Genetic perspectives on thermal tolerance in native chickens using non-linear growth models and temperature-humidity indices

The aim of this study was to determine the best non-linear model, between the Gompertz and sinusoidal models, for estimating the absolute growth rate (AGR) of Pradu Hang Dum chickens and examine the appropriate temperature-humidity index (THI) equation for studying heat stress in these chickens. The growth of Pradu Hang Dum chickens was monitored from hatching to 16 weeks of age. Males consistently had higher body weights than females, with the difference becoming more pronounced over time. AGR was estimated using both models, with the sinusoidal model providing a marginally better fit than the Gompertz model (adjusted R-square of 0.9991, Durbin-Watson statistic of 3.248, MSE of 446.68108, and AIC of 54589.104). Climate data revealed an average air temperature of 27.0 °C and relative humidity of 72.1 %. Regression analysis indicated that the THI2 equation developed by Tao and Xin (2003) provided the best fit for examining heat stress. The relationship between AGR and THI, based on both phenotypic and genetic analyses, indicated that the effects of heat stress on growth performance began to emerge at a THI value of approximately 27. Genetic parameters, including heritability, decreased with increasing THI levels, suggesting that higher temperatures negatively affect the genetic potential for growth. These findings underscore the importance of using the AGR as a dynamic measure of growth performance and highlight the need for effective management strategies to mitigate the effects of heat stress on poultry production. Further research is needed to explore these relationships and develop sustainable solutions to enhance the growth and productivity of Pradu Hang Dum chickens under various environmental conditions.