Diurnal Variation in Blood Cortisol Levels in Cattle Managed Intensively in Oyo State

Cortisol, the primary glucocorticoid in cattle, exhibits well-described diurnal rhythmicity in temperate breeds but patterns in Zebu and crossbred cattle maintained under intensive management in West Africa have received limited investigation. Understanding cortisol rhythmicity is relevant to animal welfare assessment, optimal timing of stress-inducing husbandry procedures, and disease monitoring. This study characterised diurnal variation in serum cortisol concentrations in White Fulani and Friesian crossbred cattle managed intensively at a livestock farm in Ibadan, Oyo State, South West Nigeria. Thirty cattle were sampled at six time points: 06:00, 09:00, 12:00, 15:00, 18:00, and 21:00 hours over two consecutive days. Blood was collected rapidly by jugular venepuncture to minimise sampling-induced cortisol release. Cortisol was measured by enzyme-linked immunosorbent assay. White Fulani cattle exhibited a bimodal cortisol pattern with peaks at 06:00 and 18:00 hours, while Friesian crossbreds showed a unimodal morning peak. Mean cortisol was significantly higher at 06:00 hours in both breeds. Afternoon cortisol was significantly elevated on days with maximum ambient temperature above 35 degrees Celsius. These findings provide insight into cortisol dynamics in Nigerian cattle and suggest that routine husbandry procedures such as vaccination and dehorning should ideally be scheduled between 09:00 and 12:00 hours when cortisol is declining, to minimise compounding stress effects. Keywords: cortisol, diurnal variation, cattle, Ibadan, stress.