Thyroid Function and Its Correlation with Milk Production in Friesian Crossbred Cows in Ogun State

Thyroid hormones, principally thyroxine and triiodothyronine, regulate basal metabolic rate and are closely associated with productive performance in dairy cattle. In high-producing Friesian crossbred cows managed under intensive conditions in Ogun State, South West Nigeria, thyroid dysfunction may contribute to suboptimal milk production and metabolic imbalances. This study investigated the relationship between circulating thyroid hormone concentrations and daily milk yield in Friesian crossbred cows at a peri-urban dairy farm in Abeokuta. Fifty cows at different lactation stages were enrolled. Blood samples were collected monthly over a four-month period, and serum total thyroxine and triiodothyronine were quantified by ELISA. Daily milk yield was recorded by weighing milk at each milking session. Body condition score and dry matter intake were concurrently recorded. Correlation analysis was performed between thyroid hormone levels and production parameters at each time point. Total thyroxine concentrations ranged from 38.4 to 68.2 nmol/L and showed a statistically significant positive correlation with daily milk yield at all time points. Cows in early lactation had the highest thyroxine concentrations, declining through mid to late lactation. Triiodothyronine showed a weaker but still significant correlation with milk yield. Cows with body condition score below 2.5 had the lowest thyroid hormone concentrations and poorest milk yields. These findings suggest that thyroid hormones may serve as markers of metabolic adequacy and productive potential in Nigerian dairy cattle and merit consideration in nutritional and health management programmes. Keywords: thyroid hormones, milk production, Friesian, Ogun State, thyroxine.