The reaction of the thyroid gland to the thyrotropic hormone “load” in high and low-yielding cows

The studies were carried out on cows of Holstein black-and-white breed. 2 groups 10 heads each formed. milk yield for lactation was thousand kg in the first group, and - 5 second group. Blood collected from subcaudal vein monthly during lactation. T 3 4 determined blood serum. functional “load” thyroid gland performed at peak (3 months) its end 9 months. TSH preparation a dose 0.5 u/kg live weight administered intramuscularly an empty stomach before morning feeding. hormones injection one two hours after injection. Kath calculated using formula Т 1 – 0 / where is coefficient activity hormones. levels During lactation, level production varies inversely with average daily yield. period high productivity (2,3,4 months lactation), concentration both low, later increased maximum 8th month reserves high-yielding are lower relation to low-yielding cows.