The Role of Photoperiod and Melatonin on Alleviation of the Negative Impact of Heat Stress on Broilers

Abstract

Two experiments were conducted to test that broilers, reared under intermittent light program or fed a diet containing melatonin, would dampen the deleterious effects of heat stress on their performance and immune response. In the first experiment, two groups of one-day-old male broiler chicks received 23h Light: 1h Dark (CL), while another two groups received intermittent light (IL) (1hL: 3hD) programs. From 4-6 weeks of age, a group from each lighting program was exposed to heat stress (35 °C). The other two groups were kept under 24 °C. At 35 °C, birds under IL program had 5 times less mortality and 41% higher body weight at six weeks of age compared to the CL birds. Moreover, heat-stressed birds under IL program had 11% better feed conversion and higher T₃ concentrations and antibody production, compared to the CL group. In the second experiment, two groups of one-day-old male broiler chicks were fed a diet containing 40 ppm melatonin (MEL) while another two groups received a MEL-free diet, from 4-6 weeks of age. Concurrently, a group from each MEL treatment was reared under 35 °C. The other two groups were kept under 24 °C. Under 35 °C, birds receiving MEL had less mortality, better feed conversion and higher antibody production, compared to the MEL-free diet group. There were no significant differences in body weight, feed consumption and T₃ concentrations between these two groups. These results indicate that IL program may be used effectively to improve broiler's ability to alleviate the negative effects of heat stress more than MEL administration does.