Flow Cytometry for the Evaluation of Semen

blend Cytometry for the Evaluation of cumState of the Art in Sperm Assessment Using melt Cytometry short-changeFlow cytometry is emerging as a substantial tool in the do of import of modern andrology for the routine abstract of spermatozoanatozoon cellatozoon cellatozoa. Recent application of return cytometry in the artificial insemination industry oddly for horseshit is a new approach. Until genuinely recent, depth psychology of seed tastes was routinely performed by microscopicalal paygrade and manual techniques by research laboratory operators outline is inclined refer equal to(p)(p) to comprehensive variability among observers, influencing its clinical validity. During last decade, to measure farm animal seed, variety of new settle cytometric techniques receive been intercalated which made possible a wide-cut spread evaluation of several sperm working(a)ity and characteristics. Here in this paper, an initiative has been taken to explore numerous certain hunt cytometry developments pressing for andrological essays.After the foundation of period of age cytometry, sperm evaluation by traditional (microscopic) means became questi mavind and avoided delinquent to the deep advantages of run cytometry over the microscopic orders. By the recent development of various fluroscence probes, flow cytometry became cap satis doery of analyzing cast of sperm characteristics like viability, capacitation, acrosomal integrity, tissue layer permeability, tissue layer integrity, mitochondrial status, DNA integrity, decondensation of DNA and differences in the midst of gametes base of operations on sex. The application of flow cytometry to their perception allows in grooved rime of spermatozoa to be assessed over a short time-period, provides the opportunity of working with small sample sizes, increases the repeatability of selective information obtained, removes the subjectivity of evaluation and allows simultaneous discernment of multiple fluorochromes. Thus, flow cytometry is a technique capable of generating signifi shagtly novel selective information and allows the design and execution of experiments that argon not yet possible with some(prenominal) other(a) technique. Nowa mean solar days, come evaluation employ laboratory analyses is very meaningful to the artificial insemination industry to provide the to the highest degree desired timbre product to customers. prox development of flow cytometric techniques leave al unmatched permit further advances both in our k nowledge and in the improvement of aided reproduction techniques. In this paper, the main seminal fluid dimensions that finish be analyzed with fluorochromes and adapted for social occasion with a flow cytometer impart be reviewed and the relationship of these tests to fullness will be discussed.IntroductionUp to now, germ evaluation is considered as the most important laboratory test that has enabled us to rank and predic t clean cases of profusion (Jarow et al., 2002), in rankness or level off of potential sub- magnificence (Rodrguez- grocery storenez, 2007). Determination of the potential fertility of semen sample and, in the long run, of the male from which it has been collected is the last goal of semen evaluations in clinically healthy sires. Now a days, many a(prenominal) orders for the estimate the possible fertilizing capacity of a semen sample and, or in the word, of the male (reviewed by Dziuk 1996 Rodrguez-Martnez et al. 1997a Rodrguez-Martnez and Larsson 1998 Saacke et al. 1998 Larsson and Rodrguez-Martnez 2000 Rodrguez- Martnez 2000, 2003 Popwell and Flowers 2004 Graham and Moc 2005 Gillan et al. 2005) atomic numerate 18 existing. The methods routinely accustomed for evaluation of the quality of a semen sample involved an evaluation of general appearance, volume, pH, sperm soaking up, viability, syllable structure and motility. closely of these evaluations ar based on microsc opic analyses that and bankers bill relatively a few numbers of spermatozoa in spite of appearance a world. In most of the cases, these argon time-consuming replys obtained are controversial and are not translatable. It should likewise be noted that such formal techniques are apt to extreme inter-ejaculate variation, regular(a) when the laboratory methodology has been standardized. In the wake of this information, new opportunities lease arisen for the development of methods for the diagnosis of male infertility, many of which have been shown to viewing a prognostic honour that eludes conventional semen profiling. Moreover, ejaculated spermatozoa are nowadays handled for routine in assisted reproductive technologies, such as the artificial insemination of chilled, frozen-thawed or sexed semen, and IVF. During this long processes, number of stairs like semen extension, fluorophore loading, invisible and laser illumination, high- move sorting, cooling and cryopreserv ation are followed, which create a scope to oblige contrasting degrees of change in sperm mathematical functionality followed by suffer of damage to sperm membranes, organelles or the DNA content. Therefore, although several assays have been genuine to monitor these sperm parameters, recently it is being claimed by many groups that buck of those so-called procedures are incomplete, time consuming and laborious.Flow cytometry in diverse technical applications proposes many advantages for the depth psychology of sperm quality. Flow cytometry is a method where multiple fluorescences and light scattering cornerstone be induced allowing star cell or particles illumination in suspension while they flow very rapidly through a sensing area. The increasing use over the past decade of flow cytometry in the leading laboratories in human and vet andrology has dramatically increased our knowledge of sperm function at a lower place physiological and biotechnological conditions. Flow cyto meters is capable to acquire data from several sub universe of discourses within a sample in a few minutes, making it perfect for assessing heterogenous populations in a semen sample. Flow cytometry was ab initio developed in the 1960s, after that flow cytometry is performing automated separation of cells based on the unique recognition of cellular patterns in a population feasible (Hulett et al., 1969). Likewise, cellular patterns can be recognized by utilizing such a separation approach, in all(prenominal) cells within a population (Baumgarth and Roederer, 2000 Herzenberg et al., 2006).The firstborn notion of flow cytometry development was for medical exam and clinical applications such as haematology and oncology. Although still often research is going on these medical areas and taradiddle for the vast majority of publications on this robust technique, but during the past few years it is being employ in a diverse areas, such as bioprocess monitoring, pharmacology, toxicolo gy, environmental sciences, bacteriology and virology. Together with elevated use in many areas, recent advancement of flow cytometry increased its application in the reproductive biology curiously for andrology. Although flow cytometry may overestimate the population of unlabelled cells (Petrunkina and Harrison, 2009), plethora of research from our group in pig (Pena et al., 2003, 2004, 2005 Spjuth et al., 2007 Fernando et al., 2003 Saravia et al.,2005, 2007,2009 De Ambrogi et al., 2006 ) bull (Bergquist et al., 2007 Nagy et al., 2004 Januskauskas et al., 2003 Bergqvist et al., 2007 Hallap et al., 2005, 2006) stallion ( Kavak et al., 2003 Morrell et al., 2008) target that newly developed fluorescent fixture fixture stains and techniques of flow cytometry has made possible a more widespread analysis of semen quality at a biochemical, ultrastructural and functional level. Therefore, flow cytometry is the received technical solution for rapid, punctiliously uniform assessment of s perm suspensions.In this review we have described potentiality and scope of flow cytometry for the evaluation of semen, and the guidance in which this technique can be use in clinical applications for andrology based on both(prenominal) of our previous experiences.Definition of flow cytometryThe definition of a flow cytometer is an instrument which measures the properties of cells in a flowing stream or an instrument that can measure physical, as well as multi-colour fluorescence properties of cells flowing in a stream.In other word, cytometry is a method which measure physical and chemical attributes of cells or other particles. Such a measurement is made when cells or other particles pass in single file through some sort of measuring apparatus in a stream of fluid. The data obtained can be apply to understand and monitor biological processes and develop new methods and strategies for cell noticeion and quantification. Compared to other traditional analytical tools, where a sin gle valuate for severally attribute is obtained for the whole population, flow cytometry provides data for each and every particle detected. As cells differ in their metabolic or physiological states, flow cytometry allows us not only to detect a item cell type but also to find different subpopulations according to their structural or physiological parameters.Flow cytometry is a technique for measuring components (cells) and the properties of individual cells in liquid suspension. In essence, suspended cells are brought to a detector, one by one, by means of a flow channel. Fluidic devices under laminar flow define the trajectories and velocities that cells traverse across the detector, and fluorescence, absorbance, and light scattering are among the cell properties that can be detected. Flow sorting allows individual cells to be sorted on the basis of their measured properties, and one to three or more global properties of the cell can be measured. Flow cytometers and cell sorte rs fall in use of one or more excitation sources and one or two fluorescent dyes to measure and restrict several thousands of cells per second. Flow cytometry presents mark and microscopic expirys (Bunthof et al., 2001 Shleeva et al., 2002), which help to overcome the problems with the manual methods described above.Function and types of flow cytometryA flow cytometer is made of three main systems, fluidics, optics and electronics. ItI It can acquire data on all subpopulations within a sample, making it ideal for assessment of heterogenous population, such as spermatozoa. The adaptation of flow cytometry to sperm assessment came in to function when it was employ for measuring their DNA content (Evenson et al., 1980) and its application for analyzing semen has been increased rapidly in last decade. Flow cytometry is now applied for the evaluation semen such as sperm viability, acrosomal integrity, mitochondrial function, capacitation status, membrane fluidity, DNA status and so on. Continuous innovation of new fluorescent stains and techniques facilitated the flow cytometric evaluation of spermatozoa.Flow cytometry allows the musing of physical characteristics, such as cell size, shape and internal complexity, and any component or function of the spermatozoon that can be detected by a fluorochrome or fluorescently labeled compound. The analysis is objective, has a high level of experimental repeatability and has the advantage of being able to work with small sample sizes. Flow cytometry also has the capacity to detect labeling by multiple fluorochromes associated with individual spermatozoa, meaning that more than one sperm attribute can be assessed simultaneously. This feature has an added emolument for semen analysis, as few single sperm parameters show world-shattering correlation with fertility in vivo for semen within the acceptable range of atomic number 7 (Larsson and Rodriguez-Martinez, 2000) and it is the general statistics that the more sper m parameters can be tested, the more accurate the fertility prediction releases (Amman and Hammerstedt, 1993).There are two main types of flow cytometers-analysers and sorters are in use. Together with data collection on cells, sorters have the potentiality to sort cells with particular properties (defined by the flow cytometer operator) to extremely high purities. There are also a number of commercial flow cytometers that have been developed for particular analytical requirements. Partec manufacture a Ploidy Analyser and also a jail cell Counter Analyser. Optoflow has developed a flow cytometer for the rapid detection, characterization and enumeration of microorganisms. Luminex is developing engineering science for multiplexed analyte quantitation using a combination of microspheres, flow cytometry and high make haste digital processing.Advantages of FC compared to other conventional techniques to explore sperm structure and functionUse of authentic assays in the fertility clin ic and artificial insemination industries increasing day by day. In this respect, use of flow cytometry strength be an important attempt to resolve su stain problem with so called normally used manual method for the semen analysis. An additional source of laboratory variation is the low number of sperms analyzed with such techniques. It is worth mentinign here that so called method deal only with few hundred sperm. When we deal with such a few sperm population, there is a possibility that obtained result might not be statistically significant (Russel and Curtis, 1993). The methods which are frequently used are enable to determine sperm dousing (Jorgensen et al., 1997), motility or morphology only ( skunk et al., 2002). Objectivity, cell number measured, speed of view and precision are the advantages of flow cytometry to conventional light microscopy techniques (Spano and Evenson, 1993). The technique now a days has been used to determine a number of factors including those of acr osome status, membrane integrity, mitochondrial function as well as multiparameter measurement in human (Garrido et al., 2002). Flow cytometry has the ability to analyze thousands of cells in few minutes. In our series of studies, we demo the feasibleness and reproducibility of an automated method to evaluate sperm cell type, itemise, and viability in human hog samples. In our hand, the precision of the flow cytometric analysis is fitting in a diverse species (boar, bull, stallion etc), and the observed errors were significantly better than those obtained from the so-called manual methods.Although there are diverse benefits of flow cytometer for the analysis of semen, feasibility of applying flow cytometry sometimes restricted to researcher due to the high outlay and difficulties of operation associated with the requirement of a apt operator. farther, a flow cytometer is very too large and cannot resist shocks associated with sweat, and it also requires much space in the lab oratory. Whatever may be the limitation, the development of more cheap bench-top flow cytometers in recent time raised the potential essentialities to semen analysis.If the further application of flow cytometric analysis is considered further, it might be seen that it is growing popularities as a technique for assessing more than one sperm attribute, simultaneously. Compared to traditional microscopic techniques, flow cytometry analysis is allowing to found a far more simplified and objective method of semen analysis, especially in relation to fertilization with acrosome reactivity potential of spermatozoa (Uhler et al., 1993 Purvis et al., 1990 Carver-Ward et al., 1996).A large number of different techniques to estimate sperm concentration have been reported. In the mid-1990s a series of fixed-depth usable slides were evaluated as rapid and effective pieces of equipment for the estimate of sperm concentration. Data from a number of preliminary studies proposed that, at least in the 20-mm-depth format, such house resulted in a noticeable underestimate of sperm concentration compared to the gold standard (improved Neubauer hemocytometer). According to the World health Organization that such chambers, whilst convenient in that they can be used without dilution of the specimen, might lead to inaccuracy (World Health Organization, 1999). Data from Tomlinson and colleagues indicate that two proprietary disposable slides (Microcell, Conception Technologies, San Diego, Calif Leja, Leja Products, BV Nieuw- Vennep, The Netherlands) can result in a lower concentrations of sperm compared to the hemocytometer method (Tomlinson et al., 2001). In contrast, plenty of reports document unacceptable differences between different laboratories and even between different individuals, although fewer studies attempt to address these issues. So, what is wrong?Improvement of semen quality testing has been emphasizing in some reports (Jorgensen et al., 1997 Keel et al., 2000). But due to low number of sperm evaluation by the conventional method results in poor reproducibility. These problems might be overcome when using flow cytometry. The validation of method is a challenge due to its essentiality of having specific, precise, objective, and accurate evaluation to establish a correlation of fertility data or to predict potential of a semen sample accurately (Amann, 1989). In a fertility clinic, precision of data in important as the result of semen analysis is frequently used to manage fertility of a patient and treatment of the unfertile couples. Thus, it is important to take into consideration within and between laboratory variations for successful infertility treatments.sometimes its a matter of argument that compared to flow cytometry, fluorescent microscopy evaluate patterns of fluorescence rather than the fluorescence intensity. Flow cytometer has the lack of ability to discriminate sperm containing a fluorescent crisscross bound to the equatorial segm ent or over one of the acrosomal membranes (Parinaud et al., 1993 Mortimer and Camenzind, 1989 Mortimer et al., 1987). Tao et al. (1993) compared flow cytometry and epifluorescent microscopy with various lectins and indicated that there is almost no difference between methodologies for detection of the acrosome reaction. However, it has been argued that lectins do not bind specifically to the acrosomal region of the sperm (Purvis et al., 1990 Holden and Trounson, 1991) and that other binding sites can be easily high-and-mighty by epifluorescence microscopy, whereas flow cytometry identifies the signal from the sinless sperm.excessly, conventional light microscopic semen assessment is increasingly being replaced by fluorescent staining techniques, computer-assisted sperm analysis (CASA) systems, and flow cytometry (Pena et al., 2001 Verstegen et al., 2002). Additional advantages over existing techniques are that this approach is faster than the hemacytometer and that cellular detri tus, fat droplets, and other particulate material in extended semen are not erroneously counted as sperm, as often occurs with electronic cell counters. This method can also be used to determine the number of somatic cells in a semen sample.Application of flow cytometry for sperm countSperm count is an important predominant factor for the evaluation of sperm fertility potential. straight determination of sperm cell concentration is critical especially in AI industry because it provides assurance to customers that straws of extended semen contain the sperm numbers indicated which will help to decide appropriate doze especially for pig. Accuracy of sperm count is a parking area problem in the andrological laboratories and accurate measure of sperm concentration is particularly important for export in which verification of numbers may be required. identification number sperm counts can help to identify possible processing errors within a specific batch of semen or on a particular da y, should those errors occur. As sperm counting procedures become more refined, routine counting can be used to monitor subtle changes in daily semen processing that might affect the number of sperm packaged in a straw. Every time new and more accurate methods for the sperm count determinations are coming and being replaced by the older ones. Some laboratories are trying the Maklerm counting chamber (Seif- Medical, Haifa, Israel) and other improved hemacytometers, such as the MicroCellTM (Fertility Technologies, Inc., Natick, MA) however, these techniques will likely have standard lems alike(p) to those associated with the standard hemacytometers. Although hemacytometers are routinely used for sperm counts, due to the slow process and need for multiple measurements of each sample, the chance of error increase. Freund and Carol (ref) declared that a difference of 20% were not unusual between the determinations by the same technician. Electronic counters provide much more rapid count ing, are easier to use, and give more repeatable results among technicians. However, those instruments tend to include in the sperm count any somatic cells present, immature sperm forms, cytoplasmic droplets, debris, and bacteria, thereby inflating the concentration value (Ref). Spectrophotometer is recently being used in the AI industries to assess sperm concentration by determining turbidity of a semen sample using an instrument previously calibrated for sperm concentration with a hemacytometer or Coulter counter (Ref). The accuracy of this method depends on the methods used for spectrophotometer calibration. Although, sperm concentration can also be determined by spectrophotometrically, the debris present in the raw semen crease problem with misestimation. Sperm number in the frozen thawed semen is difficult to ascertain as most of the extender contain egg yolk particles, fats and other particles which affect measurement of sperm with electric automobile cell counter or spectro photometers (Evenson et al., 1993). On the other hand flow cytometry created possibilities of a rapid determination of sperm number in a precise form. It is the flow cytometry which can reduce intra-laboratory and inter-laboratory variation and conflict regarding sperm concentration assessment. Computer assisted semen analyzer is robust technique for analyzing sperm movement which can count sperm as well but such an analyzer most of the cases use some counting chamber or hemacytometer which itself can generate error. Although, hemacytometer was originally developed for blood cell counting, its use is now diverse including andrological laboratories for sperm counting.Around two-decade agone flow cytometry was suggested for sperm numbers in straws of cryopreserved bull semen. Christensen et al. (-) observed similar results for sperm count with flow cytometry and hemocytometer for a number of species. Now a day a simultaneous determination of sperm viability and sperm concentration is possible which can avoid the chance of occurring differences between ejaculates leading lack of coordination with line of merchandise fertility and laboratory analyses. Thus the present technology is more precise which can get rid of variation from handling the sperm sample and variation from pipetting and the analysis itself. Further, Prathalingam et al. (2006) conclude that there is similarities for sperm count result between flow cytometry and two newly approached method (image analysis and fluorescent plate reader) for sperm counting. Though, use of fluorescent plate was emphasized due to low cost and allowing large number of cells counting from a large number of ejaculates.Although flow cytometry has become a valuable instrument for andrological determinations, it is also doomed that sperm concentration by flow cytometry signify a higher value than the real one. The possibility arise might be due to that semen samples often contain some alien materials such as immature germ cells, epithelial cells, blood cells, cytoplasmic droplet, cellular debris etc. In the same way, frozen semen has higher chance to introduce such material as they contain diluents components especially egg yolk particles. These particles and cell debris might have frontal and side light scatter parameters those are similar to spermatozoa. Such sperm-count-overestimation problem arisen in our cases also, especially when we deal with frozen semen. Further it is also claimed that flow cytometry has a tendency to overestimate viable spermatozoa. We are also experienced with such dread which we guess might be due to that egg particles of extender are considered as viable cell as for its staining pattern. Our yet to publish data indicate that this problem can be copy by a centrifugation process and by using low concentration sample for evaluation with flow cytometry. actually recently Petrunkina and Harrison (2009) proposed a mathematical comparison for fixing this flow cytometric sp erm counting. Thus much research is going on and we hope such dissension will completely be obstinate near future to get advantage from this robust technology for sperm counting.Flow cytometry for detecting sperm intactness-Viability of spermatozoaThe viability of spermatozoa is a key determinant of sperm quality and prerequisite for successful fertilization. Viability of spermatozoa can be assessed by numerous methods, but many are slow and under the weather repeatable and subjectively assess only 100 to 200 spermatozoa per ejaculate. Merkies et al. (2000) compared different methods of viability evaluation. They concluded that Eosin-nigrosin overestimate viability while fluorescent microscope and flow cytometry estimate similar cut back of viability. Current flow cytometric procedures are able to simultaneously evaluate sperm cell viability together with some other attributes. This method has been successfully used for assessing spermatozoa viability in men ( collect and Johnso n, 1995), bulls (Garner et al., 1994 Thomas et al., 1998), boars (Rodrguez-Martnez, 2007 Garner and Johnson, 1995 Garner et al., 1996), rams (Garner and Johnson, 1995), rabbits (Garner and Johnson, 1995), mice (Garner and Johnson, 1995 Songsasen et al., 1997), poultry and wildfowl (Donoghue et al., 1995 Blanco et al., 2000) and honey bees (Collins and Donoghue, 1999 Collins, 2000) and in fish (Martin Flajshans et al., 2004).Considerable information has accumulated on the use of fluorescent staining protocols for assessing sperm viability (Evenson et al., 1982). The SYBR 14 staining of nucleic acids, especially in the sperm head, was very bright in living sperm. Good agreement was observed between the fluorescent staining method and the standard eosin-nigrosine viability test the flow cytometric method showed a precision level higher than that of the manual method.One of the first attempts to assess sperm viability utilized rhodamine 123 for determining potentiality of mitochondrial membrane while ethidium bromide for membrane integrity through flow cytometry (Garner et al., 1986). Other combinations that have been used to examine the functional capacity of sperm are carboxyfluorescein diacetate (CFDA) and propidium iodide (PI) (Garner et al., 1988 Watson et al., 1992) carboxydimethylfluorescein diacetate (CMFDA), R123, and PI (Ericsson et al., 1993 Thomas and Garner, 1994) and PI, pisum sativum agglutinin (PSA), and R123 (Graham et al., 1990).The most generally used sperm viability stain combinations is SYBR-14 and PI at present. This stains are now sold commercially as live/dead viability kit. When these two stains are combinely used, the nuclei of viable sperm take fluoresce putting green and membrane integrity confused cells take red stain. This staining technique has been used in a number of species, including the boar (Garner and Johnson, 1995 Saravia et al.,2005, 2007,2009). Although species differences do exist in the function of spermatozoa, the Live / perfectly stain may similarly have no adverse affect on fertilization in the equine, although it remains to be tested in this species. late a new instrument (Nucelocounter-SP100) has been introduced to evaluate sperm concentration 11 and viability. Due to the small size and low cost, this instrument has been attracted for field measurements of both concentration and viability. In our hand this instrument was also became utilitarian for the quick measurement of sperm concentration and viability in stallion (Morrell et al., 2010).Fluorescent probes such as H33258, requiring flow cytometric analysis with a laser that operates in the ultraviolet light range, are less commonly used as this is not a standard feature on the smaller analytical machines. However, one selection is to use a fluorometer. A fluorometer is a relatively low-cost piece of portable equipment that permits a rapid analysis to be carried out on a sample. Januskauskas et al. (2001) used H33258 to detect nonviable bu ll spermatozoa by fluorometry and obtained an inverse correlation between the change cells per cent and the field fertility. Another option is fluorescent attachments for computer-assisted semen analysis devices. For example, the IDENT fluorescence feature of the Hamilton-Thorne IVOS permits staining with H33258 allowing an assessment of sperm viability to be made along with motility.Fluorochromes used to assess sperm viability by both approach could be utilized in combination with each other. In that case, when CFDA is used combined with PI, three populations of cells as live, which are green dead, which are red and a troika population which is stained with both and represents dying spermatozoa can be identified. This combination was found useful by Almlid and Johnson (1988) for frozen-thawed boar spermatozoa for monitoring membrane damage at the time of evaluation of various freezing protocols. Further, Harrison and Vickers (1990) also noticed that this combination with a fluore scent microscope is effective indication of viability of fresh, incubated or cold-shocked spermatozoa in boar and ram. severalize to these, Garner et al. (1986) was failed to find a relationship between bull sperm viability and fertility when using combination of CFDA/PI .Flow cytometry for evaluating sperm viability appears to be a precious tool in the AI industry. When a high number of sperm is packed in each insemination dose, the effect of selecting the best ejaculates according to sperm viability has a relatively limited effect. However, sperm viability might be more important when combined with low-dose inseminations. The FACSCount AF flow cytometer also determines sperm concentration accurately and incisively during the same analysis (Christensen et al., 2004a). The combined assessment of sperm viability and concentration appears to be useful in the wake of astir(p) quality control at AI stations. Because of the results of this trial, this method has been implemented by D anish AI stations (Christensen et al., 2005). Relatively bright fluorescence was found also in the mitochondrial sheath of living sperm. But the utensil and mode of action by which SYBR-14 binds to the DNA of sperm is not known. It is know that PI stains nucleic acids by intercalating between the base pairs (Krishan, 1975). Viability stains can also be used in conjugation with fluorescently labeled plant lectins for simultaneous assessment of the plasma membrane integrity and the acrosome integrity (Nagy et al., 2003). It is imaginable that assessment of viability using SYBR-14 dye does not damage spermatozoa, since Garner et al. (5) found that insemination of boar sperm stained with SYBR-14 did not compromise fertilization or even the development of flushed porcine embryos in vitro.Non-viable sperms can be detected using the membrane-impermeable nucleic acid stains which positively identify dead spermatozoa by penetrating cells with damaged membranes. Plasma membrane which is int act will not permit these stains entering into the spermatozoa and staining the nucleus. Most frequently used stains include phenanthridines, for example propidium iodide (PI (Matyus, 1984) ethidium homodimer-1 (EthD-1 (Althouse et al., 1995), the cyanine Yo-Pro (Kavak, 2003) and the bizbenzimidazole Hoechst 33258 (Gundersen and Shapiro, 1984). After a series of comparison between fertility of cryopreserved stallion spermatozoa with a number of laboratory assessments of semen quality as assessed by flow cytometry using PI, Wilhelm et al. (1996) concluded that viability is the single laboratory assay that jibe with fertility.-Sperm plasma membrane integrityAlthough the sperm plasma membrane covers the entire cell, it consists of three distinct membrane compartments, one which covers the outer acrosomal membrane, one which covers the post acrosomal particle of the sperm head, and one which covers the middle and principal pieces. Sperm membrane is directly or indFlow Cytometry for th e Evaluation of SemenFlow Cytometry for the Evaluation of SemenState of the Art in Sperm Assessment Using Flow CytometryAbstractFlow cytometry is emerging as a substantial tool in the domain of modern andrology for the routine analysis of spermatozoa. Recent application of flow cytometry in the artificial insemination industry especially for pig is a new approach. Until very recent, analysis of semen samples was routinely performed by microscopical evaluation and manual techniques by laboratory operators analysis is inclined due to comprehensive variability among observers, influencing its clinical validity. During last decade, to evaluate farm animal semen, variety of new flow cytometric techniques have been intercalated which made possible a wide spread evaluation of several sperm functionality and characteristics. Here in this paper, an initiative has been taken to explore numerous current flow cytometry developments pressing for andrological tests.After the invention of flow cyt ometry, sperm evaluation by traditional (microscopic) means became questioned and avoided due to the robust advantages of flow cytometry over the microscopic methods. By the recent development of diverse fluroscence probes, flow cytometry became capable of analyzing number of sperm characteristics like viability, capacitation, acrosomal integrity, membrane permeability, membrane integrity, mitochondrial status, DNA integrity, decondensation of DNA and differences between gametes based on sex. The application of flow cytometry to their detection allows increased numbers of spermatozoa to be assessed over a short time-period, provides the opportunity of working with small sample sizes, increases the repeatability of data obtained, removes the subjectivity of evaluation and allows simultaneous assessment of multiple fluorochromes. Thus, flow cytometry is a technique capable of generating significantly novel data and allows the design and execution of experiments that are not yet possib le with any other technique. Nowadays, semen evaluation using laboratory analyses is very meaningful to the artificial insemination industry to provide the most desired quality product to customers.Future development of flow cytometric techniques will permit further advances both in our knowledge and in the improvement of assisted reproduction techniques. In this paper, the main semen attributes that can be analyzed with fluorochromes and adapted for use with a flow cytometer will be reviewed and the relationship of these tests to fertility will be discussed.IntroductionUp to now, semen evaluation is considered as the most important laboratory test that has enabled us to identify and predict clear-cut cases of fertility (Jarow et al., 2002), infertility or even of potential sub-fertility (Rodrguez-Martnez, 2007). Determination of the potential fertility of semen sample and, in the long run, of the male from which it has been collected is the ultimate goal of semen evaluations in cli nically healthy sires. Now a days, many methods for the estimate the possible fertilizing capacity of a semen sample and, or in the word, of the male (reviewed by Dziuk 1996 Rodrguez-Martnez et al. 1997a Rodrguez-Martnez and Larsson 1998 Saacke et al. 1998 Larsson and Rodrguez-Martnez 2000 Rodrguez- Martnez 2000, 2003 Popwell and Flowers 2004 Graham and Moc 2005 Gillan et al. 2005) are existing. The methods routinely accustomed for evaluation of the quality of a semen sample involved an evaluation of general appearance, volume, pH, sperm concentration, viability, morphology and motility. Most of these evaluations are based on microscopic analyses that only measure relatively a few numbers of spermatozoa within a population. In most of the cases, these are time-consuming results obtained are controversial and are not translatable. It should also be noted that such conventional techniques are apt to extreme inter-ejaculate variation, even when the laboratory methodology has been stand ardized. In the wake of this information, new opportunities have arisen for the development of methods for the diagnosis of male infertility, many of which have been shown to exhibit a prognostic value that eludes conventional semen profiling. Moreover, ejaculated spermatozoa are nowadays handled for use in assisted reproductive technologies, such as the artificial insemination of chilled, frozen-thawed or sexed semen, and IVF. During this long processes, number of steps like semen extension, fluorophore loading, ultraviolet and laser illumination, high-speed sorting, cooling and cryopreservation are followed, which create a scope to impose different degrees of change in sperm functionality followed by suffer of damage to sperm membranes, organelles or the DNA content. Therefore, although several assays have been developed to monitor these sperm parameters, recently it is being claimed by many groups that buck of those so-called procedures are incomplete, time consuming and laboriou s.Flow cytometry in diverse technical applications proposes many advantages for the analysis of sperm quality. Flow cytometry is a method where multiple fluorescences and light scattering can be induced allowing single cell or particles illumination in suspension while they flow very rapidly through a sensing area. The increasing use over the past decade of flow cytometry in the leading laboratories in human and veterinary andrology has dramatically increased our knowledge of sperm function under physiological and biotechnological conditions. Flow cytometers is capable to acquire data from several subpopulations within a sample in a few minutes, making it perfect for assessing heterogenous populations in a semen sample. Flow cytometry was initially developed in the 1960s, after that flow cytometry is performing automated separation of cells based on the unique recognition of cellular patterns in a population feasible (Hulett et al., 1969). Likewise, cellular patterns can be recogniz ed by utilizing such a separation approach, in each cells within a population (Baumgarth and Roederer, 2000 Herzenberg et al., 2006).The first notion of flow cytometry development was for medical and clinical applications such as haematology and oncology. Although still much research is going on these medical areas and account for the vast majority of publications on this robust technique, but during the past few years it is being used in a diverse areas, such as bioprocess monitoring, pharmacology, toxicology, environmental sciences, bacteriology and virology. Together with elevated use in many areas, recent advancement of flow cytometry increased its application in the reproductive biology especially for andrology. Although flow cytometry may overestimate the population of unlabelled cells (Petrunkina and Harrison, 2009), plethora of research from our group in pig (Pena et al., 2003, 2004, 2005 Spjuth et al., 2007 Fernando et al., 2003 Saravia et al.,2005, 2007,2009 De Ambrogi et al., 2006 ) bull (Bergquist et al., 2007 Nagy et al., 2004 Januskauskas et al., 2003 Bergqvist et al., 2007 Hallap et al., 2005, 2006) stallion ( Kavak et al., 2003 Morrell et al., 2008) indicate that newly developed fluorescent stains and techniques of flow cytometry has made possible a more widespread analysis of semen quality at a biochemical, ultrastructural and functional level. Therefore, flow cytometry is the current technical solution for rapid, precisely reproducible assessment of sperm suspensions.In this review we have described potentiality and scope of flow cytometry for the evaluation of semen, and the way in which this technique can be used in clinical applications for andrology based on some of our previous experiences.Definition of flow cytometryThe definition of a flow cytometer is an instrument which measures the properties of cells in a flowing stream or an instrument that can measure physical, as well as multi-colour fluorescence properties of cells flowing in a stream.In other word, cytometry is a method which measure physical and chemical attributes of cells or other particles. Such a measurement is made when cells or other particles pass in single file through some sort of measuring apparatus in a stream of fluid. The data obtained can be used to understand and monitor biological processes and develop new methods and strategies for cell detection and quantification. Compared to other traditional analytical tools, where a single value for each attribute is obtained for the whole population, flow cytometry provides data for each and every particle detected. As cells differ in their metabolic or physiological states, flow cytometry allows us not only to detect a particular cell type but also to find different subpopulations according to their structural or physiological parameters.Flow cytometry is a technique for measuring components (cells) and the properties of individual cells in liquid suspension. In essence, suspended cells are broug ht to a detector, one by one, by means of a flow channel. Fluidic devices under laminar flow define the trajectories and velocities that cells traverse across the detector, and fluorescence, absorbance, and light scattering are among the cell properties that can be detected. Flow sorting allows individual cells to be sorted on the basis of their measured properties, and one to three or more global properties of the cell can be measured. Flow cytometers and cell sorters make use of one or more excitation sources and one or two fluorescent dyes to measure and characterize several thousands of cells per second. Flow cytometry presents objective and precise results (Bunthof et al., 2001 Shleeva et al., 2002), which help to overcome the problems with the manual methods described above.Function and types of flow cytometryA flow cytometer is made of three main systems, fluidics, optics and electronics. ItI It can acquire data on all subpopulations within a sample, making it ideal for asses sment of heterogenous population, such as spermatozoa. The adaptation of flow cytometry to sperm assessment came in to function when it was used for measuring their DNA content (Evenson et al., 1980) and its application for analyzing semen has been increased rapidly in last decade. Flow cytometry is now applied for the evaluation semen such as sperm viability, acrosomal integrity, mitochondrial function, capacitation status, membrane fluidity, DNA status and so on. Continuous innovation of new fluorescent stains and techniques facilitated the flow cytometric evaluation of spermatozoa.Flow cytometry allows the observation of physical characteristics, such as cell size, shape and internal complexity, and any component or function of the spermatozoon that can be detected by a fluorochrome or fluorescently labeled compound. The analysis is objective, has a high level of experimental repeatability and has the advantage of being able to work with small sample sizes. Flow cytometry also ha s the capacity to detect labeling by multiple fluorochromes associated with individual spermatozoa, meaning that more than one sperm attribute can be assessed simultaneously. This feature has an added benefit for semen analysis, as few single sperm parameters show significant correlation with fertility in vivo for semen within the acceptable range of normality (Larsson and Rodriguez-Martinez, 2000) and it is the general statistics that the more sperm parameters can be tested, the more accurate the fertility prediction becomes (Amman and Hammerstedt, 1993).There are two main types of flow cytometers-analysers and sorters are in use. Together with data collection on cells, sorters have the potentiality to sort cells with particular properties (defined by the flow cytometer operator) to extremely high purities. There are also a number of commercial flow cytometers that have been developed for particular analytical requirements. Partec manufacture a Ploidy Analyser and also a Cell Count er Analyser. Optoflow has developed a flow cytometer for the rapid detection, characterization and enumeration of microorganisms. Luminex is developing technology for multiplexed analyte quantitation using a combination of microspheres, flow cytometry and high speed digital processing.Advantages of FC compared to other conventional techniques to explore sperm structure and functionUse of authentic assays in the fertility clinic and artificial insemination industries increasing day by day. In this respect, use of flow cytometry might be an important attempt to resolve sustaining problem with so called commonly used manual method for the semen analysis. An additional source of laboratory variation is the low number of sperms analyzed with such techniques. It is worth mentinign here that so called method deal only with few hundred sperm. When we deal with such a few sperm population, there is a possibility that obtained result might not be statistically significant (Russel and Curtis, 1993). The methods which are frequently used are enable to determine sperm concentration (Jorgensen et al., 1997), motility or morphology only (Keel et al., 2002). Objectivity, cell number measured, speed of count and precision are the advantages of flow cytometry to conventional light microscopy techniques (Spano and Evenson, 1993). The technique now a days has been used to determine a number of factors including those of acrosome status, membrane integrity, mitochondrial function as well as multiparameter measurement in human (Garrido et al., 2002). Flow cytometry has the ability to analyze thousands of cells in few minutes. In our series of studies, we demonstrated the feasibility and reproducibility of an automated method to evaluate sperm cell type, count, and viability in human boar samples. In our hand, the precision of the flow cytometric analysis is satisfactory in a diverse species (boar, bull, stallion etc), and the observed errors were significantly better than those obt ained from the so-called manual methods.Although there are diverse benefits of flow cytometer for the analysis of semen, feasibility of applying flow cytometry sometimes restricted to researcher due to the high outlay and difficulties of operation associated with the requirement of a skilled operator. Further, a flow cytometer is very large and cannot resist shocks associated with movement, and it also requires much space in the laboratory. Whatever may be the limitation, the development of more affordable bench-top flow cytometers in recent time raised the potential essentialities to semen analysis.If the further application of flow cytometric analysis is considered further, it might be seen that it is growing popularities as a technique for assessing more than one sperm attribute, simultaneously. Compared to traditional microscopic techniques, flow cytometry analysis is allowing to give a far more simplified and objective method of semen analysis, especially in relation to fertili zation with acrosome reactivity potential of spermatozoa (Uhler et al., 1993 Purvis et al., 1990 Carver-Ward et al., 1996).A large number of different techniques to estimate sperm concentration have been reported. In the mid-1990s a series of fixed-depth disposable slides were evaluated as rapid and effective pieces of equipment for the estimate of sperm concentration. Data from a number of preliminary studies proposed that, at least in the 20-mm-depth format, such chambers resulted in a noticeable underestimate of sperm concentration compared to the gold standard (improved Neubauer hemocytometer). According to the World Health Organization that such chambers, whilst convenient in that they can be used without dilution of the specimen, might lead to inaccuracy (World Health Organization, 1999). Data from Tomlinson and colleagues indicate that two proprietary disposable slides (Microcell, Conception Technologies, San Diego, Calif Leja, Leja Products, BV Nieuw- Vennep, The Netherlands ) can result in a lower concentrations of sperm compared to the hemocytometer method (Tomlinson et al., 2001). In contrast, plenty of reports document unacceptable differences between different laboratories and even between different individuals, although fewer studies attempt to address these issues. So, what is wrong?Improvement of semen quality testing has been emphasizing in some reports (Jorgensen et al., 1997 Keel et al., 2000). But due to low number of sperm evaluation by the conventional method results in poor reproducibility. These problems might be overcome when using flow cytometry. The validation of method is a challenge due to its essentiality of having specific, precise, objective, and accurate evaluation to establish a correlation of fertility data or to predict potential of a semen sample accurately (Amann, 1989). In a fertility clinic, precision of data in important as the result of semen analysis is frequently used to manage fertility of a patient and treatment of the unfertile couples. Thus, it is important to take into consideration within and between laboratory variations for successful infertility treatments.Sometimes its a matter of argument that compared to flow cytometry, fluorescent microscopy evaluate patterns of fluorescence rather than the fluorescence intensity. Flow cytometer has the lack of ability to discriminate sperm containing a fluorescent marker bound to the equatorial segment or over one of the acrosomal membranes (Parinaud et al., 1993 Mortimer and Camenzind, 1989 Mortimer et al., 1987). Tao et al. (1993) compared flow cytometry and epifluorescent microscopy with various lectins and indicated that there is almost no difference between methodologies for detection of the acrosome reaction. However, it has been argued that lectins do not bind specifically to the acrosomal region of the sperm (Purvis et al., 1990 Holden and Trounson, 1991) and that other binding sites can be easily distinguished by epifluorescence microscopy , whereas flow cytometry identifies the signal from the entire sperm.Additionally, conventional light microscopic semen assessment is increasingly being replaced by fluorescent staining techniques, computer-assisted sperm analysis (CASA) systems, and flow cytometry (Pena et al., 2001 Verstegen et al., 2002). Additional advantages over existing techniques are that this approach is faster than the hemacytometer and that cellular debris, fat droplets, and other particulate material in extended semen are not erroneously counted as sperm, as often occurs with electronic cell counters. This method can also be used to determine the number of somatic cells in a semen sample.Application of flow cytometry for sperm countSperm count is an important predominant factor for the evaluation of sperm fertility potential.Accurate determination of sperm cell concentration is critical especially in AI industry because it provides assurance to customers that straws of extended semen contain the sperm nu mbers indicated which will help to decide appropriate doze especially for pig. Accuracy of sperm count is a common problem in the andrological laboratories and accurate measure of sperm concentration is particularly important for export in which verification of numbers may be required. Routine sperm counts can help to identify possible processing errors within a specific batch of semen or on a particular day, should those errors occur. As sperm counting procedures become more refined, routine counting can be used to monitor subtle changes in daily semen processing that might affect the number of sperm packaged in a straw. Every time new and more accurate methods for the sperm count determinations are coming and being replaced by the older ones. Some laboratories are trying the Maklerm counting chamber (Seif- Medical, Haifa, Israel) and other improved hemacytometers, such as the MicroCellTM (Fertility Technologies, Inc., Natick, MA) however, these techniques will likely have standard lems similar to those associated with the standard hemacytometers. Although hemacytometers are routinely used for sperm counts, due to the slow process and need for multiple measurements of each sample, the chance of error increase. Freund and Carol (ref) stated that a difference of 20% were not unusual between the determinations by the same technician. Electronic counters provide much more rapid counting, are easier to use, and give more repeatable results among technicians. However, those instruments tend to include in the sperm count any somatic cells present, immature sperm forms, cytoplasmic droplets, debris, and bacteria, thereby inflating the concentration value (Ref). Spectrophotometer is recently being used in the AI industries to assess sperm concentration by determining turbidity of a semen sample using an instrument previously calibrated for sperm concentration with a hemacytometer or Coulter counter (Ref). The accuracy of this method depends on the methods used for spe ctrophotometer calibration. Although, sperm concentration can also be determined by spectrophotometrically, the debris present in the raw semen crease problem with misestimation. Sperm number in the frozen thawed semen is difficult to ascertain as most of the extender contain egg yolk particles, fats and other particles which affect measurement of sperm with electric cell counter or spectrophotometers (Evenson et al., 1993). On the other hand flow cytometry created possibilities of a rapid determination of sperm number in a precise form. It is the flow cytometry which can reduce intra-laboratory and inter-laboratory variation and conflict regarding sperm concentration assessment. Computer assisted semen analyzer is robust technique for analyzing sperm movement which can count sperm as well but such an analyzer most of the cases use some counting chamber or hemacytometer which itself can generate error. Although, hemacytometer was originally developed for blood cell counting, its use is now diverse including andrological laboratories for sperm counting.Around two-decade ago flow cytometry was suggested for sperm numbers in straws of cryopreserved bull semen. Christensen et al. (-) observed similar results for sperm count with flow cytometry and hemocytometer for a number of species. Now a day a simultaneous determination of sperm viability and sperm concentration is possible which can avoid the chance of occurring differences between ejaculates leading lack of coordination with field fertility and laboratory analyses. Thus the present technology is more precise which can get rid of variation from handling the sperm sample and variation from pipetting and the analysis itself. Further, Prathalingam et al. (2006) concluded that there is similarities for sperm count result between flow cytometry and two newly approached method (image analysis and fluorescent plate reader) for sperm counting. Though, use of fluorescent plate was emphasized due to low cost and allowi ng large number of cells counting from a large number of ejaculates.Although flow cytometry has become a valuable instrument for andrological determinations, it is also blamed that sperm concentration by flow cytometry signify a higher value than the real one. The possibility arise might be due to that semen samples often contain some alien materials such as immature germ cells, epithelial cells, blood cells, cytoplasmic droplet, cellular debris etc. In the same way, frozen semen has higher chance to introduce such material as they contain diluents components especially egg yolk particles. These particles and cell debris might have frontal and side light scatter parameters those are similar to spermatozoa. Such sperm-count-overestimation problem arisen in our cases also, especially when we deal with frozen semen. Further it is also claimed that flow cytometry has a tendency to overestimate viable spermatozoa. We are also experienced with such trouble which we guess might be due to t hat egg particles of extender are considered as viable cell as for its staining pattern. Our yet to publish data indicate that this problem can be mimic by a centrifugation process and by using low concentration sample for evaluation with flow cytometry. Very recently Petrunkina and Harrison (2009) proposed a mathematical equation for fixing this flow cytometric sperm counting. Thus much research is going on and we hope such discrepancy will completely be resolved near future to get advantage from this robust technology for sperm counting.Flow cytometry for detecting sperm intactness-Viability of spermatozoaThe viability of spermatozoa is a key determinant of sperm quality and prerequisite for successful fertilization. Viability of spermatozoa can be assessed by numerous methods, but many are slow and poorly repeatable and subjectively assess only 100 to 200 spermatozoa per ejaculate. Merkies et al. (2000) compared different methods of viability evaluation. They concluded that Eosin -nigrosin overestimate viability while fluorescent microscope and flow cytometry estimate similar trend of viability. Current flow cytometric procedures are able to simultaneously evaluate sperm cell viability together with some other attributes. This method has been successfully used for assessing spermatozoa viability in men (Garner and Johnson, 1995), bulls (Garner et al., 1994 Thomas et al., 1998), boars (Rodrguez-Martnez, 2007 Garner and Johnson, 1995 Garner et al., 1996), rams (Garner and Johnson, 1995), rabbits (Garner and Johnson, 1995), mice (Garner and Johnson, 1995 Songsasen et al., 1997), poultry and wildfowl (Donoghue et al., 1995 Blanco et al., 2000) and honey bees (Collins and Donoghue, 1999 Collins, 2000) and in fish (Martin Flajshans et al., 2004).Considerable information has accumulated on the use of fluorescent staining protocols for assessing sperm viability (Evenson et al., 1982). The SYBR 14 staining of nucleic acids, especially in the sperm head, was very brig ht in living sperm. Good agreement was observed between the fluorescent staining method and the standard eosin-nigrosine viability test the flow cytometric method showed a precision level higher than that of the manual method.One of the first attempts to assess sperm viability utilized rhodamine 123 for determining potentiality of mitochondrial membrane while ethidium bromide for membrane integrity through flow cytometry (Garner et al., 1986). Other combinations that have been used to examine the functional capacity of sperm are carboxyfluorescein diacetate (CFDA) and propidium iodide (PI) (Garner et al., 1988 Watson et al., 1992) carboxydimethylfluorescein diacetate (CMFDA), R123, and PI (Ericsson et al., 1993 Thomas and Garner, 1994) and PI, pisum sativum agglutinin (PSA), and R123 (Graham et al., 1990).The most generally used sperm viability stain combinations is SYBR-14 and PI at present. This stains are now sold commercially as live/dead viability kit. When these two stains are combinely used, the nuclei of viable sperm take fluoresce green and membrane integrity lost cells take red stain. This staining technique has been used in a number of species, including the boar (Garner and Johnson, 1995 Saravia et al.,2005, 2007,2009). Although species differences do exist in the function of spermatozoa, the Live/Dead stain may similarly have no adverse affect on fertilization in the equine, although it remains to be tested in this species. Recently a new instrument (Nucelocounter-SP100) has been introduced to evaluate sperm concentration 11 and viability. Due to the small size and low cost, this instrument has been attracted for field measurements of both concentration and viability. In our hand this instrument was also became useful for the quick measurement of sperm concentration and viability in stallion (Morrell et al., 2010).Fluorescent probes such as H33258, requiring flow cytometric analysis with a laser that operates in the ultraviolet light range, are le ss commonly used as this is not a standard feature on the smaller analytical machines. However, one alternative is to use a fluorometer. A fluorometer is a relatively low-cost piece of portable equipment that permits a rapid analysis to be carried out on a sample. Januskauskas et al. (2001) used H33258 to detect nonviable bull spermatozoa by fluorometry and obtained an inverse correlation between the damaged cells per cent and the field fertility. Another option is fluorescent attachments for computer-assisted semen analysis devices. For example, the IDENT fluorescence feature of the Hamilton-Thorne IVOS permits staining with H33258 allowing an assessment of sperm viability to be made along with motility.Fluorochromes used to assess sperm viability by both approach could be utilized in combination with each other. In that case, when CFDA is used combined with PI, three populations of cells as live, which are green dead, which are red and a third population which is stained with both and represents dying spermatozoa can be identified. This combination was found useful by Almlid and Johnson (1988) for frozen-thawed boar spermatozoa for monitoring membrane damage at the time of evaluation of various freezing protocols. Further, Harrison and Vickers (1990) also noticed that this combination with a fluorescent microscope is effective indicator of viability of fresh, incubated or cold-shocked spermatozoa in boar and ram. Contrasting to these, Garner et al. (1986) was failed to find a relationship between bull sperm viability and fertility when using combination of CFDA/PI .Flow cytometry for evaluating sperm viability appears to be a precious tool in the AI industry. When a high number of sperm is packed in each insemination dose, the effect of selecting the best ejaculates according to sperm viability has a relatively limited effect. However, sperm viability might be more important when combined with low-dose inseminations. The FACSCount AF flow cytometer also dete rmines sperm concentration accurately and precisely during the same analysis (Christensen et al., 2004a). The combined assessment of sperm viability and concentration appears to be useful in the wake of improving quality control at AI stations. Because of the results of this trial, this method has been implemented by Danish AI stations (Christensen et al., 2005). Relatively bright fluorescence was found also in the mitochondrial sheath of living sperm. But the mechanism and mode of action by which SYBR-14 binds to the DNA of sperm is not known. It is know that PI stains nucleic acids by intercalating between the base pairs (Krishan, 1975). Viability stains can also be used in conjugation with fluorescently labeled plant lectins for simultaneous assessment of the plasma membrane integrity and the acrosome integrity (Nagy et al., 2003). It is conceivable that assessment of viability using SYBR-14 dye does not damage spermatozoa, since Garner et al. (5) found that insemination of boar sperm stained with SYBR-14 did not compromise fertilization or even the development of flushed porcine embryos in vitro.Non-viable sperms can be detected using the membrane-impermeable nucleic acid stains which positively identify dead spermatozoa by penetrating cells with damaged membranes. Plasma membrane which is intact will not permit these stains entering into the spermatozoa and staining the nucleus. Most frequently used stains include phenanthridines, for example propidium iodide (PI (Matyus, 1984) ethidium homodimer-1 (EthD-1 (Althouse et al., 1995), the cyanine Yo-Pro (Kavak, 2003) and the bizbenzimidazole Hoechst 33258 (Gundersen and Shapiro, 1984). After a series of comparison between fertility of cryopreserved stallion spermatozoa with a number of laboratory assessments of semen quality as assessed by flow cytometry using PI, Wilhelm et al. (1996) concluded that viability is the single laboratory assay that correlated with fertility.-Sperm plasma membrane integrityAlthou gh the sperm plasma membrane covers the entire cell, it consists of three distinct membrane compartments, one which covers the outer acrosomal membrane, one which covers the post acrosomal portion of the sperm head, and one which covers the middle and principal pieces. Sperm membrane is directly or ind