Thyroid hormones and cortisol in dairy cows
1993
Tiirats, E.
Total thyroxine, total triiodothyronine and cortisol in blood plasma of 240 cows were assayed by radioimmunoassay during one year and correlated with a stage of lactation, season, daily milk yield and energy content in feed. The average level of thyroxine was 38.1 nmol/l, triiodothyronine 2,56 nmol/L and cortisol 23,9 nmol/L. No differences of thyroxine and triiodothyronine concentrations between different genotypes were found. The triiodothyronine level was higher at the late stage of lactation and was similarly low both at the early stage of lactation and in dry cows. The cortisol average concentrations of different stages of lactation were similar. This study suggests a close relationship between the thyroxine level in plasma and maximum secretion of milk and stage of lactation (incl. dry period)
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