Telomere length in bovine sperm is related to the production of reactive oxygen species, but not to reproductive performance

Abstract

Over the last decades, selection in cattle has mainly been based on milk production rather than on reproductive efficiency. While, when applied, focus on reproduction has involved females, attention has barely been paid to males and, if so, it has only looked at classical sperm quality parameters. In effect, variables such as telomere length have been missed, despite the fact that longer telomeres have been suggested to be linked to male fertility in humans. For this reason, the present study aimed to determine the length of telomeres in bovine sperm and their relationship with a) sperm quality evaluated through the conventional spermiogram and flow cytometry, and b) bull reproductive performance. For this purpose, 29 bulls were involved in this study. Sperm telomere length was evaluated through quantitative Fluorescent In Situ Hybridization (qFISH), and sperm quality was determined at 0 h and 4 h post-thaw. Bull fertility was assessed as non-return to estrus rates after 90 days of artificial insemination. Although the mean telomere length in bovine sperm was 12.06 ± 2.75 kb, the intra-individual variability in length led us to observe three different groups of telomeres in each sperm cell: short telomeres (7.14% ± 5.79% of telomeres; 8.29 ± 2.34 kb), medium telomeres (31.03% ± 12.92% of telomeres; 16.00 ± 2.72 kb) and long telomeres (61.93% ± 18.11% of telomeres; 30.13 ± 11.35 kb). Moreover, whereas reactive oxygen species (ROS) were found to be correlated to sperm telomere length (Rs = -0.492; P= 0.007), no correlation with other sperm quality parameters was found (P > 0.05). Reproductive performance after artificial insemination was not seen to be correlated to sperm telomere length (Rs = 0.123; P= 0.520). In conclusion, this study determined, for the first time, the mean telomere length in bovine sperm and also reported that there is a high variability within each sperm cell. Yet, while telomere length was found to be correlated to ROS generation, it was not related to bull reproductive performance.

Keywords: Bull; Fertility; ROS; Sperm quality; Telomere length.