Effect of different exogenous proteases on growth performance, nutrient digestibility, and carcass response in broiler chickens fed poultry by-product meal-based diets

This study was conducted to examine the effect of different proteases with varied optimum pH range (acid and neutral) on growth performance, nutrient digestibility, and carcass characteristics of broiler chickens fed poultry by-product meal-based diets. The acid protease contained 50,000U/g and the neutral protease contained 25,000U/g of premix. The broiler chickens (n=200) were assigned to 5 treatments with 4 replicate pens per treatment and 10 broiler chickens per pen in a completely randomized design. Five diets were iso-energetic and iso-nitrogenous (metabolizable energy, 2850kcal/kg; crude protein, 20%) and broiler chickens had ad libitum access to diets for 35 d. A corn-soybean meal-based negative control (NC) diet was formulated on digestible amino acid basis. A positive control (PC) corn-soybean meal-based diet containing 3% poultry by-product meal was formulated on digestible amino acid basis, and it was supplemented with acid protease mix (80g/t; PC-A), neutral protease mix (160g/t; PC-N), or 50/50 combination of the two (120g/t; PC-C). Overall feed intake was not affected by any of the treatment. However, broiler chickens fed the PC-C diet had improved (P<0.05) body weight gain compared with the NC diet during d 0–35. Except the PC diet, broiler chickens had improved (P<0.05) feed conversion ratio (FCR) compared with those fed the NC diet during the starter phase (d 0–21). The broiler chickens fed the PC-N and the PC-C diets improved FCR compared to the NC diet during d 0–35. The broiler chickens fed all the diets, except the NC diet, improved (P<0.05) apparent total tract digestibility for nitrogen (ATTDn), while broiler chicken fed the PC-C diet improved (P<0.01) N retention (Nret) compared with other diets. Improved (P<0.01) apparent metabolizable energy (AME) and AME corrected for N (AMEn) was noted in broiler chickens fed the PC-A, and the PC-C diets compared with other diets. However, carcass characteristics, e.g., carcass yield, breast meat yield, thigh weight, abdominal fat pad, and relative liver and heart weights, were not affected by treatments. In conclusion, broiler chickens fed the PC-C diet had better growth performance, energy and nutrient digestibility compared to the NC diet.