Epigenetic Regulation of Stress Response Genes in Working Animals Under Chronic Load-Bearing Conditions in North East Nigeria

Chronic physical stress induces durable epigenetic modifications including DNA methylation and histone modification at stress response gene loci, potentially programming long-term changes in neuroendocrine and immune function. Working animals including donkeys, horses, and cattle used for transport and agricultural draught in Borno, Adamawa, and Taraba states in North East Nigeria experience sustained chronic physical loading under nutritionally challenging conditions. This study investigated epigenetic regulation of key stress response genes in working donkeys, horses, and cattle from North East Nigeria compared with matched non-working controls, employing genome-wide DNA methylation sequencing and targeted histone modification profiling. Working animals were recruited from veterinary field visits in Maiduguri, Yola, and Jalingo, with 20 working and 10 non-working individuals per species. Peripheral blood mononuclear cells were isolated and subjected to reduced representation bisulphite sequencing for genome-wide CpG methylation profiling. Chromatin immunoprecipitation sequencing for H3K4me3 and H3K27me3 marks was performed on selected target regions. Differentially methylated regions were identified by DESeq2-based analysis and annotated to gene ontology biological processes. The glucocorticoid receptor gene NR3C1 promoter region showed significant hypermethylation in working donkeys and horses relative to controls, associated with reduced glucocorticoid receptor mRNA expression and attenuated cortisol suppression by dexamethasone. FKBP5 and CRHR1 also showed species-specific methylation changes. Histone marks at immune gene loci were significantly altered in all working species. These findings establish proof-of-concept for epigenetic reprogramming in Nigerian working animals and open new directions for welfare biomarker development and therapeutic epigenetic modulation. Keywords: epigenetics, DNA methylation, stress response, working animals, North East Nigeria.