38 Ram sperm longevity after cryopreservation in extender containing L-carnitine

Abstract

The cryopreservation process causes oxidative stress to the sperm cell, and the addition of antioxidants to the extender for semen freezing helps sperm protection. This study assessed the effect of L-carnitine (LC) concentrations (0, 5, or 10 mM LC) on two ram semen extenders (Tris-egg yolk or the commercial optiXcell IMV medium (IMV Technologies)) for semen cryopreservation. Four Santa Inês rams were used during the breeding season. After semen collection, macroscopic and microscopic evaluations were performed, and a pool of semen was formed. The semen was diluted, and the final concentration was 100 × 10⁶ per 0.25-mL straw. Cryopreservation was performed with a cooling rate of 0.25°C min⁻¹ until 5°C, and the freezing rate used was 20°C min⁻¹ from 5 to −120°C. After the freezing-thawing process and throughout incubation (38°C in 5% CO₂) in Fert-Tyrode's albumin lactate pyruvate medium, every 1 h for up to 3 h, several parameters were evaluated: sperm kinetics, hypo-osmotic test, plasma membrane integrity, capacitation status, and lipid peroxidation level. We did not find any protective effect of LC on plasma membrane integrity, hypo-osmotic test, and capacitation status. The sperm kinetics values throughout incubation showed that Tris extender promoted better indices of staight-line velocity, linearity, wobble, and straightness than IMV extender along incubation, regardless of the presence of LC. There were no benefits of the LC addition throughout the incubation, and 10 mM was deleterious to few parameters (amplitude of lateral head displacement, linearity, and wobble) compared with the control (0 mM) in the Tris extender group. The plasma membrane integrity analysis revealed no differences (P > 0.05) among the groups. The average number of intact cells (hypo-osmotic) was higher in Tris extender groups supplemented with 10 mM LC at 1 h and 5 mM LC at 2 h compared to the respective extender IMV groups. Regarding capacitation status, the Tris 5 mM LC group had more acrosome-reacted cells when compared with the IMV 5 mM LC group at 2 h. At 3 h, the percentage of acrosome-reacted cells was higher in the Tris 0-mM group when compared with the IMV 0-mM group. Regardless the presence of LC, IMV had higher (P < 0.05) lipoperoxidation than the Tris treatments. In conclusion, LC supplementation in semen extender had no beneficial effect on freezing-thawing ram sperm and throughout incubation for up to 3 h, with no difference in each time point evaluated. Under the conditions of this study, the use of Tris extender was superior to IMV extender for ram sperm.

Financial support for this work came from the Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (Young Scientist Program of Our State; E-26/203.168/2017).