PLASMA TRI-IODOTHYRONINE AND THYROXINE IN YOUNG GROWING CALVES

Publisher Website
Google Scholar
Abstract
Changes in the plasma concentration of T3 [triiodothyronine] and T4 [thyroxine] were compared in male and female calves from birth to 22 wk of age. Calves have increased concentrations of T3 and T4 at birth. T4 and T3 were very high immediately after birth (140 .mu.g/l and 548 .mu.g/l) and fell rapidly to 1/5 of the initial concentrations at 1 wk. A small rise in T3 and T4 at wk 2 and 3 was followed by a gradual decrease in T3 that reached a nadir at about 6 wk of age. For T4, lowest values were at 6 wk in females and 8 wk in males. After 6 wk, T3 gradually increased in both sexes; normal adult values attained at 18 wk of age were about 80% higher than the 6 wk concentration. Body weights of male and female calves were similar during the first 4 wk of life; thereafter, during the 6-22 wk period, male calves grew more rapidly. At the same time plasma T4 concentrations in males were significantly higher than in females. In several groups higher T3 concentrations in males were observed, but differences did not reach significance because of large variability. Although the general pattern of changes in plasma T4 and T3 during the postnatal and early growth period were similar, T4: T3 ratios increased from 271 .+-. 20 (combined values for both sexes .+-. SEM) on the day of birth to 552 .+-. 34 by 6 wk of age, then fell again to 375 .+-. 33 at 22 wk.

This publication has 1 reference indexed in Scilit: