The effect of NSP-degrading enzymes on gut physiology and growth performance of turkeys fed soybean meal and peas-based diets

Highlights

• Peas is an effective dietary protein and energy supplement for turkeys.

• High dietary levels of peas don’t affect diet, dietary fiber, or fat digestibility.

• NSP-degrading enzymes increase butyrate production and improve performance.

• The incidence of Foot Pad Dermatitis is lower when NSP-degrading enzymes are used.

Abstract

The aim of this study was to determine nutrient digestibility, short chain fatty acids (SCFA) production, bacterial enzyme activities and production performance effects of peas as an alternative dietary protein source. Diets containing peas were fed to growing turkeys for 8 weeks. The experimental design involved two diets, a wheat-soybean meal (SBM) diet and a wheat-SBM-peas diet, each with and without the addition of NSP-degrading enzymes. Peas were added at 300 g/kg at the expense of wheat and SBM. Nutrient digestibility, energy metabolizability and nitrogen retention remained unchanged in all groups. The SBM and peas diets did not affect the final body weights (BW) of birds, but the peas diet significantly (P < 0.05) increased FCR relative to the SBM diet (1.80 vs. 1.74 kg/kg). Enzyme supplementation significantly increased the final BW of turkeys (3.88 vs. 3.75 kg), irrespective of the diet type. A diet by enzyme interaction revealed that during the first 4 weeks of feeding, the enzyme preparation improved feed utilization in the SBM diet but not in the peas diet (1.37 vs. 1.44 kg feed/kg BWG). Enzyme supplementation decreased apparent ileal viscosity (1.60 vs. 1.82 mPas). Cecal ammonia concentrations and the activity of bacterial β-glucosidase, β-xylosidase, and α-arabinofuranosidase decreased significantly in response to peas diets, irrespective of enzyme supplementation. Enzyme supplementation significantly decreased β-glucosidase activity and the SCFA pool in the ceca, regardless of diet type. A diet by enzyme interaction revealed that the NSP-degrading enzyme supplements significantly decreased cecal SCFA concentrations but only in the peas diet (163 vs. 221 μmol/g). Excreta moisture content was significantly lower in the peas diet, regardless of enzyme supplementation and diet type. The Foot Pad Dermatitis (PFD) score was considerably (P < 0.05) reduced in the peas diet (1.43 vs. 1.53–1.60 in the remaining groups). In conclusion, peas could be effectively used in the diets of young growing turkeys at 300 g/kg at the expense of wheat and SBM without any negative effects on the gastrointestinal function and final BW. However, higher FCR values were noted for the peas diet. The benefits of the NSP-degrading enzymes included a decrease in ileal viscosity and excreta moisture content, an increase in cecal butyrate production, and an increase in the final BW of turkeys.

Introduction

Carbohydrates, including readily digestible starch (Svihus, 2013) and low-digestible non-starch polysaccharides (NSP) (Smeets et al., 2018), are the main components of poultry diets, accounting for 60–70 % of the ration. Cereals, including wheat, are the major source of starch in poultry diets, whereas NSP are present in both cereals and soybean meal (SBM). Non-starch polysaccharide content is higher in SBM than in wheat (210 vs. 113 g/kg) (Bao and Choct, 2010). In cereal grains, non-cellulosic polysaccharides consist mainly of arabinoxylans and β-glucans whereas arabinans, arabinogalactans, galactans, galactomannans, mannans, and pectic polysaccharides predominate in SBM and peas. The latter fraction has been considered to include diverse types of polysaccharide structures based on linked units of rhamnose, galacturonic acid, galactose, and arabinose (i.e., rhamnogalacturonans, galacturonans, arabinans) (Beg et al., 2001; Chesson (2001); Slominski, 2016).

Due to the low digestibility of oligosaccharides and NSP in the gastrointestinal tract (GIT) of poultry (Nalle et al., 2010), the apparent metabolizable energy content of SBM is approximately 28 % lower in poultry than in swine (National Research Council (NRC, 1994). The presence of NSP decreases dietary energy concentrations and exerts antinutritional effects by restricting the access of digestive enzymes to nutrients and slowing down the intestinal transit time (Bach Knudsen, 2014). Structural NSP act by encapsulating nutrients, including protein and starch (Khadem et al., 2016). As well, the soluble fraction of NSP binds water thus increasing excreta viscosity (Hetland et al., 2004). Ultimately, NSP inclusion decreases nutrient digestibility (Cozannet et al., 2017) and apparent metabolizable energy (AME) content of the diet, thus increasing the feed conversion ratio (FCR) (Bedford and Schulze, 1998; Hetland et al., 2004).

Two main strategies can be considered to minimize the antinutritional effects of NSP, namely the selection of cereals with lower amounts of water-soluble NSP (Shewry and Lovegrove, 2014), and dietary supplementation with exogenous enzymes capable of digesting polysaccharide complexes and releasing starch and protein trapped inside the endosperm (Bedford and Schulze, 1998). Depolymerization of NSP requires enzymes specific to the main and side chain structures of NSP (Bhat, 2000; Cowieson and Adeola, 2011; Slominski, 2016). In chickens fed wheat/SBM-based diets, a commercial xylanase product increased starch digestibility and AME levels (Choct et al., 1999). Earlier research has indicated that mostly xylanase and β-glucanase have been used for degrading NSP in wheat- and barley-based poultry diets (Choct, 2006). A new approach involves the use of enzyme “cocktails” (multi-carbohydrases) and is aimed at decomposing a broader spectrum of NSP (Meng and Slominski, 2005; Meng et al., 2005; Cozannet et al., 2017; Mikulski et al., 2017).

In experiments with chickens (Hughes et al., 2004; Abdulla et al., 2016), the addition of exogenous enzymes to diets improved energy utilization. One of the few experiments with turkeys revealed that the dietary supplementation with exogenous enzymes my help alleviate the adverse effects of NSP on nutrient utilization (Ayoola et al., 2015). In another study, the efficacy of exogenous phytase increased slightly in cornstarch-SBM-based diets supplemented with xylanase, and no such effects were observed in wheat-SBM-based diets (Ingelmann et al., 2018). The influence of NSP-degrading enzymes on GIT development and function in young turkeys fed diets containing various cereals and high-protein ingredients remains to be explored.

The objective of this study was to evaluate the physiological response of the upper and lower GIT of young turkeys (up to 8 weeks of age) to diets containing 30 % of peas and a blend of NSP-degrading enzymes. It was hypothesized that the 300 g/kg inclusion of peas would not affect nutrient digestibility, GIT function, or the growth performance of turkeys when compared with a standard wheat-SBM-based diet.