Supplementation of specific insoluble fibres partially attenuates compromised growth performance of broilers fed wheat-based reduced crude protein diets

Insoluble fibre has been shown to be a functional fibre that helps the effective use of nutrients and energy through the gastrointestinal tract, and as such may be added to diets to enhance the growth performance of broilers. This study aimed to investigate the effects of insoluble fibre sources in a reduced protein (RP) diet fed to broilers. At d 10 post-hatch, 672 d-old Ross 308 male birds were assigned to 6 treatments with 8 replicates of 14 birds each. The treatments were a normal protein (NP) diet, a RP diet (-20 g/kg protein), and RP diets formulated with either sugarcane bagasse at 20 g/kg, lignocellulose-based fibre at 10 g/kg, oat hulls at 30 g/kg, or soy hulls at 30 g/kg. The results showed that the reduction in dietary protein decreased feed intake and weight gain, and worsened feed conversion ratio (FCR; <i>P</i> < 0.05). The birds fed the RP diet with soy hulls or bagasse had a better FCR (<i>P</i> < 0.05) compared to those fed the RP diet without fibre and similar FCR to those fed a NP diet. Bagasse or soy hulls supplementation in the RP diet decreased (<i>P</i> < 0.05) the starch digestibility coefficient compared to the RP diet without fibre. Lower counts (<i>P</i> < 0.05) of <i>Lactobacillus</i> in birds offered the RP diet with bagasse or oat hulls was observed compared to the RP diet alone. The difference (<i>P</i> = 0.011) in the expression of digestive enzyme genes in response to dietary treatments was observed for the <i>AMY2A</i> gene in the pancreas. The reduction in dietary crude protein (CP) downregulated (<i>P</i> < 0.05) the <i>AMY2A</i> gene and the addition of the four insoluble fibres to the RP diet had no effect on the expression of <i>AMY2A</i> compared to the RP treatment but bagasse, lignocellulose, and soy hulls added RP diets had similar <i>AMY2A</i> expression as the NP treatment. It was concluded that reducing dietary protein compromised the growth performance of broilers which was partially attenuated by supplementing the diets with bagasse or soy hulls.