Dietary Fiber Level Improve Growth Performance, Nutrient Digestibility, Immune and Intestinal Morphology of Broilers from Day 22 to 42

Dietary fiber is considered to be a nutrient concentration diluent and an antinutritional factor affecting poultry performance. As a consequence, commercial diets generally contain 2-3% crude fiber. However, crude fiber is also a functional component of normal digestive organ function. Moderate dietary fiber could promote the development of digestive organs, increase digestive enzyme activity and nutrient digestibility, improve health status and enhance growth performance in poultry. At present, there are few systematic studies on the dietary fiber requirements of broilers in the late feeding stage. Therefore, it is of great practical significance to determine the dietary fiber requirements of broilers. Under the conditions of this experiment, a diet with 7-9% crude fiber may promote growth performance by improving the nutrient digestibility, immunity and intestinal morphology of broilers from day 22 to 42. There are few systematic studies on the dietary fiber requirements of broilers in the late feeding stage, and there are not enough data to support this hypothesis. This experiment was conducted to examine the effects of dietary fiber level on growth performance, nutrient digestibility, immune function and intestinal morphology of broilers from day 22 to 42. A total of 480 one-day-old Arbor Acres broilers with half male and half female were randomly allocated into four groups, with eight replicates in each group and fifteen chickens in each replicate. The experimental period was 42 days. All broilers were fed a basal diet from 1 to 21 days. During the 22-42 day period, the four experimental groups were fed diets with soybean hulls as the fiber source, and crude fiber (CF) levels were 2%, 5%, 8% and 11%, respectively. The results showed that during the 29-42 day period, the average daily feed intake (ADFI) of broilers was higher in the 5% CF and 8% CF groups (p < 0.05), and during the 29-35 day period, the average daily gain (ADG) of broilers was higher and the ratio of feed and gain (F/G) of broilers was lower in the 5% CF and 8% CF groups (p < 0.05). The digestibility of crude protein (CP), ether extract (EE), CF, acid detergent fiber (ADF) and neutral detergent fiber (NDF) was higher in broilers of the 8% CF group (p < 0.05). The immunoglobulin A (IgA), immunoglobulin G (IgG) and immunoglobulin M (IgM) content of the plasma of broilers was higher in the 8% CF group (p < 0.05). The villus height (VH) of the duodenum, jejunum and ileum of broilers was higher, and the crypt depth (CD) was lower in the 8% CF group than that in the 2% CF group (p < 0.05). The ratio of VH and CD (V/C) of the duodenum and jejunum of broilers in the 8% CF group was higher than that in the 2% CF group (p < 0.05). The quadratic regression analysis showed that the optimum dietary CF level was 7-9%. In conclusion, under the conditions of this experiment, a diet of 7-9% CF may promote growth performance by improving the nutrient digestibility, immunity and intestinal morphology of broilers from day 22 to 42.