Effects of type and particle size of dietary fiber on growth performance and digestive traits of broilers from 1 to 21 days of age

A trial was conducted to study the effects of type and particle size of dietary fiber on growth performance and digestive traits of broilers from 1 to 21 d of age. There was a negative control diet with 1.54% crude fiber, a positive control diet that included 3% cellulose (CEL), and 4 additional diets arranged factorially that included 3% oat hulls (OH) or sugar beet pulp (SBP) ground through a 0.5- or a 2.0-mm screen. For the entire experimental period, fiber inclusion improved BW gain (P <= 0.01) and feed conversion ratio (P <= 0.001), but particle size of the fiber source did not affect performance. The relative weight of the gizzard was higher (P <= 0.001) with OH and SBP than with CEL or the control diet. Also, gizzard weight decreased (P <= 0.001) with a reduction in particle size of the fiber source. Fiber inclusion increased HCl concentration and reduced gizzard pH (P <= 0.01), and the effects were more noticeable with OH and SBP than with CEL. Fiber inclusion increased total tract apparent retention of nitrogen (P = 0.001) and soluble ash (P <= 0.001) as well as the AME(n) of the diet (P <= 0.001). All of these effects were in general more pronounced with OH than with CEL, with SBP being intermediate. A reduction in particle size of the OH and SBP improved total tract apparent retention of DM (P <= 0.001), nitrogen (P <= 0.05), and soluble ash (P <= 0.01) as well as the AME(n) of the diet (P <= 0.05). It is concluded that additional OH and SBP improves gizzard weight and growth performance in young chicks fed low-fiber diets and that the effects are more pronounced with OH than with CEL. Particle size of OH and SBP does not affect broiler performance, but coarse grinding increases gizzard development and reduces nutrient digestibility in young birds.