Endocrine changes during the first four hours of extra-uterine life of lambs as related to body weight and rectal temperatures

In order to examine postpartum (pp) changes of concentrations of thyroid stimulating hormone (TSH), thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3), growth hormone (GH) and cortisol (C) in newborn lambs, blood samples were taken at birth, 1, 2, and 4 h pp. Plasma TSH and T4 remained unchanged during this early postnatal period. A significant increase of T3 was observed at 1 h pp, while a continuous decrease in rT3 and GH was found during the 4-period. C decreased sharply at 1 h pp and remained stable from 1 to 4 h pp. Rectal temperatures (rt) were increased significantly (P<0.005) at 1 h pp and did not change during the following 3 h. In a second part of the experiment, blood sampling was performed once only at birth in order to determine correlations between the different hormones, rt and body weight (BW), respectively, in twins and triplets. Absence of strong correlations between thyroid hormones, BW and rt, and results of factor analyses indicate that thyroid hormone levels at birth are not related to rt or BW and hence not to survival chances of lambs, either twins or triplets.