Influence of Coconut Powder Water-Based Conservation Medium (APC-102c) for Maintaining Mitochondrial Activity of Cryopreserved Ram Sperm

Abstract

Background:  Semen extenders are required to protect and preserve semen, and the development of suitable extenders is key for artificial insemination. Although the use of Tris-based diluent is widespread, new diluents such as powdered coconut water have been developed for better sperm protection. One way to evaluate the effectiveness of diluents is through microscopic analyses that evaluate sperm motility, vigor, and concentration. However, these analyses are limited, and may not provide accurate results. New evaluation techniques have been studied, and one of the tests that can be used to add reliability to these analyses is mitochondrial activity evaluation, which can sum all the parameters, and provide a more accurate evaluation. Thus, the present study aimed to evaluate the efficacy of ACP-102c in cryopreserved ram semen.

Materials, Methods & Results: Five semen samples were collected from two ram breeders using artificial vagina (n = 10). Each ejaculate was divided into the following two treatments: T1 - ACP-102c + 20% egg yolk + 7% glycerol and T2 - TRIS + 20% egg yolk + 7% glycerol. Extended semen samples were then packed in 0.5 mL plastic straws, subjected through the refrigeration curve up to 4°C (0.35° C/min), and equilibrated for 2 h at 4°C. Subsequently, the straws were placed at 4 cm above liquid nitrogen level (-60°C) for 15 min, immersed, and then finally stored in the liquid nitrogen at -196°C. Both fresh and thawed samples were evaluated for total and progressive sperm motility using conventional microscopy (40x), and the same evaluator on each occasion. For plasma membrane integrity (IMP), the smear staining technique with the Eosin-Nigrosin staining was used; 200 sperms were counted and classified as whole (unstained) and unhealthy (stained). Mitochondrial activity was evaluated using a cytochemical technique based on the oxidation of 3,3'-diaminobenzidine (DAB); 200 sperms were counted, and classified into four classes (I, II, III, and IV) according to the degree of coloration of the intermediate part. Fresh semen showed no significant difference (P > 0.05) between treatments with respect to motility parameters; however, T2 showed significantly inferior results regarding plasma membrane integrity. After thawing, T2 was significantly higher in sperm motility parameters compared to T1. The mitochondrial activity and plasma membrane integrity parameters did not show any significant difference between the treatments.

Discussion: The TRIS-based diluent showed higher motility values than ACP-102c; however, motility rates in ACP-102c diluent, although lower, are considered satisfactory for insemination, which requires semen with minimal progressive motility of 30%. Notably, the cryopreservation protocol used in this study is the standard for TRIS-based diluent, and it is known that the optimal rate of refrigeration and cryopreservation may differ according to the composition of the storage medium; therefore, we may assume that the protocol used is not yet appropriate for the ACP-102c diluent, and further studies are required. IMP is an essential attribute for fertilization, and cryopreservation can affect the plasma membrane as observed in this study. Cryopreserved semen reduced the percentage of class I mitochondrial reaction sperms in both treatments, demonstrating that cryopreservation affects the mitochondrial activity of the intermediate portion of the sperm; however, there was no difference between treatments in thawed semen. Thus, we concluded that the ACP-102c conservation medium maintains seminal quality after thawing, and it can be used in artificial insemination processes.