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Genetics of heat tolerance and thyroid function in Athens-Canadian randombred chickens
1Department of Poultry Science, University of Georgia, 30602, Athens, GA, USA.
Summary
Genetic variation in chickens influences thyroid hormones (T3, T4), body weight, and heat stress survival. While T4 and T3 levels are heritable, selecting for these traits may not improve heat tolerance without impacting body weight.
Area of Science:
- Animal Genetics
- Avian Physiology
- Thermoregulation
Background:
- Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), play crucial roles in avian metabolism and thermoregulation.
- Understanding the genetic basis of thyroid function and its relationship with heat tolerance is vital for poultry breeding.
- Heat stress poses a significant challenge to poultry production, impacting animal welfare and economic outcomes.
Purpose of the Study:
- To investigate the genetic variation in thyroid hormone levels (T3, T4), body weight, and heat stress survival time in chickens.
- To determine the heritability of these traits and their phenotypic and genetic correlations.
- To assess the potential of using these traits as selection parameters for improving heat tolerance in poultry.
Main Methods:
- Five experiments involving bovine thyroid stimulating hormone (TSH) injections to measure T3 and T4 levels.
- Assessment of heat stress survival time by exposing chickens to high temperatures (50 °C).
- Calculation of heritability and phenotypic/genetic correlations for body weight, T3, T4, and heat stress survival.
Main Results:
- Thyroxine (T4) levels increased significantly after TSH stimulation, with high heritability observed.
- Both T4 and T3 levels after TSH injection were moderately heritable, while T3 alone showed low heritability.
- Heat stress survival time did not differ between groups with innate high or low T4 levels.
- Significant negative correlations were found between heat stress survival time and body weight/T4, and positive correlations between T4 and T3.
- Genetic correlation analysis indicated that selecting for T4 or T3 alone may not enhance heat tolerance without negatively affecting body weight.
Conclusions:
- Thyroid hormone levels (T4, T3) and body weight exhibit significant genetic variation in chickens.
- While T4 and T3 are heritable, they are not ideal sole selection criteria for improving heat tolerance due to potential negative impacts on body weight.
- Further research is needed to identify robust genetic markers for heat tolerance in poultry that consider multiple physiological and growth parameters.
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