Browsing by Author "Paul, Tristen Lee"

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    A meta-analysis of the role of subpopulation analysis in the qualification and quantification of sperm sample quality, and the relationship with male fertility
    (Stellenbosch : Stellenbosch University, 2021-04) Paul, Tristen Lee; Lambrechts, Helet; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Given the predicted increase in the world population by 2050, the expected demand for animal products places increasing pressure on livestock farmers to farm as sustainable and cost-efficient as possible, taking environmental challenges such as global warming into account. The identification and selection of animals that have a superior ability to cope with and produce under conditions that are challenging, will assist livestock producers to contribute directly to food security. The development and application of assisted reproductive technologies (ART’s) such as artificial insemination (AI) and in vitro embryo production (IVEP) and transfer, offers livestock producers the opportunity to overcome limitations such as the seasonal nature of reproduction in certain species, and long generation intervals. The successful application of ART’s, however, requires the identification of quality spermatozoa that will be able to participate in fertilization. One of the limitations of current sperm sample evaluation protocols, is the inherent subjective nature of the evaluation protocols, which is largely due to the use of trained technicians, which in turn dictates that a certain level of experience is also required. This lead to the development of computer-assisted sperm analysis (CASA) systems, with the aim to overcome the limitation of the subjective nature of sperm sample evaluation protocols, and thus biased values obtained. Sperm samples, whether ejaculate or epididymal in origin, naturally are characterized by a degree of heterogeneity, which contributed to the development of a sperm subpopulation approach to quantify sperm sample quality, and the fertilizing ability of spermatozoa in said samples. Knowledge of sperm fertilizing ability is important in determining male fertility under natural mating conditions (field fertility) or for use in ART’s such as IVEP. A meta-analysis was conducted to establish and quantify the use of sperm subpopulations to quantify male fertility by doing an in-depth analysis of existing peer-reviewed publications using specific criteria. All available web-based databases were used for this search, and publications that met all the selection criteria were thoroughly explored. Datasets for CASA-generated motility- and sperm head morphometry parameters were generated, and subjected to statistical analyses using a mode approach, where species, sperm subpopulation, type of CASA system used, and type of medium used, were considered as fixed effects. Findings from this study highlighted the inconsistency between studies, as well as lack of an identified link between sperm subpopulations and male fertility, whether under field conditions or for use of spermatozoa in ART’s. A lack of consensus amongst authors regarding subpopulation classification, especially in terms of the pre-determined cut-off values and thus the descriptive categories that are used to classify and describe sperm clusters, whether it be for sperm motility (i.e. fast, medium, and slow) or sperm head morphometry (i.e. large, short, round, elliptical, etc.), was reported. Given the multi-factorial nature of fertilization, standardization between research group and laboratories in terms of cut-off values for sperm subpopulations is warranted to allow for the establishment of whether a sperm subpopulation approach in quantifying sperm fertilising ability is firstly feasible, and secondly whether CASA can be incorporated in livestock and wildlife management programs as a management tool. It is recommended that future studies include both sperm motility and sperm head morphometry in the study designs, as this will provide a more accurate indication of sperm fertilising potential, and thus a male´s fertility. Additionally, studies should report more detail on sample preparation, processing, and imaging, which will allow improved quantification of results and standardization between laboratories. Furthermore, there is under-representation for various species, and more studies are warranted to allow for the development of standardized species-specific protocols, which in turn can lead to the establishment of reproductive indices for animals, under field conditions and/or for use of their gametes in ART’s, which in turn will assist livestock and wildlife managers to select species with an ability to cope under certain production conditions. Selection of wildlife species that can cope with challenging environmental conditions, will assist in maintaining of ecosystem stability, and also allow for the use of spermatozoa obtained from such animals, to be used in ART’s in the establishment of genome resource banks for said species.