Abstract
Corn is a common energy source in pig diets globally; when financially warranted, industrial corn coproducts, such as corn distiller’s dried grains with solubles (DDGS), are also employed. The energy provided by corn stems largely from starch, with some contribution from protein, fat, and non-starch polysaccharides (NSP). When corn DDGS are used in the diet, it will reduce starch within the diet; increase dietary protein, fat, and NSP levels; and alter the source profile of dietary energy. Arabinoxylans (AXs) comprise the majority of NSP in corn and its coproducts. One strategy to mitigate the antinutritive effects of NSP and improve its contribution to energy is by including carbohydrases within the diet. Xylanase is a carbohydrase that targets the β-1,4-glycosidic bonds of AX, releasing a mixture of smaller polysaccharides, oligosaccharides, and pentoses that could potentially be used by the pig. Xylanase is consistently effective in poultry production and moderately consistent in wheat-based swine diets, but its efficacy in corn-based swine diets is quite variable. Xylanase has been shown to improve the digestibility of various components of swine-based diets, but this seldom translates into an improvement in growth performance. Indeed, a review of xylanase literature conducted herein suggests that xylanase improves the digestibility of dietary fiber at least 50% of the time in pigs fed corn-based diets, but only 33% and 26% of the time was there an increase in average daily gain or feed efficiency, respectively. Intriguingly, there has been an abundance of reports proposing xylanase alters intestinal barrier integrity, inflammatory responses, oxidative status, and other health markers in the pig. Notably, xylanase has shown to reduce mortality in both high and low health commercial herds. These inconsistencies in performance metrics, and unexpected health benefits, warrant a greater understanding of the in vivo mechanism(s) of action (MOA) of xylanase. While the MOA of xylanase has been postulated considerably in the literature and widely studied in in vitro settings, in wheat-based diets, and in poultry, there is a dearth of understanding of the in vivo MOA in pigs fed corn-based diets. The purpose of this review is to explore the role of xylanase in corn-based swine diets, discuss responses observed when supplemented in diets containing corn-based fiber, suggest potential MOA of xylanase, and identify critical research gaps.
Highlights
The purpose of this review is to explore the role of xylanase in corn-based swine diets, discuss responses observed when supplemented in diets containing corn-based fiber, suggest potential mechanism(s) of action (MOA) of xylanase, and identify critical research gaps
For every 15% increase in reduced-oil-corn dried grains with solubles (DDGS) included at the expense of corn, dietary acid-hydrolyzed ether extract increased by nearly 17%, neutral detergent fiber (NDF) increased by 34.2%, CP increased by 27%, starch decreased by 20% (Figure 1A), and estimated net energy (NE) decreased by 83 kcal/kg or 3.5% (Figure 1B)
With increasing levels of reducedoil DDGS, the contribution of fat, fiber, and protein to NE will increase, and the contribution of simple carbohydrates will decrease (Figure 1C). When these components are regressed in relationship to increasing levels of reduced-oil DDGS, for every 1% of corn replaced by reduced-oil corn DDGS, the amount of NE coming from fat, CP, and fiber increases by 0.1%, 0.3%, 0.02%, respectively, but the amount of NE coming from simple carbohydrates decreases by 0.44%
Summary
In 2019, more than one billion metric tonne of corn was produced globally with the United States responsible for more than 30% of that supply. The improvements in the digestibility of unexpected dietary components, such as starch, CP, and various minerals and amino acids, with xylanase supplementation support this MOA These digestibility responses are inconsistent in pigs fed corn-based diets (Kerr et al, 2013; Passos et al, 2015), and digestibility metrics provide no discernment if it is due to the enzyme or modulation of the microbiome. The nutritional and economic value of xylanase is amplified if the caging effect of NSP can be consistently mitigated in vivo; further research is needed to confirm this MOA in corn-based diets Where this mitigation occurs is of importance, as released starch is of more value if released in the small intestine, and amino acids released in the hindgut serve little value to pig. There is a paucity of studies investigating gastrointestinal microbiota composition and phenotypic responses in pigs fed corn-based diets
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