Effects of crude protease produced by Bacillus subtilis (MAFIC Y7) on growth performance, immune indices, and anti-inflammatory responses of broilers fed soybean meal- or cottonseed meal-based diets.

A strain of Bacillus subtilis (MAFIC Y7) was isolated from the intestine of Tibetan Pigs and was able to express high protease activity. The aim of this study was to characterize the proteases produced by MAFIC Y7 and to investigate the effects of proteases addition on growth performance, ileal amino acid digestibility, and serum immunoglobulin and immune factors of broilers fed SBM- based diets, or on growth performance, carcass characteristics, and intestinal morphology of broilers fed CSM-based diets. Bacillus subtilis (MAFIC Y7) expressed protease showed its optimal enzyme activity at 50°C and pH 7.0. Coated crude enzyme (CCE) showed greater stability at pH 3.0 than its uncoated counterpart. Experiment 1 was conducted with six diets based on three levels of crude protein (CPlow, CPmedium and CPhigh) with or without CCE. In CPlow, CCE increased G:F ( d 1 - 21, d 1 - 42) by 8%, 3% respectively, and enhanced apparent ileal digestibility (AID) of crude protein and lysine (on d 42 ) by 8.8%, 4.6% respectively, compared with diets containing no CCE (P < 0.05). Coated crude enzyme increased G:F during d 1 - 21 from 0.63 to 0.68, improved G:F and average daily gain (ADG) during d 1 - 42, and enhanced apparent ileal digestibility of crude protein, lysine, cysteine, and isoleucine on d 42 compared with the unsupplemented treatments (in CPmedium, P < 0.05). Coated crude enzyme increased serum IgA (on d 21), serum IgA and IgG and increased serum IL-10 (on d 42), but decreased serum TNF-α (on d 21), and serum IL-8 and TNF-α (on d 42) compared with unsupplemented treatments. At CPhigh, CCE decreased serum levels of IL-6 and TNF-α (on d 21), and IL-8 and TNF-α (on d 42) compared with unsupplemented treatments (in CPhigh, P < 0.05). In Experiment 2, CSM- based diets with two lysine to protein ratios (5.2% or 5.5%) with or without CCE". In the high Lys diet (5.5% Lys:protein), CCE increased ADG and G:F, increased carcass, but decreased abdominal fat compared with the unsupplemented treatment (P < 0.05). In the 5.2% Lys:protein dietary treatment, CCE improved duodenal villus height compared with the unsupplemented treatment (P < 0.05). Supplementation of protease produced by MAFIC Y7 was associated with lower inflammatory responses in SBM diets (CPmedium or CPhigh) and improved ADG in broilers feed CPmedium or CPhigh. The proteases improved ADG and efficiency of CSM use when the ratio of Lys to protein was 5.5%.