Thyroid activity of selected, nonselected, and dwarf broiler lines

Area of Science:

• Animal Science
• Endocrinology
• Poultry Genetics

Background:

• Growth rates and thyroid hormones are critical for poultry production.
• Athens-Canadian (AC) randombred chickens represent a nonselected line, while commercial broiler lines are selected for rapid growth.
• Sex-linked dwarfism is a trait that can impact growth and metabolism.

Purpose of the Study:

• To compare growth rates and serum thyroid hormone concentrations (T3 and T4) between selected and nonselected chicken lines.
• To investigate the thyroid hormone profiles of a sex-linked dwarf chicken line in relation to growth.

Main Methods:

• Two trials were conducted comparing Athens-Canadian (AC) randombred (nonselected) chickens with commercial broiler (selected) lines.
• A sex-linked dwarf line was included in the second trial.
• Growth rates were measured from 1 through 8 weeks of age.
• Serum concentrations of 3,5,3 -triiodothyronine (T3) and thyroxine (T4) were analyzed.

Main Results:

• Selected line birds exhibited significantly heavier body weights than nonselected line birds from 1 to 8 weeks of age.
• Nonselected line birds were heavier than dwarf line birds during the same period.
• Selected lines had lower serum T3 concentrations compared to nonselected lines, with no significant difference in T4.
• The dwarf line displayed lower T3 and higher T4 concentrations than both selected and nonselected lines.

Conclusions:

• Selection for rapid growth in broiler chickens is associated with altered thyroid hormone profiles, specifically lower T3 levels.
• The sex-linked dwarf line demonstrates a distinct thyroid hormone phenotype, characterized by lower T3 and higher T4.
• The observed thyroid hormone differences in the dwarf line suggest a potentially reduced rate of thyroxine (T4) deiodination to T3.