Sperm selection techniques are needed to separate spermatozoa from seminal plasma and extender for in vitro fertilization (IVF) and to improve sperm quality for a range of assisted reproduction techniques. Apart from sperm washing, which removes some but not all of the seminal plasma, the selection techniques that are currently used are mainly swim-up and colloid centrifugation; filtration through Sephadex columns or glass wool is seldom used in the field. Although swimup can be used to prepare

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... sperm samples for IVF, the low recovery rate and lack of selection for sperm quality other than motility make this technique ineffective for routine use. Colloid centrifugation is used to prepare semen for all types of assisted reproduction. The method has been scaled-up for voluminous ejaculates e.g. from stallion and boar, and scaled-down to accommodate small volumes of thawed semen (e.g. from bull). Sperm quality and fertility are improved, as shown in laboratory assays and in various fertility trials. Some normal spermatozoa are lost during the selection process but overall the advantages of improved longevity and fertility in the selected spermatozoa outweigh the disadvantages. Since spermatozoa are separated from bacteria in the ejaculate, it may be possible to reduce antibiotic usage in semen extenders. New applications of colloid centrifugation include extracting camelid spermatozoa from viscous seminal plasma, selecting spermatozoa with condensed chromatin (i.e. with fewer free thiols), and using the number of spermatozoa passing through the colloid as a diagnostic tool to indicate male fertility. Colleoni S, Lagutina I, Rodriguez-Martinez H, Lazzari G, Galli C, Morrell JM. 2011. New techniques for selecting spermatozoa for equine assisted reproduction. J Equine Vet Sci, 31:536-541. Cuervo-Arango J, Aguilar J, Newcombe JR. 2009. Effect of type of semen, time of insemination relative to ovulation and embryo transfer on early equine embryonic vesicle growth as determined by ultrasound. Theriogenology, 71:1267-1275. de Graaf SP, Leahy T, Marti J, Evans G, Maxwell, WMC. 2008. Application of seminal plasma in sexsorting and sperm cryopreservation. Theriogenology, 70:1360-1363. Diskin MG, Morris DG. 2008. Embryonic and early foetal losses in cattle and other ruminants. Reprod Domest Anim, 43(suppl. 2):260-267. Evenson DP. 2016. The Sperm Chromatin Structure Assay (SCSA®) and other sperm DNA fragmentation tests for evaluation of sperm nuclear DNA integrity as related to fertility. Anim Reprod Sci, 169:56-75. Goodla L, Morrell JM, Yusnizar Y, Stålhammar H, Johannisson A. 2014. Quality of bull spermatozoa after preparation by single layer centrifugation. J Dairy Sci, 97:2204-2212. Hoogewijs M, Morrell JM, Van Soom A, Govaere J, Johannisson A, Piepers P, De Schauwer C, de Kruif A, De Vliegher S. 2011. Sperm selection using single layer centrifugation prior to cryopreservation can increase post thaw sperm quality in stallions. Equine Vet J, 43(suppl. 40):35-41. Hoogewijs M, Piepers S, Govaere J, De Schauwer C, de Kruif, A Morrell JM. 2012. Sperm longevity following pre-freeze sperm selection. J Equine Vet Sci, 32:489. doi: http://dx.