Abstract
This study was conducted to evaluate the effects of temperature-humidity index (THI) on the mortality and the panting rates in hens exposed to varying thermal environments. Hens were challenged with an acute elevation in THI in Experiment 1, where dry-bulb temperature and relative humidity were set at ~27°C and 56% at the beginning of the experiment and changed to 36°C and 45% at its conclusion, respectively. In Experiment 2, different groups of hens were exposed to a progressive increase in THI, with similar ranges to those used in the previous experiment. In Experiment 3, the hens used in Experiment 2 were again challenged by THI conditions, the intensity of which ranged between those used in the previous two experiments. In Experiment 4, panting rates were recorded under varying THI. In the last, plasma biochemical profiles were determined in blood taken from hens subjected to experimental conditions similar to those in Experiment 2. When THI was acutely elevated from 24.2° to 32.1°C within 1 h and then maintained over 4.5 h, no mortality was detected in the first hour, but exceeded 95% after 5 h, and reached 100% at 5.5 h. A gradual increase in THI to 31.2°C over 6 h did not result in mortality during the first 3 h. When THI was set below the conditions in Experiment 1 but above those in Experiment 2, mortality was 29% at 4 h, 75% at 5 h, and 79% at 8 h. However, no mortality was detected in their respective control groups. Panting was not observed under 25.3°C and was largely variable under 30°C. However, all hens exhibited panting exceeding 250 counts/min and 60% mortality at 34°C when heat stress continued for a duration of up to 280 min. In Experiment 5, high ambient THI resulted in significant reductions in plasma albumin, amylase and aspartate aminotransferase, compared with those in control group (P < 0.05). These results suggest that an acute elevation of THI has more severe effects on mortality in hens than gradual changes even when temperature and humidity are similar in both cases.
Highlights
The effects of heat stress in poultry include reduced feed intake, body weight gain, and production performance along with increased mortality [1,2,3,4], which results in a loss of profits in poultry farms
Mortality was not detected during the first hour of heat stress, but there was more than 95% mortality in hens at 5 h, and 100% mortality at 5.5 h
No mortality was detected in the hens from the treatment group in Experiment 2 that were exposed to an ambient environment with temperature-humidity index (THI) of 31.2◦C which was achieved over 6 h after the initiation of heat stress (THI was 24.3◦C at 0 h) and maintained for the 3 h (Figure 2A)
Summary
The effects of heat stress in poultry include reduced feed intake, body weight gain, and production performance along with increased mortality [1,2,3,4], which results in a loss of profits in poultry farms. These negative effects are accompanied by deterioration in meat quality [5], animal welfare [2, 6,7,8], and immune functions [3]. Poultry are vulnerable to high temperature environments since they are covered with feathers and do not have sweat glands These two factors reduce the efficiency of heat exchange between the body and the environment that is normally observed in animals with sweat glands. Increasing their rate of respiration is one of the key ways by which birds maintain their body temperature under increasing environmental temperatures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
