Enhanced Growth and Immune Development in Dwarf Chickens Treated with Mammalian Growth Hormone and Thyroxine

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Abstract
The effects of growth hormone [GH] and/or thyroxine [T4] treatments on antibody production, primary lymphoid organ development and general body growth were examined in 2 dwarf strains (sex-linked dwarf.sbd.SLD, and autosomal dwarf.sbd.ADW) and in a normal-growing strain (K) of White Leghorn chickens. One day-old male chicks were assigned to experimental groups and were treated either with T4 feed supplements or daily mammalian GH injections or a combination of these treatments (T4/GH). Within the SLD strain, GH treatments resulted in a significant enhancement (P < 0.005) of humoral immune responsiveness and bursal growth while T4 treatments significantly (P < 0.05) stimulated thymic growth. Overall growth in the SLD was also stimulated by T4 treatments. GH and/or T4 treatments had no specific effects on primary lymphoid organ growth in the ADW strain but either treatment separately resulted in a significant (P < 0.05) increase in overall body size. None of the treatments signficantly (P > 0.05) affected any of these parameters in the K-strain controls. Supplementation with T4 significantly elevated serum T4 between strains within any of the treatment groups. Serum triiodothyronine (T3) levels were significantly lower in all treatment groups of the SLD compared to the K-strain control. ADW serum T3 levels were significantly lower than the K-strain only in the T4-treated group. No differences (P > 0.05) were found between the dwarf and control strains in endogenous GH levels, although mammalian GH treatments did produce significant changes in serum T3 and T4 levels within the K-strain. Hormonal manipulations can significantly affect body growth, primary lymphoid organ development and immune function in the dwarf strains studied. These strains may be useful models for future studies on hormonal interactions and immune function.