Systematic review and meta-analysis of the effect of feed enzymes on growth and nutrient digestibility in grow-finisher pigs: Effect of enzyme type and cereal source

Dietary supplementation of pig diets with exogenous enzymes has been suggested as a strategy to increase nutrient digestibility and improve feed efficiency in grow-finisher pigs. However, inconsistent results are found in the literature. Ingredient composition of the diets is one of the most important sources of variation that may affect enzyme efficacy and consistency of results. A systematic review and a meta-analysis was therefore conducted to determine which exogenous enzymes with which diet type most consistently improve pig growth, nutrient digestibility and feed efficiency. Enzyme type and dietary cereal source were the main explanatory variables included in the models. The mean difference effects of enzyme supplementation on average daily gain (ADG), average daily feed intake (ADFI), gain to feed (G:F), apparent ileal digestibility (AiD) and apparent total tract digestibility (ATTD) of dry matter (DM), crude protein (CP), and gross energy (GE) were calculated for each study and these were used as the effect size estimates in the meta-analysis. A dataset with 139 comparisons from 67 peer-reviewed publications was used in the meta-analysis. In response to enzyme supplementation, G:F was improved in 38 of the 120 comparisons reporting pig growth data, remained un-changed in 78 and deteriorated in 4. Overall, DM and GE AiD, and ATTD were improved by xylanase, xylanase + β-glucanase, mannanase and protease dietary supplementation (P < 0.05). Crude protein AiD was only improved by protease dietary supplementation (P < 0.001). Dietary supplementation with xylanase alone improved ADG of maize- (P < 0.05) and co-product- (P < 0.05) based diets but had no effect on the G:F of grow-finisher pigs. Dietary supplementation with xylanase + β-glucanase had no effect on ADG, ADFI and G:F. Protease supplementation tended to improve the ADG of grow-finisher pigs fed co-product-based diets (P = 0.08) but had no effect on G:F. Dietary supplementation with multi-enzyme complexes improved the ADG (P < 0.05) and G:F (P < 0.01) of maize-, wheat-, barley- and co-product-based diets. In conclusion, dietary supplementation with all enzyme types improved nutrient digestibility depending on ingredient content, while mannanase and multi-enzyme complex supplementation most consistently improved growth and feed efficiency.