Experimental design, birds, housing, and diets
The experimental protocol of this study was approved by the Ethical Committee of Animal Experiments of Sylhet Agricultural University, Sylhet, Bangladesh. A total of 1200 unsexed one-day-old Cobb broiler chicks were obtained from a commercial hatchery and used in this experiment. Immediately after thetheir arrival of chicks at the farm, chicks were weighed (41.07 g) and randomly allotted into six dietary groups, each of which included eight replicates of 25 birds per replicate, performed in a completely randomized design.
The chicks were reared in 48 floor pens littered with rice husk (L×W= 90 cm × 255 cm) in an open-sided housing system from day 1 to day 35 age. Environmental conditions inside the chicks rearing pens were not controlled; therefore, they varied withaccording to natural summer conditions outside (April to May, 2018). The average shed temperature was around 28oC28°C with a diurnal variation ranging between 25–34oC25–34°C, and the relative humidity was 79%, with a variation between 55–99%. The light was continuous during the first day, and a 23 h: 1 h lightening: darkness regimen was employed afterward. The birds were immunized against Gumboro and Newcastle diseases, administering BCRDV (against Newcastle) aton the 4th and 19th day and 228E (against Gumboro) aton the 11th day of the birds. Before formulating the experimental diets, homogenous subsamples of raw materials (corn, soybean meal, rice polish, and meat and bone meal) were analyzed for dry matter (DM), crude protein (CP), and crude fiber (CF) contents using by following standard methods (AOAC, 2005). Calcium content was determined by atomic absorption spectrophotometer and P by AOAC (2005). Amino acids analyses were conducted for all feed ingredients before feed formulation by using the HPLC-based method. Diets were formulated to meet or slightly exceed all nutrient recommendations for broilers (Cobb Breeder Recommendation, 2014).