The main purpose of this study was to investigate the effect of different levels of fiber and fat on perform-ance, pH, and viscosity of digesta in young broilers. A total of 420 one-day-old male chicks Ross 308 were assigned to 60 cages of seven birds each. The birds fed with 15 experimental diets produced by central composite design (CCD), containing three levels of sugar beet pulp (SBP: 0.00, 1.75, 3.50%), tallow (T: 0.00, 0.50, 1.00%) and soybean oil (SO: 0.00, 0.50, 1.00%) from 0 to 14 d. The results showed that maxi-mum average daily body weight gain (ADG: 42.10 g/b/d) and minimum feed conversion ratio (FCR: 0.99) were observed with diet containing 0.35% SBP, 0.00% T and 0.51% SO. Maximum (4.64) and minimum (3.01) pH in gizzard were found with diets containing 0.00% SBP, 0.51% T, 0.27% SO and 1.70% SBP, 0.21% T and 0.00% SO, respectively. The highest (6.94) and lowest (5.86) pH in ileum contents were ob-tained with diets comprising 0.00% SBP, 1.00% T, 0.43% SO and 1.47% SBP, 0.00% T, and 0.00% SO, respectively. Maximum (3.54) and minimum (1.50) viscosity in ileal digesta were observed with diets con-taining 3.50% SBP, 1.00% T, and 1.00% SO and 0.00% SBP, 0.00% T and 0.53% SO, respectively. This experiment has revealed that, the CCD and response surface methodology (RSM) have the efficiency to describe the relationships between different levels of SBP, T and SO and the ability to predict the optimal point of the level of diet ingredients in order to achieve the best performance. With increasing the amount of SBP and decreasing the level of T and SO in the diets, the pH of digesta in the gizzard and ileum de-creased. The ileum digesta viscosity increased with increasing SBP, T, and SO levels.

Keywords