Abstract

A total of 378 Cobb-500 male broilers were used to evaluate the effects of two fiber sources, differing in hydration capacity and fermentability, on gastrointestinal tract development, apparent ileal digestibility and performance from 1 to 42d of age. There were 9 replicates per each of the 3 dietary treatments, all in mash form: a wheat-soybean control (CON) diet, CON diet diluted with 1.5% of wood lignocellulose (LC diet) as a non-fermentable insoluble fiber with high hydration capacity; and CON diluted with 1.5% of a mixture of fibers (ISFC diet) containing both lignified insoluble fiber and a prebiotic soluble fiber fraction from fructooligosaccharides. Additionally, the fermentability of both fiber sources (LC and ISFC) was determined by in vitro using cecal inoculum from broilers fed the experimental diets. Both LC and ISFC treatments impaired by 4% feed conversion ratio only during the first 7d (P = 0.003) compared with CON group. In the grower period (21-42d), the ISFC group showed the best growth (P = 0.039), and at 42d tended to show the highest body weight (P = 0.095). This agrees well with the highest ileal dry matter (P = 0.033) and organic matter (P = 0.043) digestibility observed in ISFC group and the similar trend observed for ileal protein digestibility (P = 0.099) at 42d. Also, at 42 d, absolute and relative (% body weight) digestive tract weights (P ≤ 0.041) and empty gizzard weights (P ≤ 0.034) were greater for LC and ISFC groups compared to CON. The molar proportion of valerate was greatest in ISFC group (P = 0.039). In vitro gas production was higher for ISFC than for LC substrate when using either a diet-adapted or non-adapted cecal inoculum (P < 0.05). These results show the interest in combining IF with prebiotic highly fermentable fiber, such as fructooligosaccharides, in broilers to improve nutrient digestibility and finishing performance.