Reproduction in Domestic Animals

340 D Rath and LA JohnsonCommercial Application of Sex-SortedSpermatozoa in Livestock ProductionExcellent reviews on the commercialization, especially ofbovine sexed semen, have been published by Amann(1999), Seidel (2003a,b), Garner (2006) and Garner andSeidel (2008). Although their calculation models aremainly directed to the American farm situation, they arehelpful guidelines for other countries too. The situationin other species had been summarized by Maxwell et al.(2004) and for pigs by Johnson et al. (2005). Spermsorting based on the Beltsville Sperm Sexing Technologyhas reached a certain technical standard that makes itrobust enough for use under practical conditions, even ifit has clear limitations as described above. Its utilizationdiffers significantly among species mainly because of thebiological differences related to site of semen deposition,length of cycle, demand on sperm numbers, sortabilityand freezability of spermatozoa as well as commercialdemands and management conditions.The Commercial Use of Bovine Sex-SortedSemenStage of applicabilityDue to the high sorting index (131), an approximation ofthe ability to flow cytometrically sort sperm consisting ofthe head profile area (lm 2 ) · X-Y sperm DNA difference(%; Garner 2006), bovine spermatozoa are more suitablefor high-speed sorting than other species. The methodhas reached a standard that is likely to make it profitablein dairy herds soon. However, impairments to thefertilizing capacity of sorted bull sperm are obviousand impairment of fertilizing capacity because of theimpact of sorting and high dilution on capacitation andseminal plasma components continue to be limitations tobe dealt with. Further improvement of the pre- and postsorthandling of the semen is critical and requiresintensive research to minimize negative effects on thepost-thaw lifespan of sexed spermatozoa as the fertilephase has direct implications on AI regimens. In a recentstudy employing a modified sperm handling protocolduring sorting and freezing and in combination with anew extender for both sorting and freezing (Sexcess Ò ,Masterrind GmbH, Verden, Germany), we were able toextend the post-thaw viability and progressive motilityfor several hours as shown by thermo tolerance test andcalving rates (Klinc 2005; Klinc et al. 2007). In this AIstudy, sorted semen (2 million live sperm ⁄ straw) wasthawed and inseminated in accordance with the existingprotocols for conventional semen (thawing at 37°C for20 s; AI 12–24 h after onset of heat; semen deposition inthe uterine body or if possible without force into theipsilateral horn). Pregnancy and calving rates were equalto controls. Similar data were also obtained for sortedliquid semen stored for up to 72 h (Klinc and Rath 2007).Significant technical improvements in sperm quality aftersorting were developed using the latest laser technologyand replacing the water-cooled Argon gas laser with apulsed solid-state laser. Shorter exposure to the laserlight seems to further reduce sperm stress, and observationswith ram spermatozoa indicate increased fertilityrates (de Graaf et al. 2007c). Another stress factor is thehydrodynamic pressure. The percentage of live bull andstallion spermatozoa increased significantly when thefluid pressure was lowered from 2.07 to 2.59 mm Hg andincreased developmental rates of bovine IVF embryos(Campos-Chillon and de la Torre 2003; Suh et al. 2005).For many reasons, it may be helpful to sort conventionallyfrozen semen after thawing and refreeze thesorted samples. Such methods are under investigation.Hollinshead et al. (2004) showed for the first time thatbull semen survives an adapted protocol from ram(Hollinshead et al. 2003) employing a gradient centrifugationto separate egg yolk from the thawed samples andto enrich intact sperm prior to sorting. Maxwell et al.(2007) tested PureSperm Ò (Labotect, Go¨ ttingen, Germany)as effective gradient for high diluted, unsorted bullsperm, and in a recent study, Parrilla et al. (unpublished)showed that PureSperm and Bovipure Ò (Labotect,Go¨ ttingen, Germany) are suitable for refreezing sexedbull sperm and to produce embryos to the same extent aswith unsorted sperm from the same ejaculates.Altogether, the technical improvements made in therecent years allow for the maintenance of an acceptablestandard of bovine semen quality. Nevertheless, it is selfevidentto control the sorted sperm quality on a dailybasis. Some suggested prerequisites for sex-sorted bullsemen of optimal quality are as follows:(1) Bulls must be pre-tested and those failing withunsorted low-dose insemination should be excludedfrom their use to produce sex-sorted sperm.(2) A complete spermiogram should be made fromeach ejaculate before sorting. The test should include:macroscopical evaluation, mass movement categorization,single sperm motility estimation, evaluation ofsperm concentration and a complete morphologicalevaluation test, especially as a faster acrosome reactionis commonplace in sex-sorted sperm (Mocé et al.2006).(3) After sorting, aliquots of each batch should betested for single sperm motility, motility pattern in athermal tolerance test preferably for 6 h at 38°C,precise morphological evaluation for acrosome integrityand total morphology, FACS Analysis (FITC-PNA ⁄ Syto17 ⁄ PI; SCSA), and a general test ofmicrobiological contamination. These tests may beperformed with sorted sperm of the unwanted sex.Additionally, one straw from each batch of thewanted sex needs to be reanalysed for sorting purityand the total number of spermatozoa per straw.Ballester et al. (2007) confirmed that it is not sufficientto test semen quality directly after thawing. Incubationof the samples at 38°C revealed a reduction oflinearity, sperm viability (Seminaphtharhodafluor)and acrosome integrity.It is recommended to put at least 2 million livespermatozoa in a straw as the absolute minimum.Andersson et al. (2004, 2006) clearly showed thatmore than 2 million spermatozoa are necessary toobtain satisfactory pregnancy and calving rates.Caution must also be exercised to account for highindividual bull effects. In order to avoid losses of thehighly diluted semen, the liquid column in the strawshould be divided into a first segment containingÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag