The HOS test and its relationship to fertility in the stallion

Comparison of different cryoprotectants for freezing donkey (Equus asinus) semen

The aim of this study was to evaluate two cryoprotectants, dimethylformamide (DMF) and methylformamide (MF) in two concentrations (5 and 7 %) in vitro in donkey semen using a rapid freezing technique and the effect on pregnancy rates in mares. Twenty-four ejaculates from 8 jacks (n = 8; r = 3) were divided into 4 extenders: BotuSemen Gold with 5 % or 7 % MF and 5 % or 7 % DMF, all containing 11 % lactose, 20 % egg-yolk and 0.5 % Equex. Post-thaw evaluations included: sperm motility, membrane function and acrosome status. A linear mixed effect model was used to test the effect of different freezing media on semen parameters. No differences were observed between the 4 freezing media used, for any of the seminal parameters (P > 0.05). However, samples with 5 % DMF showed the highest percentages of sperm with acrosomes and functional membranes (DMF: 5 %: 53.67 ± 22.01; 7 %: 33.92 ± 23.4; MF: 5 %: 44.5 ± 20.46; 7 %: 38.75 ± 27.4) (Data: mean ± SD; P > 0.05). Hence, thirty mares were inseminated: 15 with 5 % DMF and 15 with 7 % DMF. The pregnancy rate was 46 % (7/15) and 0 % (0/15) using the extender with 5 % or 7 % DMF, respectively (P = 0.003). To conclude, the use of 5 % or 7 % of MF or DMF did not affect the in vitro parameters. Despite the lack of differences in vitro with the two DMF concentrations, in vivo results only showed pregnancies when using 5 % DMF. Thus, the results of this study demonstrate the importance of accompanying in vitro semen evaluations with studies that evaluate post-insemination pregnancy rates.

Glass wool column filtration for stallion sperm selection: A comparative analysis with the single-layer colloid centrifugation

Glass wool column filtration (GWCF) selects human, bull, boar, dog and buffalo spermatozoa, but reports in the horse are scarce. Single-layer colloid centrifugation with Androcoll-E™ is currently the standard procedure to select good-quality equine sperm. This study was designed to assess GWCF (50 and 75 mg columns; GWCF-50 and GWCF-75, respectively) efficacy to select good-quality sperm from fresh and frozen-thawed equine semen, and to compare its performance with Androcoll-E™ colloid centrifugation. Percentage total motile (TM), progressively motile (PM), morphologically normal (MN), osmotically competent (HOS+) and acrosome-intact/osmotically competent (AI/HOS+) sperm were determined. In studies done with fresh semen samples (n = 17), suspensions subjected to GWCF-50 showed an improvement (p < .05) in PM and HOS+ sperm after selection. With GWCF-75, an increase (p < .05) in PM, MN and HOS+ sperm was observed. Results with GWCF were comparable or better than with Androcoll-E™ selection. Sperm recovery was similar between procedures for all semen parameters. Total sperm count recovery was lower after GWCF-75 (GWCF-50 = 60.0; GWCF-75 = 51.0; Androcoll-E™ = 76.0 million sperm; median; p = .013), but results on total progressive sperm count were similar (GWCF-50 = 23.0; GWCF-75 = 27.0; Androcoll-E™ = 24.0 million sperm; median; p = .3850). Using frozen-thawed semen samples (n = 16), an improvement (p < .05) in TM, PM, NM, HOS+ and AI/HOS+ sperm was observed in GWCF-75 filtrates. Results were comparable to Androcoll-E™ centrifugation, except HOS+ that increased (p < .05) only after GWCF-75. Recovery was comparable for all parameters in frozen samples. GWCF is a simple and low-cost procedure that selects equine sperm with a quality comparable to colloid centrifugation with Androcoll-E™.

Hypo-Osmotic Swelling Test (HOST) for Feline Spermatozoa: The Simplified Procedure and the Aspect of Sperm Morphology

Hypo-osmotic swelling test (HOST) is used to assess the functional integrity of sperm plasma membranes in many species. The primary aim of this study was to test a simplified HOST procedure for the evaluation of feline semen. The second objective was to check if sperm abnormalities can influence the results of this test. Urethral semen was collected from 19 male, domestic cats. In Exp. 1, HOST was performed in different media (50 mOsm/kg fructose or distilled water), temperature (37 °C or room temperature) and time (5 and 30 min). In Exp. 2, the potential effect of sperm abnormalities on HOST results was assessed by observing individual normal and abnormal spermatozoa microinjected into droplets of distilled water. The results showed no differences between the HOST results performed in different media, temperature and time. Viable abnormal spermatozoa were able to swell under hypo-osmotic conditions in the same manner as normal ones, except spermatozoa with distal droplets, which showed a higher frequency of ‘despiralization’. In conclusion, HOST can be reliably performed at 0 mOsm/kg for 5 min at room temperature, which may contribute to a wider use of this test under clinical environments. Viable abnormal spermatozoa are able to swell under hypo-osmotic conditions; therefore, their presence in the ejaculate would not bias the results of HOST when total coiling is calculated.

Characteristics of diluted-stored and post-thawed semen of Hutsul stallions

The use of frozen semen lowers the risk of disease transmission, eliminates geographical limitations and supports the implementation of genetic resource protection programs. However, due to the very rare use of frozen semen from Hutsul stallions, their genetic material is not secured in sperm banks, and very little information is available about their semen, including its suitability for cryopreservation, and sperm survival rates after thawing. The aim of this study was to analyse basic parameters such as sperm motility, vitality and morphology in diluted-stored and post-thawed Hutsul semen, using a CASA system. There were no differences in sperm motility (P = 0.3372) or morphology between the groups, although the progressive motility was higher in thawed semen (P = 0.0151), while the sperm vitality was higher in diluted-stored semen (P = 0.00517). This study demonstrates that semen from Hutsul horses is suitable for cryopreservation, thus supporting the creation of a sperm bank as a genetic reserve for representatives of this breed.

Effect of plasma separation techniques and sperm selection on sperm recovery and viability of cooled pony stallion semen for 48h at 5°C

ABSTRACT Separation techniques of seminal plasma [centrifugation (SC) and Sperm Filter® (SF)] and sperm selection [Androcoll-E (SCA) and filtration glass wool (GW)] were used in 24 ejaculates from 6 stallions. In experiment 1, the ejaculates were allocated into control (no spin), centrifugation at 600 g x 10min, SF and GW. In experiment 2, semen was submitted to SC, SGA and filtered through GW. Following the treatments in both experiments, samples were kept chilled at 5°C to 50 x 106 sperm/ml for 48h. The variables measured on fresh and cooling semen were pH, motility, membrane viability function by 6-carboxyfluorescein diacetate and propidium iodide (CFDA / PI), viability or vitality (eosin / nigrosine) and mitochondrial activity. In experiment 1, centrifugation to remove seminal plasma resulted in greater damage to sperm than separation by sperm filter, and selection by glass wool was more efficient in separating viable cells and maintaining viability during cooling. In experiment 2 Androcoll-E and glass wool treatments resulted in higher (P <0.0001) motility, membrane function, mitochondrial activity, and viability than centrifuged semen. Both selection by Androcoll- E and glass wool improved the quality of semen pony stallions for preservation for up to 48h to 5ºC.

Seasonal variations in quantitative and qualitative sperm characteristics in fertile and subfertile stallions

Horses are seasonal breeders with a natural breeding season beginning in spring and extending through midsummer. In this study, quantitative and qualitative parameters of chilled stallion semen were compared between fertile and subfertile stallions and between the breeding and the non-breeding season. Semen quality parameters compared included ejaculate volume, sperm concentration, total sperm number, sperm morphology, and computer-assisted semen analysis (CASA)-derived sperm movement characteristics obtained from two groups of warmblood stallions (n=8; four fertile stallions and four subfertile stallions), which differ in the seasonal pregnancy rate 80 %–90 % (fertile) vs. 40 %–60 % (subfertile). A total of 64 ejaculates were collected from the stallions (n=8; four in the breeding season and four in the non-breeding season of each stallion). No significant differences in the semen quality parameters between the fertile and the subfertile stallions in the non-breeding season were observed. However, in the breeding season the proportion of morphologically normal sperm, total motility, progressive motility, average path velocity (VAP), and curvilinear velocity (VCL) were significantly higher in the fertile group (P<0.05) when compared with the subfertile group. In addition, a significant seasonal variation in the proportion of morphological normal sperm was found in the fertile group between the breeding and the non-breeding season (P<0.05). Moreover, significant seasonal variations (P<0.05) in CASA parameters of mean VAP, straight line velocity (VSL), and beat-cross frequency (BCF) were observed in the fertile and the subfertile stallions, which tended to be lower in the non-breeding season. In conclusion, differences between the fertile and the subfertile stallions were observed only in the breeding season, and a few of CASA-derived parameters seemed to be significantly lower during the non-breeding season in both the fertile and the subfertile stallions.

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.

Características do sêmen a fresco e descongelado de garanhões da raça Nordestina

RESUMO: Este estudo descreveu as características seminais, da membrana plasmática e do acrossoma de espermatozoide congelado/descongelado de 19 ejaculados de garanhões da raça Nordestina. Os aspectos analisados incluíram os parâmetros físicos do sêmen fresco; a motilidade e a longevidade do sêmen diluído e descongelado; a morfologia espermática, integridade funcional e estrutural da membrana plasmática do espermatozoide e a habilidade de ligação do espermatozoide à membrana perivitelina da gema do ovo de galinha do sêmen descongelado. As variáveis foram avaliadas pela ANOVA com post hoc teste de Student Newman-Keuls (P<0,05). A MT e a MP foram maiores (P<0,05) no sêmen diluído do que no descongelado. A percentagem média de defeitos maiores, menores e totais foi muito inferior ao limite recomendado pelo CBRA. A porcentagem de reativos ao HOST foi de 14,21±1,12% e a porcentagem média de membranas íntegras detectadas pelo teste supravital de 62,22±9,06% e pela sonda SYBR-14 de 81,47±26,90. O número médio de espermatozoides ligados à MPV após a descongelação do sêmen foi de 230,39±57,09. A MT e MP no tempo 0 min do TTR foi superior (P<0,05) em relação a 150 min, não diferindo nos tempos 10 min e 30 min. Os resultados demonstram que a utilização dos testes laboratoriais adicionais ajudam no processo de avaliação das amostras, possibilitando a obtenção de informações mais confiáveis e precisas. Embora a criopreservação tenha provocado queda na motilidade seminal, o uso de diluidor contendo amidas minimizou os danos osmóticos nas células espermáticas e manteve a integridade morfológica, funcional e estrutural da membrana plasmática do espermatozoide. Estes resultados são um referencial em estudos futuros uma vez que, inexistem dados comparativos nesta raça.

Copy number differences of Y chromosomal genes between superior and inferior quality semen producing crossbred (Bos taurus × Bos indicus) bulls

The removal of crossbred bulls from semen collection programs due to the production of poor quality semen causes substantial monetary losses to the dairy industry. Seminal quality, a quantitative trait, is greatly influenced by genome level variations. Deletion and/or duplication of Y chromosomal genes and subsequent changes in gene copy number have a major role in determining spermatogenic efficiency and, therefore, seminal quality. In this study, copy numbers of three Y chromosomal genes TSPY, DDX3Y, and USP9Y in genomic DNA were estimated and compared in two groups of crossbred (Bos taurus × Bos indicus) bulls of ten each, superior and inferior quality semen producing bulls, which were classified based on their seminal quality parameters. For TSPY gene, the inferior quality semen donor group has significantly lower copy number than superior quality semen donor group (p < 0.05). No significant difference was found in DDX3Y and USP9Y gene copy numbers between two groups (p > 0.05). In conclusion, this study demonstrates that the copy number of TSPY, a Y chromosomal spermatogenesis related gene, may be an important determinant to predict the quality of bull semen, facilitating better selection of bulls in a herd for semen collection program.

Tolerance of spermatozoa to hypotonic stress: role of membrane fluidity and correlation with cryosurvival

The aim of this study was to evaluate inter-individual variability in osmotic properties of stallion spermatozoa and its correlation with cryosurvival. In addition, temperature dependency of hypo-osmotic tolerance and membrane fluidity were studied. Stallion sperm membranes exhibited good resistance towards hypotonic stress in the 15–30°C temperature range, whereas membrane stability was found to be decreased at 4 and 37°C. Bull spermatozoa showed greater hypo-osmotic tolerance compared with stallion spermatozoa, especially at temperatures above 30°C, which coincided with decreased membrane fluidity of bovine spermatozoa in this temperature range. The critical osmolality at 22°C, at which half of the sperm population survived exposure to hypotonic saline solution, was found to vary between 55 and 170 mOsm kg–1 among different stallions. Clear correlations were found for pre- versus post-freeze sperm motility and membrane integrity. Pre-freeze percentages of membrane-intact spermatozoa after exposure to hypotonic stress showed a weak correlation with sperm motility after cryopreservation. This correlation, however, was not found when data were corrected for initial numbers of membrane-intact spermatozoa in the sample. We thus conclude that studies on pre-freeze tolerance towards hypotonic stress cannot be used to predict sperm cryosurvival rates for individual stallions.

Review on the screening of semen by hypo-osmotic swelling test

The hypo-osmotic swelling test (HOST) is widely used as a valuable test for determining sperm quality by evaluating the membrane integrity of spermatozoa of various domestic animals including cattle, horses and swine. The HOST has also been used as an indicator of the fertilising capacity of spermatozoa. This test is based on the swelling ability when functional spermatozoa submitted to hypo-osmotic solutions. This test is commonly used as an important parameter for the evaluation of semen due to its strong correlation with semen evaluation parameters. The objective of this review was to analyse its significance in semen evaluation, swelling of spermatozoa under various osmolarities and variations in swelling percentage under different seasons.

Comparação entre duas concentrações de glicerol para a criopreservação de sêmen de suçuarana (Puma concolor)

O desenvolvimento de biotécnicas de reprodução é uma importante ferramenta para a conservação de animais silvestres ameaçados de extinção. Procedimentos de reprodução assistida em suçuarana, no entanto, são escassos na literatura, em especial aqueles relacionados à criopreservação de sêmen. Neste sentido, o presente trabalho objetivou avaliar a congelabilidade do sêmen de suçuaranas adultas mantidas em cativeiro, por meio da comparação entre duas concentrações de glicerol no meio de congelamento. Foram usados cinco machos adultos de suçuarana, mantidos no Centro de Reabilitação de Animais Silvestres do Mato Grosso do Sul (CRAS/MS). As amostras foram coletadas por eletroejaculação e avaliadas quanto ao seu aspecto físico, volume, vigor, motilidade, concentração e índice espermático. De cada ejaculado duas alíquotas foram diluídas em meio Tris-citrato-gema de ovo, em concentrações finais de 5 e 7,5% de glicerol, resfriadas a uma taxa de -0,55ºC/min e congeladas a uma taxa de -5,8ºC/min. Depois de descongeladas, as amostras foram reavaliadas e submetidas aos testes de termorresistência e hiposmótico. O protocolo de criopreservação e descongelamento de sêmen proposto se mostrou eficiente em ambas as concentrações de glicerol testadas, não havendo diferença (p>0,05) entre estas.

Retrospective analysis of canine semen evaluations with special emphasis on the use of the hypoosmotic swelling (HOS) test and acrosomal evaluation using Spermac(®)

Routine semen evaluation includes volume, motility, vital staining for live-dead ratio and pathomorphology including Spermac(®) staining for evaluation of the acrosome. In recent years, depending on the species, also the hypoosmotic swelling (HOS) test has been applied routinely for evaluation of semen quality. In this respect, a significant correlation between the ability of spermatozoa to swell in HOS test and the fertilizing ability has been reported. Also for evaluation of dog semen, reference has been made to the HOS test; however, its correlation to conventional semen parameters so far is discussed controversially. In the present study, the results of 400 semen examinations from stud dogs presented at our clinic were evaluated for their correlations between conventional semen parameters (motility, live/dead ratio, pathomorphology), conventional semen parameters and age, Spermac(®) staining and HOS test, respectively. We found a significant correlation of age and sperm concentration (p < 0.01), total sperm count (p < 0.0001), percentage of progressively motile sperm (p < 0.01) and live spermatozoa (p = 0.012). Furthermore, several correlations between conventional semen parameters were identified. Percentage of sperm with normal acrosome identified by Spermac (®) staining correlated significantly with live spermatozoa (p < 0.0001) and percentage of progressively motile sperm (p < 0.01). A significant correlation was proven between curled tails in HOS test and age (p < 0.001), motility (p < 0.0001), live sperm (p < 0.0001), acrosomal status (p < 0.05), pathomorphology (p < 0.0001) and sperm concentration (p = 0.011). These results indicate that Spermac(®) staining and the HOS test are useful in improving canine semen analysis.

Seminal parameters and field fertility of cryopreserved donkey jack semen after insemination of horse mares

REASONS FOR PERFORMING STUDY

As mule production is often concentrated in remote areas of the world, a simplified semen cryopreservation protocol is required.

AIM

To compare the seminal parameters of cryopreserved donkey semen in lactose-EDTA and lactose-yolk extenders and the fertility rates on horse mares.

METHODS

TRIAL 1: Sperm total and progressive motility, vigour (scale 0-5), morphology (major and minor defects) and plasma membrane integrity (HOST) were evaluated in 25 ejaculates from 5 donkey jacks immediately after collection (raw), after chilling to 5°C (chilled) and after freezing/thawing. The semen was mixed with skimmed-milk extender, centrifuged, and then re-suspended in lactose-EDTA or lactose-yolk extender. Semen was loaded into 0.5 ml straws and chilled to 5°C for 1 h, after which samples were either evaluated (chilled semen) or placed above liquid nitrogen for 20 min prior to immersion. Seminal parameters were evaluated by ANOVA and Tukey's test. TRIAL 2: Cryopreserved semen from 3 males was used to inseminate 53 mares at 60 oestrous cycles randomly assigned to lactose-yolk (n = 30 cycles) or lactose-EDTA (n = 30 cycles) extenders. Pregnancy diagnosis was performed 15 and 25 days post ovulation. The pregnancy rates were compared using Chi-squared tests.

RESULTS

TRIAL 1: No significant differences were evident in any seminal parameters between extenders after either chilling or cryopreservation. Total and progressive motility were significantly (P<0.05) lower in cryopreserved semen than raw and chilled semen for both extenders. TRIAL 2: Pregnancy rates did not significantly differ between extenders (lactose-EDTA extender 53.33 and 43.33%; lactose-yolk 50.0 and 46.66% for Days 15 and 25 post ovulation, respectively).

CONCLUSIONS

Cryopreservation of donkey semen using the simplified lactose-yolk extender resulted in similar seminal parameters and fertility rates when compared to lactose-EDTA extender.

POTENTIAL RELEVANCE

Lactose-yolk extender may be advocated as a simple, easy to prepare extender, for use in geographically isolated enterprises producing mules throughout the world.

Improved cryopreservability of stallion sperm using a sorbitol-based freezing extender

Cryopreservation of stallion semen is often associated with poor post-thaw sperm quality. Sugars are among the important components of a freezing extender and act as non-permeating cryoprotectants. This study aimed to compare the quality of stallion sperm frozen with glucose, fructose or sorbitol-containing freezing extenders. Semen was collected from six stallions of proven fertility and cryopreserved using a freezing extender containing different types of monosaccharide sugars (glucose, fructose or sorbitol). After thawing, the semen was examined for sperm motility, viability, acrosome integrity, plasma membrane functionality and sperm longevity. The fertility of semen frozen in the presence of sorbitol was also tested by artificial insemination. Sperm quality was significantly decreased following freezing and thawing (P < 0.05). Fructose was inferior for protecting sperm during cryopreservation when compared to sorbitol and glucose (P < 0.05). Although the viability, motility and acrosome integrity of sperm cryopreserved with a glucose-containing extender did not significantly differ from sperm frozen in the sorbitol-based extender when examined at 2 and 4 h post-thaw, all of these parameters plus plasma membrane functionality were improved for sperm frozen in the sorbitol extender than in the glucose extender when examined 10 min post-thaw. Two of four mares (50%) inseminated with semen frozen with a sorbitol-containing freezing extender became pregnant. It is concluded that different sugars have different abilities to protect against cryoinjury during freezing and thawing of stallion sperm. This study demonstrated that an extender containing sorbitol as primary sugar can be used to successfully cryopreserve equine sperm; moreover, the quality of frozen-thawed sperm appeared to be better than when glucose or fructose was the principle sugar in the freezing extender.

Freezability of equine semen after glass beads column separation

REASONS FOR PERFORMING STUDY

The success rate of artificial insemination following the freezing of stallion semen is limited; therefore, improving the stallion semen quality after the freezing and thawing process is a necessary objective.

OBJECTIVES

To investigate the influence of glass bead column separation on the freezability of stallion semen.

HYPOTHESIS

Glass beads in a column separator remove damaged and dead spermatozoa in the ejaculate during centrifugation.

METHODS

In total, 50 ejaculates from 6 Lipizzaner stallions were studied. Each ejaculate was divided into 2 parts, one half processed following standard procedure and the second half used for the column separation procedure. After freezing, semen quality was evaluated using standard tests for motility, morphology and viability of semen.

RESULTS

Motility and progressive motility of the column-separated (CS) semen were significantly higher (P < 0.001) before freezing and immediately, 24 and 48 h after thawing. A significant increase (P < 0.001) in the percentage of hypoosmotic positive spermatozoa was observed in CS samples. The percentage of total morphological changes in the separated samples before and after freezing was significantly lower (P < 0.001) compared with samples prepared using the standard procedure. A substantial decrease (P < 0.001) was found in the percentage of spermatozoa with damaged acrosomes. However, the percentage of spermatozoa with coiled tails was increased in the separated samples (P < 0.001).

CONCLUSIONS

Column separation before freezing has a positive effect on the quality of thawed equine semen.

POTENTIAL RELEVANCE

The quality of CS frozen/thawed samples indicates their potential use for increasing insemination success in mares.

Morphology and head morphometric characters of sperm in Thai native crossbred stallions

BACKGROUND

One of the semen quality parameters use to determine fertility is the percentage of sperm that express normal morphology. Sperm head morphometry is also correlated with fertility. The objectives of this study were 1) to investigate the sperm morphology and normal sperm head morphometry of Thai native crossbred stallions, and 2) to compare our results with the characteristics of proven fertile sperm from purebred stallions.

METHODS

Semen samples were collected monthly from nine stallions, of which five were Thai native crossbred (T) and four were purebred of proven fertility (F: F1 was a Standard-bred; F2 was a Warm-blood; F3 and F4 were Thoroughbreds). All the animals were aged between 5 and 12 years. Sperm morphological examination was performed using formaldehyde-fixed samples under phase-contrast microscopy (1000x). Normal sperm head morphometry characteristics were measured by Computer-Assisted Semen Analysis (Hamilton Thorne, USA.) after applying the Harris' haematoxylin staining technique.

RESULTS

The percentages of morphologically normal and abnormal sperm varied among individual stallions in both the T and F groups. The mean percentage of morphologically normal sperm was not significantly different (P > 0.05) between T and F stallions (mean +/- SE, 49.7 +/- 1.3 and 48.1 +/- 2.8, respectively). A comparison between the T and F sperm heads revealed that all the dimensional parameters were significantly different (P < 0.05). The coefficients of within-animal variation (CVs) ranged from 2.6 (shape factor 1) to 7.5 (elongation) and 2.9 (shape factor 1) to 8.1 (elongation) in T and F, respectively. In the case of the T group, those sperm head parameters that featured a low within-animal CV and a high between-animal CV were perimeter (2.9, 19.1), shape factor 1 (2.6, 25.8) and shape factor 3 (3.8, 32.0). In the case of the F group, only shape factor 1 (2.9, 26.1) featured such characteristics.

CONCLUSION

We found variability in the percentage of morphologically normal and abnormal sperm, as well as in sperm head dimensions among Thai native crossbred stallions, and these results were similar to those of purebred stallions. Our findings demonstrate that the heads of the T sperm specimens were larger and rounder than that of the F sperm. Perimeter, shape factor 1 and shape factor 3 could be used as parameters for the identification of individual T stallions based on a sperm sample.

Validation of the sperm mobility assay in boars and stallions

The sperm mobility assay used in the present study measures the rate of sperm penetration in a biologically inert cell-separation solution (Accudenz). When a sample of sperm is overlaid in a cuvette containing Accudenz, sperm penetrate the solution and absorbance of the sample can be measured with a spectrophotometer. This assay has been successfully used to select chicken and turkey semen donors. We validated this assay for semen from boars and stallions. Absorbance was measured after overlaying fresh semen from each species in prefilled cuvettes for 1, 5, 10, 15, 20, and 40 min. There were no significant differences when sperm were incubated in prewarmed cuvettes at 37, 39, or 41 degrees C. However, a minimum concentration of 5x10(7) viable sperm/mL was needed to evaluate the rate of sperm penetration in boars. Absorbance was half-maximal at 5.4 and 14.1 min for boar and stallion sperm, respectively. Frequency analysis suggested a normal distribution of mobility values for boar sperm. There were positive correlations between mobility values and several computer-aided sperm analysis (CASA) parameters. In addition, there was medium repeatability for multiple ejaculates from single males. We concluded that the mobility assay can be used for mammalian sperm and there seemed to be phenotypic variation among boars in mobility estimates.

Fertility of frozen-thawed stallion semen cannot be predicted by the currently used laboratory methods

The aim of the project was to use current simple and practical laboratory tests and compare results with the foaling rates of mares inseminated with commercially produced frozen semen. In Exp. 1, semen was tested from 27 and in Exp. 2 from 23 stallions; 19 stallions participated in both experiments. The mean number of mares per stallion in both experiments was 37 (min. 7, max. 121). Sperm morphology was assessed and bacterial culture performed once per stallion. In Exp. 1, progressive motility after 0, 1, 2, 3, and 4 h of incubation using light microscopy, motility characteristics measured with an automatic sperm analyzer, plasma membrane integrity using carboxyfluorescein diacetate/propidium iodide (CFDA/PI) staining and light microscopy, plasma membrane integrity using PI staining and a fluorometer, plasma membrane integrity using a resazurin reduction test, and sperm concentration were evaluated. In Exp. 2, the same tests as in Exp. 1 and a hypo-osmotic swelling test (HOST) using both light microscopy and a fluorometer were performed immediately after thawing and after a 3-h incubation. Statistical analysis was done separately to all stallions and to those having ≥ 20 mares; in addition, stallions with foaling rates < 60 or ≥ 60% were compared. In Exp. 1, progressive motility for all stallions after a 2 – 4-h incubation correlated with the foaling rate (correlation coefficients 0.39 – 0.51), (p < 0.05). In stallions with > 20 mares, the artificial insemination dose showed a correlation coefficient of -0.58 (p < 0.05). In Exp. 2, the HOST immediately after thawing showed a negative correlation with foaling rate (p < 0.05). No single test was consistently reliable for predicting the fertilizing capacity of semen, since the 2 experiments yielded conflicting results, although the same stallions sometimes participated in both. This shows the difficulty of frozen semen quality control in commercially produced stallion semen, and on the other hand, the difficulty of conducting fertility trials in horses.

Detection of damage in mammalian sperm cells

Ejaculated semen is washed for in vitro fertilization or diluted and processed to allow optimal and long-term low temperature liquid- and cryo-preservation. However, sperm are vulnerable to the washing, dilution, temperature and osmotic changes involved in sperm storage. In this review, a number of techniques are considered for detecting damaged spermatozoa. Staining protocols have been developed to detect the membrane and organelle integrity of mammalian sperm cells. Plasma membrane integrity is usually assessed after staining cells with membrane-impermeable dyes or alternatively with acetylated membrane (AM) permeable probes that are selectively de-esterified and become membrane impermeable and thus entrapped into viable cells only (AM ester loading). Organelle-specific dyes are commonly used to detect functionality of mitochondria or the acrosome. A distortion in the lateral and bilayer organization of lipids as well as the peroxidation of fatty acid moieties can be quantified and localized in living sperm. The relation of a disordering in the sperm membrane's lipid architecture and sperm deterioration versus capacitation is discussed. Finally, the integrity of sperm DNA can be measured at three different levels by assessing the degree of DNA-protamine condensation, the incidence of breaks and nicks in the DNA and the frequency of fragmentation of the nuclei into sub-haploid apoptotic bodies. The relevance of detecting DNA aberrations and especially the putative link to the incidence of apoptosis is critically considered.

Fertility evaluation of frozen/thawed semen

In vitro semen analyses have been used for more than half a century to estimate the fertilizing potential of a semen sample. Unfortunately, none of the assays developed provide results that consistently correlate well with fertility. The reasons for this lack of consistency, due in part to the complexity of the spermatozoon itself, the collection of fertility data, and factors beyond control of the semen analyses themselves, are discussed. Different spermatozoal attributes that are necessary for a spermatozoon to fertilize an oocyte are presented and assays used to evaluate each attribute described. Although laboratory assay results do not correlate well with semen fertility, the importance of conducting laboratory assays on every semen sample used for artificial insemination or to attempt to determine causes for infertility, is discussed.

Seasonal changes in semen quality and freezability in the Warmblood stallion

The objective of this study was to investigate seasonal changes in stallion semen quality and to determine the best time for semen cryopreservation. Experiments were performed using 10 Warmblood stallions from the National Stud Farm in Avenches (Switzerland). Ejaculates were collected and frozen every other week during 1 year from January to December 1999. Volume, concentration, and motility, and the number of morphologically normal sperm and sperm with major defects (abnormal heads, acrosome defects, nuclear vacuoles, proximal droplets, abnormal midpieces) were evaluated. For all frozen-thawed semen samples motility as well as viability (SYBR-14/PI) was tested, and the hypoosmotic swelling test (HOS) was performed. To analyze seasonal differences 4 periods of 3 months each were defined: autumn (September, October, November), winter (December, January, February), spring (March, April, May) and summer (June, July, August). During the 1 year experiment all semen quality parameters showed a clear seasonal pattern. The volume, total sperm count and motility in fresh semen were significantly higher (P<0.05) in summer than in winter, while sperm concentration was significantly lower in summer compared to the other seasons. Regarding morphology, normal sperm was significantly lower (P<0.05) in summer than at any other time of the year and higher values (P<0.05) were found for major defects in summer than in spring and autumn. In frozen-thawed semen motility was significantly (P<0.05) improved in autumn when compared to spring and summer. Viability was lowest in summer and differed significantly (P<0.05) from other seasons. The HOS test revealed significantly more (P<0.05) membrane damaged spermatozoa in winter than in spring, summer and autumn. Our results demonstrate that in our climatic conditions clear seasonal differences occur in semen quality of fresh and frozen-thawed semen and that cryopreservation of stallion semen should preferably be performed in autumn.