Building a bovine blood DNA methylation epimap related to disease phenotypes

Epigenetic variations, particularly in response to environmental factors, play a crucial role in shaping immune identity and function in hematopoietic cells. This study investigates interindividual differences in DNA methylation among dairy cows, with the aim of enhancing our understanding of the adaptive capacity essential for sustainable animal production. We conducted whole-genome sequencing and DNA methylation analysis using enzymatic methyl-seq on whole blood from 60 Holstein cows. The study included five phenotype groups: mastitis, lameness, infertility, metabolic disorders and healthy controls.

Among the 50 million CpG sites, 5.1% were identified as variable methylated cytosines (VMCs) and 94.9% as conserved methylated cytosines (CMCs). VMCs displayed variability in distal promoter regions, suggesting potential plasticity in the associated genes, while CMCs exhibited a bimodal methylation pattern near the transcription start site, indicative of tissue-specific functions. Notably, we identified motif enrichments related to genes potentially expressed in blood. An age-related analysis revealed a 1.4% faster decline in CMCs methylation compared to VMCs. Additionally, disease risk assessment may be achievable using as few as 586 methylation biomarkers, which could be used to select which cows to keep in the herd for additional lactation.

Our results suggest a dual role for VMCs and CMCs: while the stability of conserved sites is potentially associated with essential functions in cell development and homeostasis, variable sites may be involved in dynamically regulating gene transcription in response to internal or external stimuli. These insights underscore the epigenome's role in immune regulation and adaptive resilience in cattle.