Abstract:
Semen extenders protect sperm from cold shock, osmotic stress, and alterations in membrane fluidity and permeability plus provide energy substrates for sperm metabolism. Egg yolk is one of the most common additives of animal origin that are used for semen preservation, however, it has become a suspect for facilitating the transmission of diseases. Tris-aloe vera gel have several beneficial properties, such as anti-inflammatory, antioxidant, antiviral and antibacterial features. The aim of this study was to determine the effect of Tris-aloe vera gel (TAG) extender on the quality of bull spermatozoa. In experiment 1, the effect of Tris-Aloe vera gel extender was assessed after the semen was chilled at 5 0C in a refrigerator for different storage times up to 120 hours, and frozen in liquid nitrogen at -196 0C for 5 days in experiment two. Assessment was done for morphology, motility, and viability of bull spermatozoa. Semen samples were collected from four (4) Nguni bulls with proven fertility records, aged between 6 and 8 years kept at the University of Venda Experimental Farm under intensive farming practice. Collected semen samples were pooled and diluted at a ratio of 1:5 (semen to extender) in Tris-egg yolk (TEY) as a control and TAG at three different concentration levels 12%, 16% and 20% of Aloe vera gel (AVG). In experiment one, diluted semen samples were evaluated immediately after the extension using computer aided sperm analyzer (CASA) before storage at 5 0C, followed by sperm analysis after every 24 hours for 120 hours. In experiment two, freshly collected and diluted semen samples were cryopreserved and stored at (-196 0C) in LN2 for 5 days and evaluated thereafter. The results were subjected to the analysis of variance (ANOVA) for statistical analysis using a general linear model (GLM) procedures of Minitab 19 program. Tris-egg yolk extender (TEY) with 0% aloe vera gel was used as a control. In experiment one, it was found that TEY showed consistency in keeping motility at an average of 100% (p<0.05) after 120 h of chilling semen samples. Semen samples extended in Tris-aloe vera gel had a decrease in spermatozoa motility as storage time increased. Experiment two discovered that AVG can equally be used to substitute
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egg yolk in tris-based extender and be able to cryopreserve Nguni bull semen for a period of 5 days, this is due to a fact that there was no significant difference (P<0.01) in spermatozoa progressive motility, from both TEY and TAGs post thaw. It was also found that morphological normal spermatozoa were above 80% post thaw. Semen extended in TEY shows a great deal of consistency in maintaining high spermatozoa viability throughout the chilling process.
