PERORAL ADMINISTRATION OF TRIIODOTHYRONINE (T-3) AFFECTS ABSORPTION OF IMMUNOLACTOGLOBULINS IN CALVES

On the basis of our studies which demonstrated that T-3 is a natural m ilk-borne component of cow mammary secretions, this study investigated the influence of T-3 (and thyroxine, T-4) on the serum lg level (used here as an indicator of intestinal absorption). Forty healthy carves were given a single dose of either T-3 or T-4 with the first colostrum meal 6 h following birth. Blood samples were taken before and 42-50 h after hormone administration. The T-4 treatment resulted in metabolic changes that were reflected by an increase in blood glucose, triglyce rides (TG), non-esterified fatty acids (NEFA), and a decrease in total serum proteins (TP). Ig levels were reduced from 27.5 g/l (controls) to 20.6 g/l. The T-3 treatment caused an increase in serum TG and FFA (p < 0.01), and, in contrast to T-4, an increase in TP and Ig (p < 0.0 01). These results indicated that peroral administration of T-3, but n ot T-4, could exert a positive effect on the transfer of immunolactogl obulins in the neonatal calf intestine. The contrasting hormonal effec ts are likely attributable to different responses of intestinal cells to T-3 and T-4.