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Cryopreserved Sperm quality in young Brangus bulls raised on pasture and supplemented with vitamin E
Vitamin E (or tochopherol) is a fat-soluble antioxidant that inhibits propagation of chain reactions induced by reactive oxygen (ROS) species in biological membranes , being an important defense mechanism against oxidative damage caused to sperm membrane , and reducing lipid peroxidation of membranes . The objective of this study was to evaluate semen characteristics and semen quality after freezing of young bulls raised on pasture and supplemented with vitamin E (α-tochopherol acetate). Sixteen Brangus bulls with 24 months of average age and 462.2 kg of body weight mean, were randomly assigned to two treatments. Treatments were: control group (CG, without supplementation) and group supplemented with vitamin E (GE - 400 IU of vitamin E/day added into concentrate). Each group was kept in separate paddocks formed by Panicum maximum cv. Mombaça and received 4.5 kg concentrate/animal/day. Animals received vitamin E supplementation for 60 days. Semen was collected by electroejaculation and diluted in TRIS – egg -yolk citrate extender with 4% of glycerol and were manually frozen. Cryopreserved semen was thawed in a water bath at 360C for 30 seconds. Immediately after thawing were evaluated sperm motility (percentage of mobile sperm), sperm vigor (intensity of motility, 1-5), sperm viability (percentage of live sperm), acrosome integrity (percentage of acrosome membrane integrity), sperm integrity (percentage of sperm with membrane integrity), and occurrence of acrosome reaction (percentage). The experiment was a completely randomized design with repeated measures and data were analyzed by ANOVA with a significance level of 5 %. Supplementation with vitamin E improved the sperm viability (p = 0.0225) post-thaw (76.83 ± 2.07 vs. 81.91 ± 2.56). None effects of supplementation (p > 0.05) was observed in other traits. Based on parameters evaluated and results obtained from supplemented animals, it is concluded that this level of supplementation was beneficial for semen subjected to cryopreservation process indicating a better protection of the sperm membrane to membrane damage caused by freezing semen, justified by increased percentage of viable cells found in the supplemented group compared with control group.
Keywords: cryopreservation, oxidative stress, sperm viability