Total serum thyroxine concentration during ontogenic development of sheep
Reklewska, B.
Acta Physiologica Polonica 26(2): 139-147
1975
ISSN/ISBN: 0044-6033 PMID: 1146559 Document Number: 86641
There were 2 series of observations, in consecutive years, on crossbred lambs, ewes and adults of both sexes. Total thyroxine (T4) was estimated in serum by a competitive protein-binding radioassay and the measurements were related to body size as W0.75. In the first experiment the measurements began at 0 to 3 h after birth, before suckling, when the mean value of T4 was high, roughly 12 mu g/100 ml. About 1 h after suckling a rise of almost 2 mu g occurred and thereafter there was a fall to 7.5 mu g on the 3rd day and a further decline to about 4 mu g at 8 months and 3 mu g at 18 months. In the second experiment the course was similar with a fall from 10.4 mu g in male lambs and 11.6 in females during the first day to minimum values of 1.9 and 2.7 at 120 days and 4.4 and 4.0 at 360 days. There was a strong correlation between T4 (y) and W0.75 at weights from 2 to 14 kg, but not a higher weights: y = -28.73/W0.75 + 1.95 (r = 0.846). In early life, to 6 months of age, T4 was higher in female than in male lambs; later there was no significant difference.