Effects of Protease, Phytase and a <i>Bacillus sp</i>. Direct-Fed Microbial on Nutrient and Energy Digestibility, Ileal Brush Border Digestive Enzyme Activity and Cecal Short-Chain Fatty Acid Concentration in Broiler Chickens

Two experiments were conducted to determine the effects of protease and phytase (PP) and a Bacillus sp. direct-fed microbial (DFM) on dietary energy and nutrient utilization in broiler chickens. In the first experiment, Ross 308 broiler chicks were fed diets supplemented with PP and DFM in a 2×2 factorial arrangement. The 4 diets (control (CON), CON + PP, CON + DFM, and CON + PP + DFM) were fed from 15–21 days of age. In Experiment 1, significant interaction (P≤0.01) between PP and DFM on the apparent ileal digestibility coefficient for starch, crude protein, and amino acid indicated that both additives increased the digestibility. Both additives increased the nitrogen retention coefficient with a significant interaction (P≤0.01). Although no interaction was observed, significant main effects (P≤0.01) for nitrogen-corrected apparent ME (AMEn) for PP or DFM indicated an additive response. In a follow-up experiment, Ross 308 broiler chicks were fed the same experimental diets from 1–21 days of age. Activities of ileal brush border maltase, sucrase, and L-alanine aminopeptidase were increased (P≤0.01) by PP addition, while a trend (P = 0.07) for increased sucrase activity was observed in chickens fed DFM, in Experiment 2. The proportion of cecal butyrate was increased (P≤0.01) by DFM addition. Increased nutrient utilization and nitrogen retention appear to involve separate but complementary mechanisms for PP and DFM, however AMEn responses appear to have separate and additive mechanisms.本研究开展两项试验，旨在探究蛋白酶（protease）、植酸酶（phytase，以下简称PP）以及芽孢杆菌属（Bacillus sp.）直接饲喂微生物（direct-fed microbial，以下简称DFM）对肉用仔鸡日粮能量与养分利用率的影响。试验一采用2×2完全因子设计，为罗斯308肉用仔鸡饲喂添加PP与DFM的日粮，共设置4种试验日粮：基础对照组（CON）、CON+PP组、CON+DFM组以及CON+PP+DFM联合组，饲喂周期为15~21日龄。试验一结果显示，PP与DFM对淀粉、粗蛋白质及氨基酸的回肠表观消化系数存在极显著交互作用（P≤0.01），且两种添加剂均可显著提升上述养分的消化率；二者均可提升氮沉积系数，且该指标同样存在极显著的交互作用（P≤0.01）。尽管PP与DFM未对氮校正表观代谢能（AMEn）产生交互作用，但二者对该指标均存在极显著的主效应（P≤0.01），呈现加性响应模式。后续试验（试验二）同样采用罗斯308肉用仔鸡，饲喂相同的试验日粮，饲喂周期为1~21日龄。试验二结果表明，添加PP可极显著提升肉用仔鸡回肠刷状缘麦芽糖酶、蔗糖酶及L-丙氨酸氨基肽酶的活性（P≤0.01）；而添加DFM仅使蔗糖酶活性呈现升高趋势（P=0.07）。此外，添加DFM可极显著提升肉用仔鸡盲肠丁酸的占比（P≤0.01）。综合来看，PP与DFM提升养分利用率及氮沉积的作用机制彼此独立但相互补充，而二者对AMEn的调控则呈现独立的加性作用模式。