Effects of anti-oxidant additives on microscopic and oxidative parameters of Angora goat semen following the freeze–thawing process

The anti-oxidant system of reduced glutathione (GSH), glutathione peroxidase (GSH-PX), catalase (CAT), and superoxide dismutase (SOD) has been described as a defense functioning mechanism against lipid peroxidation (LPO) in semen, and is important in maintaining sperm motility and viability. This anti-oxidant capacity of sperm cells may be insufficient in preventing LPO during the freeze–thawing process. The aim of this study was thus to determine the influence of varying doses of anti-oxidant additives on standard semen parameters, lipid peroxidation and anti-oxidant activities after the freeze–thawing of goat semen. Ejaculate samples (artificial vagina) obtained from 4 mature Angora goats were evaluated and pooled at 37 °C. The semen samples diluted with a Tris-based extender, containing taurine (25, 50, 75 mM), trehalose (25, 50, 75 mM), and cysteine (5, 10, 15 mM), and an extender containing no anti-oxidant additives (control) were again evaluated. Diluted semen was cooled down to 5 °C and frozen in 0.25 ml French straws, prior to being stored in liquid nitrogen. Frozen straws were thawed in a water bath (37 °C) for 30 s for microscopic sperm evaluation. Upon evaluation of parameters for semen quality, the use of a Tris-based extender supplemented with anti-oxidant additives was found to cause no significant improvement in sperm mortality, when compared to the controls. Increasing doses of taurine and trehalose decreased (P < 0.05) the sperm motility following the freeze–thawing of the goat semen. In biochemical assays, the application of taurine (75 mM) produced the lowest level of malondialdehyde (MDA) (4.46 ± 0.31 nmol/ml), compared to the controls (P < 0.001). Lower GSH levels were higher in the groups in which cysteine was included at 10 and 15 mM (3.27 ± 0.11 and 3.45 ± 0.28 nmol/ml) – compared to the group which received 5 mM cysteine, as well as the controls (2.27 ± 0.08 and 2.50 ± 0.08 nmol/ml respectively, P < 0.001). Compared to the controls, taurine at a concentration of 25 and 75 mM, and increasing doses (50 and 75 mM) of trehalose, significantly increased the GSH-PX activity (P < 0.01). The maintenance of CAT activity was demonstrated to be higher with the addition of 10 and 15 mM cysteine, compared to the other groups (P < 0.001). Vitamin A (VitA) levels were significantly higher, compared to the controls (267.34 ± 9.68 mg/dl and 267.34 ± 9.68 mg/dl, respectively), when 25 mM taurine (329.61 ± 6.35 mg/dl) and 10 mM (318.64 ± 6.34 mg/dl) cysteine was added to the extender (P < 0.001). The results of this study provide a new approach to the cryopreservation of Angora goat semen and could contribute to the improvement of this technology in the goat industry.