The response of broilers to insoluble fibre and exogenous enzymes in low protein diets

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The Australian poultry industry is focused on developing a successful low crude protein (CP) feeding program for broilers. Reduced CP broiler diets have the potential to provide a number of benefits, including enhanced environmental outcomes, increased bird welfare and reduced input costs. However, as dietary CP is reduced, growth performance is often impaired, body fat and fat pad weights are increased, and gut health is negatively affected. These effects are more prominent in broilers fed a wheat-based diet compared to a maize-based diet, and this brings a further challenge to the Australian industry as broiler diets in Australia are based on wheat.

The decreased performance of broilers associated with feeding a low CP diet cannot be fully recovered by supplementation of essential amino acids (AA). To restore the performance loss in broilers associated with feeding a low CP diet, the use of specific non-essential AA, whole grains and enzymes has been explored, but with limited success. The addition of sugarcane bagasse and other fibre sources to the diet has been demonstrated to improve performance due to their action on gastrointestinal functionality, such as improved gizzard development, increased digestibility of nutrients and modulation of digestive enzyme production and nutrient transporters in the digestive system. However, whether this improves the performance of broilers fed a reduced protein diet remains unclear.

This project investigated the effects of insoluble fibre and/or protease as a nutritional strategy to improve growth performance and gut health of broilers offered low CP diets supplemented with crystalline AA. The key finding was that a 20 g/kg or less reduction of dietary CP in a wheat, sorghum and soybean meal-based diet negatively affected growth performance of broilers. This was characterised by lower feed intake, lower weight gain, higher feed conversion ratio (FCR) and higher abdominal fat pad, even if low CP diets were supplemented with crystalline AA.

Thus, performance loss in broilers fed low CP diets may not be fully recovered by supplementation of essential AA and glycine. Sugarcane bagasse at 20 g/kg in both normal and low CP diets decreased FCR and increased weight gain and relative gizzard weight of birds. The performance loss in broilers associated with 20 g/kg reduction in dietary CP can be fully restored for FCR and partly restored for body weight by including bagasse in the diets.

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