Bull Fertility and Epigenetics: Exploring Influences Beyond Genetics

Infertility has been a concern throughout the ages and is still a significant problem in several species, including human beings and farm animals. Many research projects have focused on exploring the genetic basis of male infertility, but thus far, they have been able to explain not more than 15% of infertile cases. Therefore, much remains to be understood, and we need to involve several other approaches to fully understand the aetiology of male infertility. One such promising approach is epigenetics, which has the potential to explain the aetiology of numerous disorders partially. Epigenetics is a discipline that studies heritable changes in gene expression that do not involve altering the DNA sequence. The main epigenetic mechanisms include the well-understood phenomenon of DNA methylation, histone modifications and regulation by non-coding RNAs, a mode of regulation identified relatively recently and an area of intensive ongoing investigation. In cattle and especially dairy breeds, where bull semen is widely used for artificial insemination (AI), several selection and breeding practices may interfere with the proper establishment of the sperm epigenome. The future bull progeny's sperm epigenome may be influenced by the mother's nutrition, potentially affecting future fertility. The bull calf's postnatal diet and environment, including stress, housing conditions and temperature, affect the sperm epigenome. These epigenetic modifications have a transgenerational effect, meaning they affect the fertility of subsequent generations. It has been observed that epigenetic modifications, such as DNA methylation, histone modifications and non-coding RNAs, differ between high- and low-fertility bulls. Prediction of these epigenetic biomarkers may therefore provide a new method for differentiating between high- and low-fertility bulls.