Sammendrag
Intracytoplasmic sperm injection (ICSI) is an important reproductive technology that passes over some crucial steps of the fertilization process like capacitation, acrosomal reaction, and membrane fusion. The inadequacy of ICSI in bovine species is due to the incapability of sperm decondensation and pronucleus formation after injecting the sperm cell into the egg cytoplasm. Thus, the present study aimed to analyze the decondensation level of sperm heads by applying different concentrations of glutathione (GSH) and dithiothreitol (DTT) to sperm samples from four bulls. Additionally, 1 mM of DTT was used to treat semen samples at two different ages (14 months and 20 months) from five bulls, to detect the effect of bull and age differences. Besides, the analysis level of free-thiol groups by staining with mBBr dye was established as a new protocol. The semen quality parameters: progressive and hyperactive motility, average head area, viability, and acrosomal integrity, free-thiol groups, DNA integrity were analyzed. The data analysis was done by using the general linear mixed model (GLMM) and by using the Kruskal Wallis test for data that did not fit the model. As the results from this study indicate, the treatment with DTT increased the progressive and hyperactive motility of the sperm cells. Progressive motility and average head area had no significant variation between the bulls and the two age groups. The random effect intercept value (0.1714) of hyperactive motility showed substantial differences across the bulls. Even though there was no significant difference compared to the control group, the rate of the acrosome-reacted sperm cell was higher after the 1 mM DTT treatment. Compared to the control group, the level of free thiols showed significant variation at 14 months (p = 0.0026) and 20 months (p < 0.0001) age groups. The DFI and HDS parameters were significantly affected by DTT treatment. The 1 mM DTT treatment effect on the DFI parameter was higher for 14-month age groups, while the HDS parameter showed a higher impact on 20-month age groups. The HDS showed a detectable variance between bulls with a random effect intercept value of 0.159. Consequently, expanding the experimental size and applying different concentrations of the DTT and GSH chemicals on various age groups and bulls could create a procedure with an optimal concentration level of the treatment for sperm decondensation before the ICSI procedure.