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.

Highlights

  • Bull semen is frequently cryopreserved, there are many deleterious effects on frozen-thawed sperm [1], including decreases in motility, DNA and plasma membrane integrity, and sperm mitochondrial membrane potential, plus increased lipid peroxidation [2,3,4]

  • For Plasma membrane and acrosomal integrity (PMAI) and high mitochondrial membrane potential (HMMP), values were highest in TRE and TRE + CYS and were lowest (P < 0.05) in the control group (Table 2)

  • HMMP was positively correlated with PMAI (r = 0.66; P < 0.01) and hypoosmotic swelling (HOS) test (r = 0.342; P < 0.05) and negatively correlated with major + minor abnormalities (r = –0.349, P < 0.05; Table 4)

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Summary

Introduction

Bull semen is frequently cryopreserved, there are many deleterious effects on frozen-thawed sperm [1], including decreases in motility, DNA and plasma membrane integrity, and sperm mitochondrial membrane potential, plus increased lipid peroxidation [2,3,4]. As semen extender substantially affects the quality of frozen-thawed sperm [5], there is a strong impetus to continue to improve extenders and freezing methods [6]. Due to their lipid composition and fatty acid ratios, sperm membranes are very sensitive to temperature changes during cooling and freezing [7], with much potential for oxidative stress and cell damage [8]. The disaccharide trehalose (TRE) apparently potentiated activities of catalase, superoxide dismutase, and glutathione, thereby protecting sperm membranes from oxidative damage and lipid peroxidation [11]. Cysteine (CYS) stimulates glutathione synthesis and decreased oxidative stress [19], improving bull sperm membrane integrity [9] and buck sperm motility [20]

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