Thyroxine and triiodothyronine concentrations during lactation in dairy cows

Abstract

The present study was conducted to investigate the behaviour of thyroid hormones in association with milk yield in early, at peak and in mid-lactation in dairy cows. Blood samples obtained from 45 lactating dairy cows in various stages of lactation were analysed by radioimmunoassay for thyroxine (T4) and triiodothyronine (T3). Milk yield and serum concentrations of T4 and T3 were recorded for early, mid- and peak stage of lactation. Thyroxine and triiodothyronine both exhibited similar profiles in response to stage of lactation. Concentrations in early and at peak lactation were significantly (P < 0.001) lower than in mid-lactation, when milk production markedly decreased. (© Elsevier / Inra).