A systematic review and meta-analysis of the growth performance effects of feeding diets containing corn distillers dried grains with solubles (cDDGS) and feed enzymes to broiler chickens

Numerous studies have been conducted to determine the effects of feeding diets containing variable inclusion rates of corn distillers dried grains with solubles (cDDGS), with and without supplemental enzymes, on growth performance of broilers but responses among these studies are inconsistent. Therefore, a systematic review and a meta-analysis of results from studies published from 2009 to 2018 was conducted to: 1) quantitatively summarize the impact of feeding cDDGS diets on body weight gain (BWG), feed intake (FI), and gain to feed ratio (G:F); and 2) evaluate the effect of adding various types of exogenous enzymes (xylanase; complex = multi-carbohydrases; cocktail = multi-carbohydrases plus protease) without or with phytase on growth performance of broilers. Mean differences of BWG, FI, and G:F were expressed as a per-centage between feeding control corn-soybean meal (SBM)-based diets and diets containing cDDGS to broilers using data from 20 studies with 71 observations. Likewise, mean differences were determined for the same growth performance variables reported in 10 studies that provided 47 observations comparing the effects of adding exogenous enzymes to corn-SBM-based diets and cDDGS diets. The heterogeneity (I2-statistic, %) across studies was calculated based on Cochran's Q-statistic method, and was 66.7% for BWG, 63.4% for FI, and 33.1% for G:F, indicating low similarity (homogeneity) between studies. Mixed multi-variable models were applied to address the factors affecting high heterogeneity which included dietary energy system, oil content of cDDGS, and feeding period. Adding cDDGS to broiler diets resulted in a 1.0% decrease (P < 0.01) in G:F for the overall feeding period. Feeding cDDGS to finisher broilers resulted in a 0.78% improvement (P < 0.05) for BWG and 1.60% improvement (P < 0.01) for FI. However, starter broilers (1-21 days of age) fed cDDGS diets had 2.44% lower (P < 0.05) BWG and 3.18% less (P < 0.01) FI compared with feeding corn-SBM diets. Broilers fed diets containing less than 100 g/ kg cDDGS had the greatest improvement (P < 0.01) in BWG (4.52%), followed by a 2.32%