Bull Fertility and Epigenetics: Exploring Influences Beyond Genetics

Genetics explains only ~15% of male infertility; a cattle review argues epigenetic marks fill the gap — and pass across generations

Journal: Reproduction in Domestic Animals | Published: 2026-03 | Type: Narrative Review | PMID: 41757565 Authors: Sethi M, Mohanty TK, Shah N, Bhakat M, Kumar N, Baithalu RK, Swain D — ICAR Artificial Breeding Research Centre and affiliated Indian agricultural universities Funding/COI: Not disclosed

Summary

Genomic research has hit a wall: genetics accounts for no more than 15% of male infertility cases, leaving the vast majority unexplained by DNA sequence alone. This narrative review argues that epigenetic mechanisms — DNA methylation, histone modifications, and non-coding RNAs — explain part of the remaining variance in bull fertility, and that those marks can be set or disrupted by the bull's mother's nutrition, his own postnatal diet, stress, housing, and temperature. All of this is in cattle, studied for artificial insemination efficiency. Human applicability is inferred, not demonstrated.

Claims

• Genetic factors explain no more than 15% of male infertility cases across species
• Three epigenetic mechanisms differ measurably between high- and low-fertility bulls: DNA methylation patterns, histone modification profiles, and non-coding RNA expression
• Maternal nutrition during gestation influences the sperm epigenome of male offspring
• Postnatal environmental exposures — diet, stress, housing conditions, temperature — alter bull calf sperm epigenomes
• These epigenetic modifications show transgenerational heritability, meaning they propagate to subsequent generations
• Epigenetic biomarkers are proposed as a potential screening tool to rank bulls by predicted fertility before deployment in artificial insemination programs

Study Quality

This is a narrative review, not a systematic one. There is no PRISMA flow chart, no defined search strategy, no inclusion/exclusion criteria, and no assessment of the quality of individual studies cited. The authors select and synthesize literature according to their own judgment, which introduces the full weight of selection bias. Claims about effect sizes, mechanisms, and transgenerational inheritance are presented as established fact without meta-analytic support.

The subject matter is cattle reproductive biology, studied in the context of dairy industry artificial insemination programs — a setting with strong economic incentives to predict bull fertility accurately. The mechanisms discussed (DNA methylation, histone marks, ncRNA) are real and well-characterized in the broader epigenetics literature. However, the review makes no systematic attempt to quantify effect sizes, evaluate conflicting evidence, or distinguish what is experimentally demonstrated in bulls from what is extrapolated from rodent or human research.

Red Flags

• Narrative review methodology — no systematic search, no quality appraisal of cited studies
• All primary subject matter is bovine; human relevance is implied, not evidenced
• Funding source not disclosed despite institutional affiliations with organizations that benefit commercially from improved bull fertility prediction
• No conflict of interest statement
• The "15% of infertility explained by genetics" figure is cited without a source in the abstract — the primary literature behind this claim is unverifiable from the abstract alone
• Transgenerational epigenetic inheritance in mammals is mechanistically contested; the review treats it as settled
• No original data; the paper contributes synthesis, not new findings

Strengths

• Covers all three main epigenetic regulatory layers (methylation, histone marks, ncRNA) in one place
• Practical framing around artificial insemination screening gives the biomarker claims an actionable context
• Raises a legitimate and underexplored question: if genetics explains only 15% of infertility variance, what explains the rest?
• The transgenerational angle — maternal diet affecting offspring sperm epigenome — is a mechanistically plausible hypothesis with supporting rodent literature

Verdict

A useful orientation piece for anyone new to epigenetics in male fertility, but read it as a perspective, not evidence. The 15% genetic explanation figure is striking and worth following up in primary literature, but this review provides no systematic basis for evaluating whether epigenetic biomarkers can actually predict human male fertility. The bovine focus is not a disqualifier — cattle epigenomics research is real and mechanistically informative — but the leap to human clinical relevance is taken without justification. The missing funding and COI disclosures from an institution whose core mission is bull semen quality is a gap worth noting.