Effects of a monocomponent protease on performance and protein utilization in 7- to 22-day-old broiler chickens.

A study was conducted with an exogenous monocomponent protease added to corn-soybean meal diets fed to straight-run Ross 708 broilers from 7 to 22 d of age. Broilers were randomly placed into 42 battery pens (5 birds/pen) and allocated to 6 treatments with 7 replicates. A positive control diet (PC; 22.5% CP) and a low protein basal diet (20.5% CP) were formulated. Low protein diets (LP) comprised 98.67% of low protein basal diet and 1.33% Celite (indigestible marker and filler; Celite Corp., Lompoc, CA). Protease [75,000 PROT units/g; 1 PROT unit is defined as the amount of enzyme that releases 1 µmol of p-nitroaniline from 1 µM of substrate (Suc-Ala-Ala-Pro-Phe-p-nitroaniline per minute at pH 9.0 and 37°C] was added at the expense of Celite (0 mg/kg, LP0; 100 mg/kg, LP100; 200 mg/kg, LP200; 400 mg/kg, LP400; and 800 mg/kg, LP800) to create the LP diets (20.25% CP). At 22 d of age, ileal contents were collected from all birds for apparent CP and amino acid (AA) digestibility determinations. Broilers fed the PC diet were 7.5% heavier (P < 0.05) compared with those fed the LP0 diet. Birds fed the LP diets containing protease regardless of concentration grew as well as the birds fed the PC diet. Feed conversion was impaired (P < 0.05) in birds fed the LP0 and the LP100 diets compared with those fed the PC diet, but no difference was found between birds fed the PC diet and those fed diets containing more protease (LP200, LP400, and LP800). Digestibility of CP was increased (P < 0.05) in broilers fed the LP-supplemented diets compared with those fed either the PC or LP0 diets, but it was similar between those fed LP diets with any protease concentration. Digestibility of AA was not different between the PC and LP0 diets. The protease used in this study restored live performance and digestibility of CP (6.1%). When benefits in AA digestibility occurred, they were similar at all protease inclusions and averaged as follows: Arg, 3.5%; Ile, 3.2%; Lys, 5.4%; Thr, 7.8%; Asp, 6.5%; His, 3.3%; Cys, 4.6%; and Ser, 5.5%. Methionine was increased only at 400 and 800 mg/kg (6.5%) and Val was increased only at 200 and 800 mg/kg (5%).