Thyroid hormones, urea and ketoplastic aminoacids in blood plasma of lactating cows
1994
Tiirats, T. (Estonian Agricultural University, Tartu (Estonia))
Total thyroxine, total triiodothyronine, urea and some ketoplastic aminoacids (Lys, Phc Tyr, Leu, Ile) of plasma were estimated in 320 lactating cows during a two years study period. The feed samples were analysed for diet energy and digestive protein content. These all have been compared with calculated requirements. The daily milk yield was taken in account as well. The cows under study were divided into three groups as follows: low energy diets, normal energy supply and high energy. The higher energy overfeeding was accompanied by higher T4, T3 in plasma. The T4 content negatively depended on amount of energy in diets and milk production in cows at low energy diets. The same trend was found for urea. This study suggests, that the thyroid hormones are essential for arranging energy adaptation. Parallel measurements of T3 and reverse- T3 should be useful tool to confirm existing active and inactive metabolism of T4 in feeding experiments at dairy cattle in future
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