ARTIFICIAL INSEMINATION IN FARM ANIMALS - Phenix-Vet

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200Artificial Insemination in Farm Animalsglycocalyx components, peripheral proteins known to confer stability to the spermatozoa intheir passage through the female system. This will influence peripheral protein attachment,causing them to aggregate in the areas of membrane still in the fluid state once gel formationhas begun (Andrabi, 2007; Housley and Stanley, 1982). Many of these changes to membraneconfiguration involving lipids are known to be irreversible and subsequent warming of thespermatozoa does not restore the original membrane configuration.Another sperm alteration linked to freezing is related to the transfer of proteins through thecell, which is modulated by the distribution of lipids along the membrane, altering theresponse to induction of capacitation and the acrosome reaction of frozen/thawedspermatozoa during fertilization (Guthrie and Welch, 2005). Dislocation of proteins in theplasma membrane, such as those belonging to the glucose transporter (GLUT) family havealso been reported as major problem related to cryopreservation. These GLUT proteins aremainly responsible for the transport of hexose across mammalian sperm membranes (Kokket al, 2005). GLUT proteins have been detected in the spermatozoa membrane of dog (Rigauet al, 2002), human (Kokk et al, 2005) and boar (Medrano et al., 2006), highlighting theirimportant role in the regulation of sperm glucose and fructose metabolism.Ultrastructural studies have shown the presence of detrimental effects of cryopreservationon various sperm organelles such as altered spermatozoal mitochondria (Nishizono et al,2004). Microscopic examination of stallion spermatozoa indicates that the function of themitochondrial cristae is also affected by cold shock. This damage to mitochondrial structureand hence its function within the spermatozoa is likely to account for the decrease inmotility observed after freezing (Ruiz-Pesini et al, 2001). Moreover, swelling of theacrosomal area was observed to be a consequence of cold shock, which indicates a loss ofintegrity as membranes are normally unable to stretch. Freezing is also known to changemotion characteristics of spermatozoa due to the irreversible changes to the mid-piece andcoiling of the tail (Watson, 1990). Particularly in donkeys, spermatozoa show an increasedincidence of backward motion because of an over-bending of the tail area (Ayalew E. andLemma A., 2010; Tsega A. and Lemma A., 2009; Unpublished observation).Cryopreservation has also been shown to induce the acrosome reaction in spermatozoa.DNA integrity of sperm is essential for accurate transmission of paternal geneticinformation. Normal condensation and stabilization of sperm chromatin in the nucleusfollowed by decondensation after sperm penetration and injection into the cytoplasm of theoocyte are pre-requisites for fertilization. However, sperm chromatin structure and DNA areknown to be altered or damaged during cryopreservation (Donnelly et al, 2001; Fraser andStrzezek 2004; Hammadeh et al, 2001; Peris et al, 2004). It is reported that thecryopreservation process of freezing and thawing can increase abnormal chromatincondensation in human (Donnelly et al, 2001; Hammadeh et al, 2001; Royere et al, 1991), boar(Fraser and Strzezek, 2004), and ram (Peris et al, 2004) sperm. Normal chromatin packagingis also known to significantly decrease after the freeze-thawing procedure in human sperm.The chromatin structure of a mature spermatozoon is normally highly condensed, makingabout 5-10% in volume of that of a somatic cell. This packing is a result of a markedalteration in the composition of nucleoproteins that occurs during epididymal transit. Thespermatid genome encodes for protamines, a unique type of spermatozoal protein, whichpredominate as nucleoproteins during spermatozoal maturation in the epididymis. Thecysteine residues of this protein establish intramolecular and intermolecular disulfidelinkages that result in compaction and stabilization of the associated DNA. This design isbelieved to provide protection to the chromosomes during their transport within the female
Effect of Cryopreservation on Sperm Quality and Fertility 201reproductive tract (Varner and Johnson, 2007). It has been postulated that a reduction ofsperm surface area due to alteration of sperm chromatin may ultimately be manifested inabnormal morphology of the sperm head. A decrease in the percentage of normal spermheads in the ejaculate has been correlated with lowered fertility in bulls and overcondensationof chromatin appears to be associated with reduced fertility in men (Royere etal, 1991). Moreover, cryopreservation appears to reduce the ability of sperm chromatin todecondense. The adverse effects of cryopreservation on sperm chromatin and headmorphology may be responsible for lowered fertility of spermatozoa observed aftercryopreservation.3.3 Cpacitaion-like effect of cryopreservationOnce spermatozoa reach the site of fertilization, there appear to be highly coordinatedcellular and molecular events that should happen before the actual fertilization. The spermcells first attach temporarily to oviductal epithelial cells, a process that requires specific cellto cell attachment, possibly mediated through spermatozoal surface carbohydrate-bindingproteins, termed lectins (Varner and Johnson, 2007). They then undergo capacitation andhyperactivation, bind to the oocyte zona pellucida, undergo the acrosome reaction,penetrate the zona, and finally fuse with and penetrate the oolemma. Intracellular calciumlevels increase in sperm during capacitation, hyperactivation and the zona pellucidainducedacrosome reaction. Increased concentrations of calcium ions are believed to triggeran intracellular signalling way associated with capacitation. Capacitaion andcryopreservation induce several similar changes to the sperm including calcium influx in tothe cells (Bailey et al, 2000). However, during cryopreservation sperm cells fail to properlymoderate normal internal calcium levels. Restructured membranes and distorted lipidproteinassociations are believed to favour further calcium ion influx duringcryopreservation. Disruption of the normal capacitation and/or the acrosome reaction dueto abnormal concentrations of calcium ion would severely compromise the fertilizingpotential of spermatozoa post-thaw. On the other hand, cryopreserved sperm cells exhibit acapacitaion-like behaviour and appear to be in a partially capacitated state due to thecryopreservation-induced membrane changes that makes the cells to be more active to theirenvironment after thawing. As demonstrated by different authors, capacitaion normallycreates a state of destabilization with which the sperm cell acquires the fertilizing capacitywhile remaining susceptible to membrane degeneration and spontaneous acrosomalreaction when fertilization fails (Bailey et al, 2000). Cryopreservation creates a subpopulationof killed and partially or fully capaciatated sperm thereby reducing the heterogeneity of thesperm population. This will produce a sperm subpopulation with a shortened lifespan invivo and whose fertilization potential has been severely compromised reducing the fertilityof the semen sample as a whole.Capacitaion like effect or ‘Cryo-capacitation’ is one of the major factors associated withreduced longevity and poor survivability of cryopreserved spermatozoa in femalereproductive tract (Bailey et al, 2000; Watson, 2000), resulting in reduced fertility of frozenthawedsemen. At present, it is generally accepted that poor survival of spermatozoa in thefemale reproductive tract is among the most important consequences of sperm cryoinjurycaused by cryopreservation. This concept of premature capacitation and reduced longevityof sperm cells in the female reproductive tract has led to the routine use of oviductalinsemination by laparscopy rather than vaginal or even transcervical insemination indifferent animals (Bailey et al, 2000). The capacitation-like changes have been demonstrated
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VIContentsChapter 9Evaluation of a
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ARTIFICIAL INSEMINATION IN FARM ANIMALS - Phenix-Vet

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