Effect of thiouracil-induced hypothyroidism on the humoral immunity of New Hampshire chickens.

Two experiments were conducted to examine the effects of feeding a diet containing .1% thiouracil to two lines of New Hampshire chickens differing in growth rate and relative bursa size. Body weight, serum 3,5,3'-triiodothyronine, and thyroxine were reduced by the thiouracil treatment. The primary total anti-sheep red blood cell (SRBC) titer in Experiment 1 was higher for thiouracil-fed (TF) chicks at 7 days postprimary immunization (PPI). In Experiment 2, the total anti-SRBC titers were higher for control chicks 3 days PPI; but from 5 to 10 days PPI, TF chicks had higher titers. During the secondary response in both experiments, the total anti-SRBC titers were not consistently higher for one dietary group over the other from 3 to 10 days postimmunization. Mercaptoethanol-resistant antibody titers were not significantly different between the two dietary groups in either experiment during the primary and secondary responses. Thiouracil-fed chicks had higher immunoglobulin G (IgG) and M (IgM) concentrations in serum during both the primary and secondary responses in Experiment 2. Although there was no genotype effect on antibody production to SRBC, serum immunoglobulins were different between lines. Small bursa line (SBL) chickens had higher serum IgG while the IgM concentrations of chicks from the Lester J. Dreesen strain were greater than those of SBL.