Effect of various antioxidants and their combinations on bull semen cryopreservation

Abstract

Our objective was to evaluate the effects of adding 50 mM trehalose (TRE), 1 mM cysteine (CYS), or 400 µg catalase (CAT), individually or in combinations, to a Tris-based semen extender and determine the effects on fresh, chilled-equilibrated, and frozen-thawed bull sperm. Ejaculates from three Holstein bulls (1–3 years old) were pooled, divided into six equal portions, and put into a Tris-based extender supplemented with no additive (control), TRE, CYS, CAT, TRE + CYS, or TRE + CYS + CAT. In chilled-equilibrated semen, motility was highest in CAT but lowest in the control (P < 0.05). In thawed semen, motility was lower (P < 0.05) in CAT than in all other groups, which were not different. Based on a hypoosmotic swelling test (HOS test), TRE, CYS, and their combinations had higher (P < 0.05) percentages of sperm with an intact plasma membrane than the control or CAT groups. The TRE group had the least (P < 0.05) morphologically abnormal sperm. Plasma membrane and acrosomal integrity (PMAI) and high mitochondrial membrane potential (HMMP) values were highest in TRE and TRE + CYS and were lower (P < 0.05) in the control. Furthermore, HMMP was positively correlated with PMAI and HOS tests, but negatively correlated with major + minor abnormalities (r = 0.66, 0.242, and –0.349). In conclusion, the addition of TRE, with or without CYS, to a Tris-based semen extender improved several aspects of the frozen-thawed quality of bull semen. However, addition of CAT, by itself or in combination with other additives, did not protect bull sperm against cryopreservation-induced defects.