IMPACT OF HEAT STRESS ON GROWTH AND PRODUCTIVITY OF BROILER CHICKENS

Abstract

In this research we introduced chronic cyclic heat stress to assess the productivity, physiological response, oxidative stress, and meat quality of commercial broiler chickens. Over 35 days, two hundred forty-one broilers of the Ross 308 strain were randomly distributed between two treatments: thermoneutral (22±1°C) and cyclic heat stress (33±1°C for 8 hours/day). With continuous heat stress, severe growth impairment was observed (the daily weight gain, feed conversion ratio, and mortality were increased by 33.6%, 7.8%, and 9.3% [1.7% in thermoneutral], respectively), and the final body weight was increased by 30.7% (from 2.845 to 1.973 kg/bird). The metabolic responses were hyperthermia (5.98% increase in rectal temperature), respiratory alkalosis (blood pH 7.29 vs. 7.42), and a 299% increase in plasma corticosterone. Strong oxidative stress, with an increase of 237% in malondialdehyde levels and a decrease of 53% in the total antioxidant capacity, was observed. The intestine showed damage, including a 51% reduction in the villus/crypt height ratio and a 471% increase in the heterophil/lymphocyte (severe immunosuppression) ratio. The meat quality also deteriorated as drip loss increased 151% and shear force increased 64%. There was a strong correlation between the temperature-humidity index and performance depression, which resulted in estimated economic losses of $235/1000 birds. The results show that chronic exposure to heat stress causes multi-systemic disturbances in addition to the feed intake reductions, suggesting the need for multiple (genetic, nutritional, and environmental) approaches to maintain broiler production in the context of climate change.