoprotectants has been well documented in the literature, the potential toxicity of excessive glucose in extenders is largely ignored. However, the toxicity of excess glucose, known as "carbotoxicity", is well-established in many areas of medicine. In this paper, we review the basic aspects of stallion spermatozoa metabolism, focusing on factors that significantly impact the lifespan and functionality of spermatozoa during conservation.

Effect of storage and single layer centrifugation before cryopreservation on stallion sperm cryosurvival

The objectives of this study were to evaluate the effect of a short, cooled storage before cryopreservation on sperm progressive motility (PM) and compare the effect of different centrifugation methods on post-thaw PM of stored samples. Semen was diluted in chilling extender and aliquoted in 6 protocols: i) Standard centrifugation (SC) followed by freezing; ii) Single Layer Centrifugation (SLC) followed by freezing; iii) Storage for 8 h/5 °C before SC; iv) Storage for 8 h/5 °C before SLC; v) Storage for 8 h/15 °C before SC; and vi) Storage for 8 h/15 °C before SLC. PM was assessed before centrifugation, after centrifugation, and post-thawing. Stallions were classified as "good freezers" (GF) or "bad freezers" (BF). The PM in samples immediately frozen was greater than in the stored ones (71.98 ± 14.2, 52.91 ± 17.8, 53.93 ± 18.9 for no storage, 5 ºC storage and 15 ºC storage, respectively) (P˂ 0.0001). There was an effect of storage condition (p ˂ 0.0001), centrifugation method (p ˂ 0.0001), and freezability (P=0.0016), with an interaction between them (P= 0.0004), on PM after centrifugation. Post-thaw PM was greater in samples treated by SLC than in samples processed by SC, for all storage conditions (p ˂ 0.05). All BF stallions 'showed post-thaw PM ˂ 30 % when samples were previously stored. Storage at 5 ºC or 15º C for 8 h maintains an appropriate quality in GF stallions. Applying a sperm selection technique as SLC is suggested to improve post-thaw motility, allowing GF straws to be frozen after storage, although BF semen should be prepared by SLC immediately after collection.

Validation of Calcein Violet as a New Marker of Semen Membrane Integrity in Domestic Animals

Many fluorochromes routinely used in semen quality analysis emit in the green and red channels, limiting their possible combination for multiple parameter analysis. The use of fluorophores emitting in different light channels broadens the possibilities of combination to expand the range of simultaneously evaluated criteria. This is of great interest in cases of small ejaculated volumes, such as those naturally occurring in roosters, small dog breeds and drones (Apis mellifera). The purpose of this experiment is to establish Calcein Violet (CaV), a blue fluorochrome, as a marker of viability and acrosomal integrity in domestic animals in order to free the red and green channels. SYBR®14/Propidium Iodide (PI) was used as reference dye, heat-treated samples as negative controls, serial staining combination for validation and epifluorescence microscopy for observation. Dead spermatozoa marked in red with PI showed no blue fluorescence either from the head or the tail. Live spermatozoa showed a decreasing blue emission from head to tail when single stained with CaV. Unreacted acrosomes showed intense blue fluorescence irrespective of plasma membrane integrity. This needs to be further confirmed for species with small and difficult to observe heads. Establishment of CaV as a marker of membrane integrity by fluorescence microscopy is a decisive first step towards further technical development and use with flow cytometry.

Effects of Extenders Supplementation with Gum Arabic and Antioxidants on Ram Spermatozoa Quality after Cryopreservation

Semen cryopreservation is very important in animal agriculture to maximize the number of daughters of genetically superior males and to distribute the cryopreserved semen of good males all over the world. However, the freezing process generates some damage to sperm that reduce their fertilizing ability after thawing. Moreover, egg yolk, which is the most common animal-origin cryoprotectant used in semen dilution, is considered a source of biosecurity risk. In the current study, we aimed to compare the replacement of egg yolk in the extender by gum arabic (5%) along with supplementation with antioxidant cysteine or ascorbic acid on semen quality and freezability in Noemi rams in vitro. Semen from six rams were collected with an artificial vagina two times per week. Semen evaluation parameters such as color, volume, pH, general motility, percentage motility, concentration and cell viability ratio were assessed. Spermatozoa motility and concentration were estimated with the computer-assisted semen analysis system. The semen samples were frozen using a Tris extender containing either 15% egg yolk or 5% gum arabic. For antioxidant-supplemented extenders, cysteine or ascorbic acid was dissolved at concentrations of 0.10, 0.50 or 1.0 mM in egg yolk or gum arabic extender. The semen from each ejaculate of each ram were resuspended with a specific extender with glycerol (5%); the final volume after dilution was 1 mL semen to 4 mL extender. The samples were then cooled to 4 °C for 120 min, loaded into 0.5 mL straws and frozen in liquid nitrogen for 7 days. Supplementation of gum arabic or egg yolk extenders for ram semen with antioxidants such as cysteine or ascorbic acid has beneficial effects on semen quality after cold storage or cryopreservation. However, supplementation of a 5% gum arabic extender with cysteine at 0.5 or 1 mM concentration or ascorbic acid at 0.5 mM concentration improved the quality of spermatozoa postcryopreservation. It could be concluded that gum arabic is a good alternative for egg yolk in Noemi ram semen extenders. Antioxidants are necessary to support the addition of gum arabic to the extender to help the ram spermatozoa to survive freezing-thawing and oxidative stresses.

Cooled storage of semen from livestock animals (part I): boar, bull, and stallion

This review is part of the Festschrift in honor of Dr. Duane Garner and provides an overview of current techniques for cooled storage of semen from livestock animals. The first part describes the current state of the art of liquid semen preservation in boars, bulls, and stallions, including the diluents, use of additives, processing, temperature, and cooling of semen. The species-specific physiology and varying extents of cold shock sensitivity are taken into consideration. In addition, factors influencing the quality of cooled-stored semen are discussed. Methods, trends, and the most recent advances for improving sperm quality during cold-temperature storage are highlighted and their respective advantages and disadvantages are contrasted. There has been much progress in recent years regarding cold-temperature storage of boar sperm and there is great potential for a large-scale use to replace the current 17 °C temperature storage regime and the associated use of antibiotics in the future. For stallion sperm, there is an opposite trend away from previous low-temperature storage towards storage at higher temperatures to increase sperm viability and longevity. In bulls, liquid storage of sperm is mostly used in the seasonal dairy production systems of New Zealand and Ireland, but with further research focusing on shelf-live elongation of liquid preserved sperm, there is potential for an application in breeding programs worldwide.

The efficiency of different types of extenders for semen cooling in stallions

Objective

This study was focused on the influence of the skimmed milk-based extender (SM), the INRA 96 extender and BotuSemen Gold extender on parameters of stallions' ejaculate during storage.

Methods

In this study, 14 stallions between 4 and 20 years of age were monitored. Total and progressive motility, viability and morphology of sperm were evaluated at time intervals of 24, 48 and 72 hours after collection.

Results

The total motility, progressive motility, and values of sperm with normal morphology were significantly higher in the INRA 96 and BotuSemen Gold extenders than in the skimmed milk-based extender (p < 0.01). The sperm viability differed significantly in all extenders (p < 0.01). The highest value of sperm viability was in INRA 96 (64.69 ± 0.67%) and lowest in skimmed milk-based extender (59.70 ± 0.81%). The highest differences occurred at 72 hours of storage. Values of total motility, progressive motility and sperm viability decreased over time (p < 0.01). In case of sperm morphology there was no statistically significant decrease between 48- and 72-hour time intervals.

Conclusion

It can be concluded that the extenders with a chemically defined composition have shown better indicators of insemination capabilities in ejaculates than the skimmed milk-based extender. The BotuSemen Gold extender is a suitable alternative to the INRA 96, when used within 48 hours; after 72 hours of storage, however, the INRA 96 showed a higher share of viable spermatozoa.

INRA96 Supplemented With Phospholipids Liposomes, A Promising Approach for Stallion Sperm Chilling

Among biotechnologies of reproduction in the equine species, artificial insemination remains the most used technology especially for cooled transported sperm. Although the use of INRA96 extender has demonstrated its efficiency for long-term sperm storage at 4°C or 15°C, some stallions ("bad coolers") are excluded from such technology. Some years ago, we demonstrated that liposomes produced from egg yolk (EY) phospholipids could be an alternative to egg yolk plasma in stallion freezing extenders. To develop a new extender for sperm chilling, we evaluated the protective effect of liposomes produced from EY phospholipids on stallion sperm storage at 4°C. The sperm of stallions from two studs was diluted in INRA96 extender (as control) or an experimental extender (EE) composed of INRA96 supplemented with liposomes of EY phospholipids. After 24H (D1), 72H (D3), and 6 days (D6) or 7 days (D7), motility parameters were evaluated using Computer Assisted Semen Analyzer. Our results demonstrated that total and progressive motility decreased significantly after dilution and storage in INRA96 between D1 and D3 (P < .05) while no significant decrease was observed between D1 and D3 with EE. Regarding VAP parameter, no significant difference was observed between extenders except at D7 in stud 2. Moreover, total and progressive motility were maintained at a significantly higher level (D3, D6, D7) when sperm was stored in EE compared to INRA96. These promising results demonstrate that the supplementation of INRA96 extender with egg-yolk phospholipids liposomes allows a higher protection to stallion sperm cells.

Motility and Fertility Evaluation of Thawed Frozen Stallion Semen After 24 Hours of Cooled Storage

Breeding mares with cryopreserved semen requires specialized equipment for storage and thawing and more intensive mare management. The objectives of this study were (1) evaluate the longevity of frozen stallion semen once it had been thawed, extended, and maintained at 5°C for 48 hours in a passive cooling container, and (2) determine fertility potential of frozen semen that had been thawed, extended, and used to inseminate mares after 24 hours of cooled storage. Eight ejaculates were collected and aliquots were cooled in either INRA96 and CryoMax LE minus cryoprotectant at a concentration of 50 million total sperm/mL. The remainder of the ejaculate was frozen in CryoMax LE extender at a concentration of 200 million total sperm/mL. Semen was thawed using 1 of 3 thawing protocols, and diluted to a concentration of 50 million total sperm/mL in either INRA96 or CryoMax LE minus cryoprotectant and cooled to 5°C. Sperm motility was evaluated at 24 and 48 hours. Eight mares were inseminated over two estrous cycles using frozen semen that had been thawed, extended in INRA96, and cooled for 24 hours. There was no difference in progressive motility at 24 or 48 hours of cooled-storage post-thaw between the 3 thawing protocols. An overall per cycle pregnancy rate of 56% (9/16 cycles) was achieved using frozen-thawed semen that had been extended and cooled for 24 hours. In summary, frozen stallion sperm was thawed, extended, and cooled to 5°C for 24 hours and still maintained adequate (>30%) sperm motility and fertility.

Effects of glucose concentration in semen extender and storage temperature on stallion sperm quality following long-term cooled storage

In Experiment 1, the effects of glucose concentration in extender (0 mM, 67 mM, 147 mM, 270 mM; G0, G67, G147, and G270, respectively) and storage temperature of extended semen (5, 10, 15 and 20 °C) were evaluated after storage for up to 5 days (T0h to T120h). For all time points tested, mean total (TMOT) and progressive (PMOT) sperm motility were lower in G0 than all other treatment groups (P < 0.05). Mean curvilinear velocity (VCL) was lower in G0 than other treatment groups at all time points tested except T0h (P < 0.05). Mean percentage of plasma membrane/acrosome intact sperm (VAI) was similar among treatments at T0h, T72h, and T120h (P > 0.05). Mean TMOT and PMOT, were lower for semen stored at 20 °C than all lower storage temperatures (P < 0.05) at all time points. In Experiment 2, semen was stored at 10 °C in extender containing no added glucose (G0) or 147 mM glucose (G147). Following storage, semen was centrifuged and resuspended in extender containing no added glucose (G0 - G0 or G147 - G0, respectively) or 147 mM of glucose (G0 - G147 or G147 - G147, respectively). Mean TMOT, PMOT, and VCL were higher in G147 than G0 at all time periods tested (P < 0.05), whereas mean VAI was similar between these treatment groups throughout the experiment (P > 0.05). Mean TMOT and PMOT were higher in G0 - G147 than G0 - G0 at T72h and T120h (P < 0.05) and mean VCL was higher in G0 - G147 than G0 - G0 for all time periods. Mean TMOT, PMOT, and VCL were higher in G147 - G147 than G147 - G0 at all time points tested (P < 0.05), whereas mean VAI was similar between these two treatment groups for each of the time points (P > 0.05). In Experiment 3, the minimum concentration of glucose required to maintain sperm quality following long-term cooled storage (T120 h) was evaluated (G0, G5, G10, G20, G40, G67, G147 mM). At T120 h, mean TMOT was lowest in G0, G5, G10, and G20 (P < 0.05), whereas mean PMOT and VCL were lower in G0, G5, G10, and G20 than in G40, G67, and G147 (P < 0.05). Mean VAI was higher in G10 than G67, but similar among G10 and other treatment groups (P > 0.05). In conclusion, the absence of added glucose in extender reduced the motion characteristics of stallion sperm during long-term storage (5 days), but VAI was not affected. The use of temperatures between 5 and 15 °C for long-term storage (5 days) best maintained sperm motility and VAI. The threshold concentration of added glucose in extender required to optimize sperm motion characteristics was 40 mM.

Short-term tolerance of equine spermatozoa to various abiotic factors

The aim of this study was to determine the effects of various abiotic factors, such as light, physical stress (pipetting) and thermal shock, on the quality of fresh and cooled equine sperm. In experiment I, four sperm aliquots were subjected to different light exposures: (i) protected control samples (CTRL), (ii) exposed to UV light at 10 cm (UV10), (iii) exposed to UV light at 20 cm (UV20) and (iv) exposed to laboratory lighting (LAB). In experiment II, four semen aliquots were subjected to repeated pipetting for 0, 10, 20 and 30 times (CTRL, P10, P20 and P30, respectively). In experiment III, four semen aliquots at 15°C were subjected to thermal oscillations: (i) cooled control sperm at 15°C (CTRL), (ii) oscillations of 1.9°C/min to a temperature of 30°C (T30), (iii) oscillations of 1.4°C/min, with the temperature rapidly falling until reaching 1.3°C (T0R) and (iv) oscillations of 1.1°C/min, with the temperature slowly falling until reaching 4.2°C (T0S). The results revealed that after 30 min, UV10 and UV20 sperm samples showed significantly (p < .05) lower total and progressive motility values, sperm kinematic parameters and mitochondrial potential. After 45 min of exposure, differences were highly significant (p < .001). No significant differences (p > .05) were found for pipetting or thermal oscillations. The results suggest that, even if equine sperm samples are not handled in the laboratory under optimal conditions, fresh and cooled equine spermatozoa are able to resist the impact of various abiotic stimuli without any reduction in their quality. This study analyses the effect on normospermic samples, but future research could look at the tolerance that asthenozoospermic equine samples have to these abiotic influences.

Development of a new fertility prediction model for stallion semen, including flow cytometry

Several laboratories routinely use flow cytometry to evaluate stallion semen quality. However, objective and practical tools for the on-field interpretation of data concerning fertilizing potential are scarce. A panel of nine tests, evaluating a large number of compartments or functions of the spermatozoa: motility, morphology, viability, mitochondrial activity, oxidation level, acrosome integrity, DNA integrity, "organization" of the plasma membrane, and hypoosmotic resistance, was applied to a population of 43 stallions, 33 of which showing widely differing fertilities (19%-84% pregnancy rate per cycle [PRC]). Analyses were performed either within 2 hours after semen collection or after 24-hour storage at 4 °C in INRA96 extender, on three to six ejaculates for each stallion. The aim was to provide data on the distribution of values among said population, showing within-stallion and between-stallion variability, and to determine whether appropriate combinations of tests could evaluate the fertilizing potential of each stallion. Within-stallion repeatability, defined as intrastallion correlation (r = between-stallion variance/total variance) ranged between 0.29 and 0.84 for "conventional" variables (viability, morphology, and motility), and between 0.15 and 0.81 for "cytometric" variables. Those data suggested that analyzing six ejaculates would be adequate to characterize a stallion. For most variables, except those related to DNA integrity and some motility variables, results differed significantly between immediately performed analyses and analyses performed after 24 hours at 4 °C. Two "best-fit" combinations of variables were determined. Factorial discriminant analysis using a first combination of seven variables, including the polarization of mitochondria, acrosome integrity, DNA integrity, and hypoosmotic resistance, permitted exact determination of the fertility group for each stallion: fertile, that is, PRC higher than 55%; intermediate, that is, 45% < PRC less than 55%; or subfertile, that is, PRC less than 45%. Linear regression using another combination of 20 variables, including motility, viability, oxidation level, acrosome integrity, DNA integrity, and hypoosmotic resistance, accounted for 94.2% of the variability regarding fertility and was used to calculate a prediction of the PRC with a mean standard deviation of 3.1. The difference between the observed fertility and the calculated value ranged from -4.2 to 5.0. In conclusion, this study enabled to determine a new protocol for the evaluation of stallion semen, combining microscopical observation, computer-assisted motility analysis and flow cytometry, and providing a high level of fertility prediction.

A comparative study of two cooling protocols on stallion sperm cryosurvival

There are many protocols for horse sperm cryopreservation, but results are inconsistent; sperm survival after freeze-thawing is usually poor; in consequence, fertility is low. The objective of this work was to see whether slow cooling before freezing to minus 3 °C instead of +5 °C, the traditional target temperature, could improve horse sperm cryosurvival, capability to carry out capacitation and the acrosome reaction induced by progesterone. Spermatozoa from five stallions were packaged in straws and slowly cooled to +5 °C. Half of the straws were frozen directly and the other half was further cooled to -3 °C before freezing. Progressive motility, viability, plasma membrane integrity, acrosome integrity and capacitation status were assessed. After thawing, there were no differences between cooling treatments on motility, viability, acrosome integrity and capacitation status; however, there was difference (P < 0.05) regarding plasma membrane integrity. Acrosome integrity decreased as incubation, without or with progesterone (2 μg ml(-1) ), progressed, but there were no differences between cooling treatments regardless of progesterone. Both capacitated and acrosome-reacted spermatozoa increased as incubation progressed, but there were no differences between cooling treatments regardless of progesterone. Slow cooling to -3 °C before freezing did not improve horse sperm cryosurvival or capability to undergo the acrosome reaction.

L-carnitine and pyruvate are prosurvival factors during the storage of stallion spermatozoa at room temperature

The spermatozoa of many stallions do not tolerate being cooled, restricting the commercial viability of these animals and necessitating the development of a chemically defined room temperature (RT) storage medium. This study examined the impact of two major modulators of oxidative phosphorylation, pyruvate (Pyr) and L-carnitine (L-C), on the storage of stallion spermatozoa at RT. Optimal concentrations of Pyr (10 mM) and L-C (50 mM) were first identified and these concentrations were then used to investigate the effects of these compounds on sperm functionality and oxidative stress at RT. Mitochondrial and cytosolic reactive oxygen species, along with lipid peroxidation, were all significantly suppressed by the addition of L-C (48 h MitoSOX Red negative: 46.2% vs. 26.1%; 48 and 72 h dihydroethidium negative: 61.6% vs. 43.1% and 64.4% vs. 46.9%, respectively; 48 and 72 h 4-hydroxynonenal negative: 37.1% vs. 23.8% and 41.6% vs. 25.7%, respectively), while the Pyr + L-C combination resulted in significantly higher motility compared to the control at 72 h (total motility: 64.2% vs. 39.4%; progressive motility: 34.2% vs. 15.2%). In addition, supplementation with L-C significantly reduced oxidative DNA damage at 72 h (9.0% vs. 15.6%). To investigate the effects of L-C as an osmolyte, comparisons were made between media that were osmotically balanced with NaCl, choline chloride, or L-C. This analysis demonstrated that spermatozoa stored in the L-C balanced medium had significantly higher total motility (55.0% vs. 39.0%), rapid motility (44.0% vs. 25.7%), and ATP levels (70.9 vs. 12.8 ng/ml) following storage compared with the NaCl treatment, while choline chloride did not significantly improve these parameters compared to the control. Finally, mass spectrometry was used to demonstrate that a combination of Pyr and L-C produced significantly higher acetyl-L-carnitine production than any other treatment (6.7 pg/10(6) spermatozoa vs. control at 4.0 pg/10(6) spermatozoa). These findings suggest that Pyr and L-C could form the basis of a novel, effective RT storage medium for equine spermatozoa.