Peroral administration of triiodothyronine (T3) affects absorption of immunolactoglobulins in calves.

On the basis of our studies which demonstrated that T3 is a natural milk-borne component of cow mammary secretions, this study investigated the influence of T3 (and thyroxine, T4) on the serum Ig level (used here as an indicator of intestinal absorption). Forty healthy calves were given a single dose of either T3 or T4 with the first colostrum meal 6 h following birth. Blood samples were taken before and 42-50 h after hormone administration. The T4 treatment resulted in metabolic changes that were reflected by an increase in blood glucose, triglycerides (TG), non-esterified fatty acids (NEFA), and a decrease in total serum proteins (TP). Ig levels were reduced from 27.5 milligrams (controls) to 20.6 milligrams. The T3 treatment caused an increase in serum TG and FFA (p < 0.01), and, in contrast to T4, an increase in TP and Ig (p < 0.001). These results indicated that peroral administration of T3, but not T4, could exert a positive effect on the transfer of immunolactoglobulins in the neonatal calf intestine. The contrasting hormonal effects are likely attributable to different responses of intestinal cells to T3 and T4.