The effects of dietary soluble and insoluble fibers on broiler chickens performance and gastrointestinal tract histomorphology

The influence of dietary soluble and insoluble fibers on small intestine histomorphology and performance was studied in broilers from 1 to 21 d of age. The treatments were as follows: treatment 1, control diet (fiber-free diet); and treatments 2, 3, 4, and 5 where 2% and 4% cellulose (CEL), 2% and 4% carboxymethyl cellulose (CMC) were respectively supplemented to the control diet, respectively. Inclusion of CMC reduced body weight gain (BWG), average feed intake (AFI), and production efficiency factor (PEF) and increased feed conversion ratio (FCR) as compared with others (P<0.05). Inclusion of 4% fiber (CEL and CMC) led to increase gizzard weight at 10 d of age (P<0.05), but at d 21, both 2% and 4% levels of this fibers resulted in the mentioned effect. The weight of the gizzard was increased when high level of fibers (4%) was included in the diet (P<0.05). Higher weights of small intestine were observed in birds fed CEL and CMC than those of fed control diet at 21 d of age (P<0.05). Orthogonal comparisons showed, in comparison with control and CEL, CMC increases relative weights of digestive organs except for duodenum (P<0.05). Based on the orthogonal comparisons, inclusion of fibers decreased the pH of gizzard contents at 10 and 21 d of age (P<0.05), while this effect for CMC was observed only at 21 d of age. Inclusion of CMC led to an increase in jejunal viscosity rather than other treatments (P<0.05). The CMC-fed birds had lower villous height and width, deeper crypt, lower villous length to crypt depth ratio, lower villous surface area compared with others (P<0.05). The effects of different treatments on goblet cells type were not significan (P>0.05).  However, the CMC-fed birds had the thicker serosa and have the greater goblet cell numbers as compared to others (P<0.05). Current findings suggest that the effects of fiber on broiler performance and digestive tract histomorphology differ depending on the fiber type.