RESUMO
Increasing of oxygen consumption in fast growing broiler chickens is associated with the more pronounced occurrence of right ventricular hypertrophy and ascites. While, rearing of susceptible chickens in dark condition could reduce the metabolic rate of birds and hence the incidence of ascites. The present study was designed to investigate a comparative study on the influence of different dark-length schedules on the incidence of ascites and metabolic parameters in fast growing broiler chickens. A total of 1000 day-old [Pure Sir Broiler Line Arian] chickens were obtained and subjected to four different lighting programs. Dead birds were autopsied for the lesions of ascites. Weekly growth performance of chickens was determined and blood samples were taken, on days 7, 12, 21, 28, 35 and 42 of age for hormonal analysis. The incidence of ascites was clearly higher in birds subjected to normal lighting program compared with those of dark exposed chickens. Control chickens showed significantly higher body weight compared to the dark exposure group birds at day 21 of age, while it did not differ at days 28, 35 and 42 of age. Such differences was accompanied with the lower levels of plasma T3 and T4 concentrations in dark group chickens than to control chickens at the earlier age [days 12 and 21]. This phenomenon indicated a reduction of metabolic rate and oxygen consumption in dark group chickens that had been led to reducing of ascites incidence. Our data proves that increasing dark-length instead of continuous lighting may be beneficial for rearing of broiler chickens, especially, when the risk of ascites incidence is higher