Empirical Investigation of Serum Metabolic Biomarker Patterns Associated with Reproductive Failure in Repeat-Breeder Friesian-Zebu Cows in Oyo State, South West Nigeria

Repeat breeding in cattle constitutes a significant reproductive failure syndrome with multifactorial aetiologies including uterine pathology, hormonal dysregulation, and metabolic disease. Despite its economic importance in Nigerian smallholder and commercial dairy systems, empirical metabolic biomarker data from repeat-breeder cows in South West Nigeria are absent from current literature. This study investigated serum metabolic biomarker patterns in repeat-breeder Friesian-Zebu crossbred cows in Oyo State, comparing them with normally cycling cows that conceived on first insemination. Eighty cows designated as repeat breeders after three or more failed consecutive inseminations and forty normally cycling control cows were enrolled. Serum insulin-like growth factor-1, glucose, non-esterified fatty acids, beta-hydroxybutyrate, progesterone, oestradiol, and thyroid hormones were measured at breeding and at day eighteen and day twenty-five post-insemination. Repeat breeders had significantly lower serum insulin-like growth factor-1 and progesterone concentrations at the time of breeding compared to controls, alongside elevated non-esterified fatty acids, consistent with persistent negative energy balance despite apparent clinical normality. Thyroid hormone profiles were marginally depressed in repeat breeders, suggesting a mild functional hypothyroid-like state. Logistic regression identified non-esterified fatty acid concentration at breeding as the strongest independent predictor of repeat breeding status. These empirical findings identify actionable metabolic targets for improving reproductive performance in South West Nigerian dairy herds. Keywords: repeat breeding, serum metabolites, non-esterified fatty acids, reproductive failure, Oyo State.