Evaluation of Serum Thyroid Function Indices as Indicators of Energy Balance Status in Transition Zebu Cows in Borno State, North East Nigeria

Thyroid hormones serve as integrative metabolic regulators whose concentrations reflect systemic energy balance, yet their utility as indirect indicators of negative energy balance in transition Zebu cattle under the semi-arid conditions of North East Nigeria has not been empirically investigated. This study evaluated serum triiodothyronine, thyroxine, and thyroid-stimulating hormone in relation to direct energy balance markers in transition Zebu cows in Borno State. Eighty cows were monitored from three weeks prepartum through five weeks postpartum with biweekly blood sampling for thyroid hormones, non-esterified fatty acids, beta-hydroxybutyrate, glucose, and insulin. Energy balance was calculated from daily feed intake and milk energy output records. Serum triiodothyronine declined significantly from prepartum values in the first two weeks postpartum in all cows, with the most pronounced depression in cows experiencing the greatest calculated negative energy balance. Thyroxine showed a parallel but less pronounced trend. Serum thyroid-stimulating hormone remained stable throughout, suggesting central euthyroidism with peripheral downregulation of hormone conversion as a metabolic adaptation to energy deficit. Correlation analysis confirmed a significant positive relationship between serum triiodothyronine and calculated energy balance scores. These empirical findings support the potential of serum triiodothyronine as an accessible indirect energy balance indicator in transition Zebu cows, supplementing direct non-esterified fatty acid measurements in resource-limited North East Nigerian dairy settings. Keywords: thyroid hormones, energy balance, transition cows, negative energy balance, Borno State.