Response of Broilers to Dietary Inclusions of Different Insoluble Fibre Sources in a Reduced Crude Protein Diet

Recent studies have shown that the decreased performance of broilers associated with feeding a reduced crude protein (RCP) diet cannot be fully recovered by supplementing essential amino acids (Hilliar et al., 2019). We hypothesized that the dietary inclusion of moderate amounts of insoluble fibre would improve gizzard function and protein/amino acid digestibility that could help to restore the performance loss associated with feeding a RCP diet. This study investigated the effects of oat hulls, soy hulls, sugarcane bagasse or lignocellulose based product as insoluble fibre sources in a RCP diet fed to broilers.

A total of 672 d-old Ross 308 male parental birds were fed a common starter diet until 10 d of age. On d 10, birds were assigned into 6 treatments with 8 replicates of 14 birds per pen. The treatments were: a normal protein diet (NP, grower 211 g/kg CP, finisher 195 g/kg CP), a RCP diet (CP reduced by 20 g/kg in grower and finisher phases) and RP diets formulated with either sugarcane bagasse at 20 g/kg, lignocellulose based product at 10 g/kg, oat hulls at 30 g/kg, or soy hulls at 30 g/kg. The basal diet of fibre treatments was the same and the formulations were adjusted by adding Celite, an indigestible component as a filler. The basal diet contained wheat, sorghum and soybean meal as major ingredients and was supplemented with xylanase and phytase. The diets met Ross 308 nutrient specifications with digestible lysine levels of 11.5 g/kg and 10.2 g/kg in grower (10 to 24 d) and finisher (24-35 d) phases, respectively. Feed intake, weight gain, and FCR were determined from d 10 to 35. Carcass parameters were measured on d 35. Data were subjected to one way analysis of variance using SPSS v. 22 and significance was determined at P < 0.05 using Duncan’s multiple range test.

During d 0 to 35, dietary treatments had a significant effect on feed intake (P < 0.001), weight gain (P < 0.001), FCR (P < 0.01), as well as relative weights of abdominal fat pad (P = 0.0501), and gizzard (P < 0.001). The birds fed the RP diet with soy hulls or bagasse had a lower FCR compared to those fed RP diet without fibre and similar FCR to those fed NP diet (RP- 1.460, RP + bagasse- 1.443, RP + soy hulls- 1.448, and NP- 1.439). The birds fed RP diet with soy hulls had higher body weight gain compared to those fed RP diet without fibre and similar body weight gains to RP + bagasse and NP treatments (RP- 2190 g, RP + bagasse- 2227 g, RP + soy hulls- 2263 g, and NP- 2298 g). Adding insoluble fibre sources to the RP diet had no effect on relative fat pad weight. The birds that received the RP diet with oat hulls or bagasse had higher relative gizzard weight compared to those that received RP and NP diets (NP- 11.49, RP- 11.47, RP + oat hulls13.24, and RP + bagasse- 12.56 g/kg).

These findings suggest that performance loss in broilers associated with 20 g/kg CP reduction in a wheat, sorghum and soybean meal based diet can be fully restored for FCR and partly restored for body weight by including either 20 g/kg sugarcane bagasse or 30 g/kg soy hulls in the diets. Further research is warranted to examine the dose response of selected fibres and the effect of particle size distribution of fibres on performance of broilers offered reduced crude protein diets.

ACKNOWLEDGEMENTS: This research was funded by the AgriFutures Australia.