PSII-18 Effects of temperature-humidity index, age and breed on egg-laying rate in four Korean Native chicken breeds.

Abstract This study analyzed the effects of the Temperature-Humidity Index (THI), age and breed on the egg-laying rate in four native Korean chicken breeds. Data from 3,738 birds were collected from 2022 to 2024 at Gyeongsang National University Farm, including Korean Rhode Island Red, Korean White Leghorn, Korean Brown Cornish, and Hwanggalsaek-Jaeraejong chickens. Egg-laying rates were measured from 18 to 65 weeks of age, combined with meteorological data from the Jinju area to evaluate external conditions. Regression and repeated measurement analysis were conducted using SAS 9.4. The THI was calculated using the formula: THI = (1.8 × T + 32)-[(0.55-0.0055 × RH) × (1.8 × T - 26.8)], where RH is the average relative humidity (%), and T is the average temperature (°C). THI analysis showed the highest egg-laying rate in the 40-49 range (35.84±20.57%) and the lowest in the 80-89 range (25.93±20.61%). Age analysis revealed higher egg-laying rates at 30-39 weeks (37.07±19.66%) and above 40 weeks (37.86±19.62%). By breed, Korean Rhode Island Red showed the highest egg-laying rate (54.13±12.23%), while Korean Brown Cornish had the lowest (10.24±9.58%). GLM analysis indicated that high humidity (p< 0.01) and daily temperature range (p< 0.01) significantly affected egg-laying rates, with maximum temperature (p=0.01) and minimum temperature (p< 0.01) also being important factors. Interaction analyses between THI, age and breed showed that all factors and their interactions had significant effects (p< 0.01). This study suggests that maintaining THI in the 45-49 range is crucial for optimizing egg-laying rates in Korean native chickens and emphasizes the need for breed-specific environmental management. These results provide scientific evidence for efficient management and productivity improvement in Korean native chicken production, contributing to sustainable livestock industry development.