Effects of exogenous enzymes and direct-fed microbial on broiler performance and nutrient digestibility when fed variable inclusions of soy products

The objective was to examine the effects of feed additive combinations, including xylanase, amylase, and protease enzyme (XAP), with β-mannanase (MAN) or direct-fed microbial (DFM) supplementation on broiler performance and nitrogen corrected apparent metabolizable energy (AMEn) when fed diets containing various soy products concentrations. Two experiments were conducted from 10 to 21 d of age by feeding three soy product inclusions of low (20%), intermediate (28%), and high (35%). Feed additive combinations were supplemented across the three concentrations of dietary soy in both experiments. In experiment 1 there was no enzyme supplemented, XAP (100 g/MT) alone, and XAP with MAN (100 g/MT or 50 g/MT). In experiment 2 there was no supplementation, XAP (100 g/MT) alone, and XAP with DFM (100 g/MT or 50 g/MT). Experiment 1 resulted in reduced feed intake (P ≤ 0.01) and increased body weight gain (BWG) (P ≤ 0.10) with intermediate and high soy compared to low soy inclusion. Supplementation with all enzyme combinations decreased feed intake (P ≤ 0.01) compared to non-supplemented diets and improved feed efficiency (FE; P = 0.02) and feed conversion ratio (FCR; P = 0.01). There was an interaction between soy inclusion and enzyme supplementation as XAP+½MAN improved AMEn (P = 0.05) in high soy treatments. In experiment 2, there was an interaction as the intermediate soy diet with XAP and DFM decreased BWG (P = 0.02) compared to all other soy combinations, no treatment differed from control diets without enzyme. Feed intake was not different, and high soy improved FE and FCR compared to low and intermediate soy (P ≤ 0.05). Enzyme supplementation with XAP alone improved FE and FCR over the combination of XAP and DFM (P ≤ 0.05). Low soy decreased AMEn (P ≤ 0.01) compared to intermediate and high soy. Overall, high soy diets out-performed low soy treatments possibly due to increased fiber in low soy diets from DDGS and canola meal ingredients. In experiment 1, FE and FCR were improved with all combinations of enzyme and AMEn of high soy diets was increased with enzyme supplementation demonstrating a positive effect of enzyme addition. In experiment 2, XAP and DFM did not improve broiler performance, possibly due to a well-established microbial population in the gastrointestinal tract by the time feed additive supplementation occurred