Cryopreservation of stallion semen has not reached the level of efficiency and positive results described in other species. This is mainly due to the greater sensitivity of stallion sperm to the freezing process, showing higher rates of oxidative stress and plasma membrane damage, which trigger the activation of several cell damage pathways that ultimately culminate in DNA fragmentation and cell death. Therefore, finding molecules that improve the efficiency of this technique in stallion by preventing oxidative stress and cell damage is required. Thus, the aim of the present study was to evaluate the effect of adding three antioxidants (MnTBAP, NAC and FeTPPS) to the freezing medium on the quality and functional parameters of stallion sperm. Semen samples from three stallions frozen with the antioxidants were evaluated in two conditions: (a) adding the antioxidants before freezing, and (b) before and after freezing. Plasma membrane integrity, mitochondrial membrane potential, lipid peroxidation, intracellular ROS levels, membrane lipid disorder, DNA damage, sperm motility and binding to the zona pellucida were assessed. The results showed that MnTBAP was the antioxidant treatment that best controlled the oxidative stress process and post‐thaw cell damage, showing higher plasma membrane integrity, mitochondrial membrane potential, sperm motility, number of spermatozoa bound to the zona pellucida of bovine oocytes and lower lipid disorder. Additionally, it was determined that a second post‐thaw application of antioxidants is detrimental since induced higher cell damage and lower sperm motility, without showing any beneficial effect on the spermatozoa.

Conventional in vitro fertilization has not yet been implemented in the equine species. One of the main reasons has been the inability to develop a culture medium and incubation conditions supporting high levels of stallion sperm capacitation and hyperactivation in vitro. Although different culture media have been used for this purpose, human tubal fluid (HTF) medium, widely used in the manipulation of human and mice gametes, has not been reported so far in stallion sperm culture. The first part of this study aimed to compare HTF and Whitten's media on different stallion sperm quality and capacitation variables. Additionally, the effect of procaine, aminopyridine and caffeine in both media was evaluated on sperm motility parameters at different incubation times. Integrity and destabilization of the plasma membrane were evaluated by merocyanine 540/SYTOX Green (MC540), mitochondrial membrane potential (∆Ψm) using tetramethylrhodamine methyl ester perchlorate (TMRM), acrosome membrane integrity by PNA/FITC and tyrosine phosphorylation by P-tyrosine mouse mAb conjugated to Alexa Fluor® by flow cytometry. Motility parameters were evaluated using the integrated semen analysis system (ISAS®). We found no differences between Whitten's and HTF media and incubation time in terms of sperm viability, uninduced acrosome membrane damage or mitochondrial membrane potential at 30- and 120-min incubation. Membrane fluidity (MC540) increased in both media at 30- and 120-min incubation compared to noncapacitating conditions. Similarly, tyrosine phosphorylation increased in both media in capacitating conditions at 2- and 4-hr incubation compared to noncapacitating conditions. Although procaine showed the best result in terms of sperm hyperactivated motility in both media, aminopyridine also showed parameters consistent with the hyperactivation including an increase in curvilinear velocity and decrease in straightness. In conclusion, HTF medium and aminopyridine equally support capacitation-related parameters in stallion sperm.

RESUMEN:Los procedimientos de criopreservación inducen cambios morfofuncionales en los espermatozoides. Es importante post descongelación espermática utilizar procedimientos de selección que permitan recuperar espermatozoides altamente funcionales. El objetivo del presente estudio fue comparar la eficiencia del Swim-up y Equipure® en la selección de espermatozoides funcionales en semen descongelado de equino. Semen de 4 potros reproductores Criollos Chilenos (A, B, C y D), fueron descongelados separadamente y procesados (n=15) por: I.-Swim-up (SU) y II.-Equipure® (EQ). Post descongelación se determinó por citometría de flujo la viabilidad e integridad de membrana plasmática (SYBR-14/PI), potencial de membrana mitocondrial (Ψ∆m; JC-1), integridad de la membrana acrosomal (FITC-PSA/PI). La motilidad progresiva (%) en dos animales fue más alta (P<0,05) por SU comparado con EQ: A (55,7±5,8% v/s 38,17±3,7%) y C (37,5±7% vs. 32±2,1%, respectivamente). La integridad de la membrana plasmática (%), tres animales presentaron diferencias (P<0,05), siendo más alta por SU en dos animales comparado con EQ (A: 54,3±1,7 vs. 36,7±1,9, C: 36,1±5,7 vs. 29,4±4,8 y D: 34,4±9,4 vs. 52,7±5,2; respectivamente), solamente un animal fue superior EQ. En el Ψ∆m (%), diferencias significativas (P<0,05) fueron detectadas en los cuatro animales, siendo más altos en SU comparado con EQ (A: 69,1±8,6% vs. 47,4±3,3%, B: 59,34±12,3% vs. 24,8±1,5%, C: 54,9±12,3% vs. 43,2±3,1% y D: 53,1±17,6% vs. 37,5±5,7%; respectivamente). Los resultados obtenidos en el presente estudio demostraron que los métodos de selección espermática Swim-up y Equipure® permiten recuperar espermatozoides de diferente calidad funcional en semen congelado-descongelado de equino, presentándose diferencias individuales entre los animales con respecto a los métodos. Se observó una tendencia del método Swim-up en seleccionar espermatozoides de equino descongelados con mayor calidad funcional comparado con Equipure®. PALABRAS CLAVE. Equino; Espermatozoide; Swim-up; Equipure® INTRODUCCIÓNLa aplicación de técnicas de asistencia reproductiva tales como inseminación artificial (IA) con semen congelado permiten aumentar el potencial reproductivo de los equinos (Pojprasath et al., 2011). La criopreservación de espermatozoides es de gran relevancia para la industria de reproducción equina, permitiendo el almacenamiento por períodos de tiempo prolongados y el transporte de semen a lugares distantes (Hoffmann et al., 2011) y utilizar a los potros simultáneamente en reproducción y en competición (Schober et al., 2007). A pesar de la creciente demanda comercial para utilizar semen congelado de equino, la tasa de preñez después de la IA es más baja comparadas con las obtenidas con semen fresco o refrigerado, e incluso inferiores a la obtenida en otras especies domésticas (López-Fernández et al., 2007). Es importante señalar que, existe un alto grado de variabilidad en la calidad del semen entre los machos e incluso entre los eyaculados de un mismo animal (Dowsett & Knott, 1996) como también en ...

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Conventional IVF has not yet been implemented in the equine species. One of the main reasons has been the inability to develop a culture medium and incubation conditions supporting high levels of stallion sperm capacitation and hyperactivation in vitro. Although different culture media have been used for this purpose, human tubal fluid (HTF) medium, widely used in the manipulation of human and mice gametes, has not been reported so far in stallion sperm culture. Thus, the first part of this study aimed to compare HTF (Summers and Biggers, 2003 Hum. Reprod. Update9, 557-582, DOI: 10.1093/humupd/dmg039) and Whitten’s (McPartlin et al. 2009 Biol. Reprod.81, 199-206, DOI: 10.1095/biolreprod.108.074880) media on different stallion sperm quality and capacitation variables. Additionally, the effect of procaine, aminopyridine and caffeine on sperm motility parameters was evaluated in both media at different incubation times. Fresh semen from 3 Chilote stallions was collected, diluted to 10×106 sperm mL−1 in capacitating (7mg mL−1 BSA and 25mM NaHCO3) and non-capacitating (without BSA and NaHCO3) HTF and Whitten’s media and incubated for 30 and 120min at 38°C in air atmosphere. Integrity and destabilisation of the plasma membrane were evaluated by merocyanine 540/SYTOX Green (MC540), mitochondrial membrane potential (ΔΨm) using tetramethylrhodamine methyl ester perchlorate, acrosome membrane integrity by peanut agglutinin/fluorescein isothiocyanate and tyrosine phosphorylation by P-tyrosine mouse mAb conjugated to Alexa Fluor® in a FACSCanto II flow cytometer (Becton, Dickinson and Co., Franklin Lakes, NJ, USA). A total of 10,000 sperm events were acquired from each measurement (n=3 replicates for each stallion). Motility parameters were evaluated using the integrated semen analysis system (ISAS®, Selinion Medical, Brussels, Belgium). Percentage data were arcsine transformed and subjected to a 2-way ANOVA with Bonferroni’s post hoc test using Prism 7 software (GraphPad Software, La Jolla, CA, USA). We found no differences between Whitten’s and HTF media in terms of sperm viability, uninduced acrosome membrane damage or mitochondrial membrane potential at 30 and 120min of incubation. Membrane fluidity (MC540) increased in both media at 30 and 120min of incubation compared with non-capacitating conditions. Similarly, tyrosine phosphorylation increased in both media in capacitating conditions at 2 and 4h of incubation compared with non-capacitating conditions, without differences between media. Although procaine showed the best result in terms of sperm hyperactivated motility in both media, aminopyridine also showed parameters consistent with hyperactivation including an increase in curvilinear velocity and decrease in straightness. In conclusion, HTF medium and aminopyridine equally support capacitation-related parameters in stallion sperm. Funding support was received from FONDECYT 1160467 CONICYT, Chile.