Dietary treatments were a maize-soya bean meal based diet as control, and diets containing 0.25, 0.50, 0.75, or 1.00% of POP. Diets (Table 1) were formulated to meet nutritional requirements of broiler chickens according to Ross 308 nutritional recommendation. All diets were provided in mash form and feed and water were provided ad libitum. The conditions and standards of broiler chickens rearing used in this experiment were approved by the Ethics Committee for Animal Experiments (University of Kurdistan, Sanandaj, Iran). A total of 280 one-day old (Ross 308) male broiler chickens obtained from a local hatchery and were randomly allocated into 20 floor pens
(100 150 cm2 ) arranged in a well-ventilated windowless house. Each treatment consisted of four replicate pens with 14 broiler
chickens. Pens floor covered with fine wood shavings as litter material
and equipped with a bell-type drinker and a tube feeder.
Environmental temperature was set at 32 °C for the first week and
29 °C for the second week, which was further decreased to 21 °C
until the end of the experiment. In the first two days of the experiments
and the light programme was 23 h of light per day.