Thyroxine, Triiodothyronine and Reverse-Triiodothyronine Concentrations in Blood Plasma in Relation to Lactational Stage, Milk Yield, Energy and Dietary Protein Intake in Estonian Dairy Cows

摘要: Average levels of thyroxine (T4), triiodothyronine (T3) and reverse-triiodothyronine (rT3) in blood plasma 159 Estonian Red Black White cows were 55.2 nmol/L, 1.78 nmol/L 0.25 respectively. Animals grouped according to stage lactation. The T4 level was significantly lower during the early lactation (45.1 nmol/L), compared with later stages, but increased as progressed (late lactation–56.7, dry 64.3 nmol/L). T3 higher at late (1.93 nmol/L) (1.71 rT3 showed a trend similar that found for (lowest concentration lactation, 0.19; highest period, 0.33; 0.24 Levels all thyroid hormones negatively related daily milk yield (T4− r = −.51, − −.47, calculated index rT3*T3*T4− −.52, p<.0001; −.32, p<.01). Plasma hormone concentrations affected by energy dietary protein intake. Differences between 2 breeds summer winter holding periods cows, which could be explained differences feeding yield. It is suggested maintaining low may one dairy cow’s mechanisms reducing metabolic demand.