Productive performance, digestibility, carcass traits and meat quality in rabbits fed triticale-based diets supplemented with xylanase

Cereals such as triticale may contain high levels of xylans and arabinoxylans, limiting its use in diets since they act as anti-nutritional factors. The objective was to evaluate the effects of the enzyme xylanase included in triticale-based diets on productive performance, digestibility, carcass traits and meat quality in growing-finishing rabbits. Eighty rabbits (New Zealand X California breed), 35 days old, with an average initial live weight of 821 ± 26 g, were used. Twenty animals for treatment were used in each one of the fourth experimental treatments: 0, 4000, 8000 and 12,000 XU/kg of xylanase inclusion (XilaBlend 6X). The rabbits were fed ad libitum and fecal excretion was collected on days 7, 14, 21, 28 and 35 of the experimental period. At the end of the experimental period, the rabbits were slaughtered and carcass characteristics and meat quality were measured. A higher (P < 0.05) live weight was observed in rabbits fed diets with the addition of xylanase enzyme on days 4 and 7 of the experimental period. On the other hand, in the average total tract digestibility of organic matter, no significant difference was observed, similar to what occurred in the carcass traits and nutritional quality of the meat. The inclusion of 8000 XU/kg of xylanase enzyme provided the best values of apparent digestibility of total tract protein and dry matter on the finished stage of rabbits.

Multi-copy expression of a protease-resistant xylanase with high xylan degradation ability and its application in broilers fed wheat-based diets

The acidic thermostable xylanase (AT-xynA) has great potential in the feed industry, but its low activity is not conductive to large-scale production, and its application in poultry diets still needs to be further evaluated. In Experiment1, AT-xynA activity increased 3.10 times by constructing multi-copy strains, and the highest activity reached 10,018.29 ± 91.18 U/mL. AT-xynA showed protease resistance, high specificity for xylan substrates, xylobiose and xylotriose were the main hydrolysates. In Experiment2, 192 broilers were assigned into 3 treatments including a wheat-based diet, and the diets supplemented with AT-xynA during the entire period (XY-42) or exclusively during the early stage (XY-21). AT-xynA improved growth performance, while the performance of XY-21 and XY-42 was identical. To further clarify the mechanism underlying the particular effectiveness of AT-xynA during the early stage, 128 broilers were allotted into 2 treatments including a wheat-based diet and the diet supplemented with AT-xynA for 42 d in Experiment3. AT-xynA improved intestinal digestive function and microbiota composition, the benefits were stronger in younger broilers than older ones. Overall, the activity of AT-xynA exhibiting protease resistance and high xylan degradation ability increased by constructing multi-copy strains, and AT-xynA was particularly effective in improving broiler performance during the early stage.

Effects of adaptation diet and exogenous enzymes on true metabolizable energy and cecal microbial ecology, short-chain fatty acid profile, and enzyme activity in roosters fed barley and rye diets

Three experiments evaluated effects of adaptation diet and exogenous β-glucanase and xylanase on TME_n of barley and rye. Single Comb White Leghorn roosters were fed adaptation diets based on corn/soybean meal (SBM), barley/SBM with and without β-glucanase, or rye/corn/SBM with and without xylanase for 4 wk. In Experiments 1 and 2, after the adaptation period, TME_n was determined using a 48 h precision-fed rooster assay for 100% barley or 100% rye diets with or without β-glucanase or xylanase, respectively. Experiment 3 consisted only of feeding adaptation diets for 4 wk. Cecal samples were collected at the end of experiments for microbial ecology, short-chain fatty acid (SCFA) profiles, and enzyme activity analyses. In Experiments 1 and 2, β-glucanase increased (P < 0.05) TME_n of barley, and there was no significant effect of adaptation diet on TME_n values. Total cecal Eubacteria and Ruminococcaceae were decreased (P < 0.05) and Escherichia coli were increased (P < 0.05) at the end of the TME_n assay compared with the end of the adaptation period (with no TME_n assay). There was a large decrease (P < 0.05) for most cecal SCFA at the end of the TME_n assay compared with the end of the adaptation period. Both cecal β-glucanase and xylanase activity were increased for birds fed adaptation diets containing the respective enzyme. In Experiment 3, there were no consistent effects of adaptation diet on cecal microbial profiles or SCFA but cecal β-glucanase activity was increased (P < 0.05) by exogenous β-glucanase for barley and cecal xylanase activity was increased (P < 0.05) by exogenous xylanase for rye. Overall, the results indicated that TME_n of barley was increased by exogenous β-glucanase, adaptation diet did not significantly influence the TME_n response to the dietary enzymes, and cecal fermentation (based on cecal SCFA) was greatly reduced by the TME_n assay. Cecal β-glucanase and xylanase activity, however, were often increased by feeding high barley and high rye diets containing exogenous enzymes.

Exploring competitive inhibition of a family 10 xylanase derived from Hu sheep rumen microbiota by Oryza sativa xylanase inhibitor protein: In vitro and in silico perspectives

The catalytic domain of family GH10 xylanase, XYN-LXY_CD derived from Hu sheep rumen microbiota was expressed in Pichia pastoris X33. The special activity of reXYN-LXY_CD in the culture supernatant was 232.56 U/mg. The optima of reXYN-LXY_CD were 53 °C and pH 7.0. Recombinant Oryza sativa xylanase inhibitor protein (rePOsXIP) competitively inhibited reXYN-LXY_CD with an inhibition constant (K_i) value of 237.37 nM. The concentration of hydrolysates released from beechwood xylan by reXYN-LXY_CD reduced when rePOsXIP was added into the hydrolytic system. Fluorescence of reXYN-LXY_CD was statically quenched by rePOsXIP in a dose-dependent manner. The details in intermolecular interaction between XYN-LXY_CD and OsXIP were investigated by using molecular dynamics (MD) simulations, binding free energy computation and non-covalent interactions (NCI) analysis. Hydrogen bonding and van der Waals played indispensable roles in the XYN-LXY_CD/OsXIP interaction. The α-7 helix of OsXIP tightly occupied the catalytic pocket of XYN-LXY_CD with hydrogen bonding such as K239_OsXIP-N261/Q292/E197_{XYN-LXY_CD} (E197, the acid-base catalytic residue), D236_OsXIP-K327_{XYN-LXY_CD} and Q242_OsXIP-E211/Q212_{XYN-LXY_CD}. Based on the quantum theory of atoms in molecules (QTAIM), the Laplacian of electron density and core-valence bifurcation index of HZ3_K239-OE2_E197 were 0.1025 a.u. and 0.002218, respectively. Elucidating the mechanism underlying xylanase-inhibitor interactions might help construct XYN-LXY_CD mutants that gain resistance to XIPs and high catalytic activity, which would be more efficient in feed additives in livestock.

Experimental and in silico studies of competitive inhibition of family GH10 Aspergillus fumigatus xylanase A by Oryza sativa xylanase inhibitor protein

The family GH10 Aspergillus fumigatus xylanase A (AfXylA10) gene, afxyla10 was cloned and recombinantly expressed in Pichia pastoris X33. The optimum temperature and pH of reAfXylA10 was 53 °C and 7.0, and Mn²⁺ remarkably activated the catalytic activity. The recombinant Oryza sativa xylanase inhibitor protein, rePOsXIP significantly inhibited reAfXylA10 with inhibition constant (K_i) of 177.94 nM via competitive inhibition and decreased the concentration of hydrolysate from beechwood xylan. Optimal inhibition of rePOsXIP on reAfXylA10 occurred at 45 °C for 40 min. The fluorescence of reAfXylA10 was statically quenched by rePOsXIP, indicating the formation of reAfXylA10-rePOsXIP complex during their interaction. Furthermore, molecular dynamics (MD) simulations were performed to obtain the detailed information on enzyme-inhibitor interaction. The binding free energy (ΔG) of AfXylA10-OsXIP complex was -30 ± 9 kcal/mol by MM-PBSA calculation, and the α-7 helix of OsXIP anchored in the catalytic cleft of AfXylA10 by competition with the xylan substrate. K239_OsXIP stably interacted with the catalytic site E140_AfXylA10 through hydrogen bond and vdW interaction. Intermolecular hydrogen bonds T104_AfXylA10/V99_AfXylA10-Q5_OsXIP, R256_AfXylA10-E235_OsXIP, D155_AfXylA10-Y243_OsXIP and D145_AfXylA10-R194_OsXIP on the upper of the TIM barrel were essential for strengthening the stability of complex. Therefore, these non-covalent interactions (NCI) played key role in the interaction between AfXylA10 and OsXIP.

Xylanase impact beyond performance: A microbiome approach in laying hens

Anti-nutritional compounds such as non-starch polysaccharides (NSP) are present in viscous cereals used in feed for poultry. Therefore, exogenous carbohydrases are commonly added to monogastric feed to degrade these NSP. Our hypothesis is that xylanase not only improves laying hen performance and digestibility, but also induces a significant shift in microbial composition within the intestinal tract and thereby might exert a prebiotic effect. In this context, a better understanding on whether and how the chicken gut microbial population can be modulated by xylanase is required. To do so, the effects of dietary supplementation of xylanase on performance, apparent total tract digestibility (ATTD) and cecal microbiome in laying hens were evaluated in the present study. A total of 96 HiSex laying hens were used in this experiment (3 diets and 16 replicates of 2 hens). Xylanase was added to the diets at concentrations of 0, 45,000 (15 g/t Xygest^TM HT) and 90,000 U/kg (30 g/t Xygest HT). The diets were based on wheat (~55%), soybean and sunflower meal. The lowest dosage, 45,000 U/kg, significantly increased average egg weight and improved feed efficiency compared to the control treatment (P<0.05). Egg quality parameters were significantly improved in the experiment in response to the xylanase addition. For example, during the last 28 days of the trial, birds receiving the 45,000 U/kg and the 90,000 U/kg treatments exhibited an increase in Haugh units and albumin heights (P<0.05). Compared with the control, the ATTD of organic matter and crude protein were drastically improved in the 45,000 U/kg treatment group (P<0.05). Furthermore, gross energy and the ATTD of crude fat were improved significantly for birds fed 90,000 U/kg group compared to the control. Importantly, 16S rRNA gene analysis revealed that xylanase at 45,000 U/kg dosage can exert a change in the cecal microbiome. A significant increase in beneficial bacteria (Bacilli class; Enterococcaceae and Lactobacillales orders; Merdibacter, Enterococcus and Nocardiopsis genera; Enterococcus casseliflavus species) was documented when adding 45,000 U/kg xylanase to the diet of laying hens. In conclusion, dietary supplementation of xylanase 45,000 U/kg significantly improved laying hen performance and digestibility. Furthermore, microbiome data suggest that xylanase modulates the laying hen bacterial population beneficially, thus potentially exerting a prebiotic effect.

Comparing the efficacy of stimbiotic and a combination of xylanase and beta-glucanase, in broilers fed wheat-barley based diets with high or low AME

A stimbiotic is defined as a product that stimulates a fiber-degrading microbiome to increase fiber fermentability. The aim of this study was to examine if it is more advantageous to feed a stimbiotic (xylanase + xylo-oligosaccharides [STB]) or a combination of xylanase and beta-glucanase (Xyl + BG) to broilers fed wheat-barley based diets with differing AME levels. Cobb 500 broilers (n = 480, 80 birds per treatment) were fed 6 dietary treatments in a 2 × 3 factorial arrangement; 2 AME levels, ‘High’ or ‘Low’, which differed by 100 kcal ME/kg, and 3 additive supplementations, with no supplemental additives, STB or Xyl + BG. Diets were fed as 3 phases, starter (d 0–14), grower (d 14–21) and finisher (d 21–35). On bird age d 14, 21 and 35, total pen body weight and feed intake were determined, and feed conversion ratio corrected for mortality (cFCR) was calculated. On d 21 and d 35 ileal viscosity and beta-glucan content and caecal SCFA concentration were determined. Additive suplementation had no impact on cFCR in birds fed the low AME diet, but in birds fed the high AME diet the cFCR value was reduced in the presence of the additives (P = 0.001 and P = 0.015, at d 14–21 and d 21–35, respectively). At d 21, cecal SCFA concentration was consistently higher (P = 0.015), and ileal beta-glucan level lower (P = 0.002), in birds fed the diet supplemented with STB compared to those without additives. At d 35, ileal viscosity was lower in birds fed STB compared to those fed the diet without supplementation of additives, irrespective of diet AME level (P = 0.017). These results suggest that both STB and Xyl + BG ameliorate the antinutritive effects of the non-starch polysaccharides (NSP) present in wheat-barley based diets, resulting in improved bird performance. However, supplementation with STB induces a comparatively greater positive effect on NSP hydrolysis and SCFA production.

Engineering of thermostable phytase-xylanase for hydrolysis of complex biopolymers

Industrial processing of enzymes requires higher heating that affects the thermal stability of the enzyme and increases the production cost. In this study, xylanase-phytase (XP) fusion protein was generated via co-expression in a single vector with a cold-shock promoter, leading to improved activity at optimal pH, temperature and the thermal behaviour of the protein. Xylanase-phytase (XP) fusion and phytase proteins were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The XP fusion was thermally stable up to 124 °C, higher than phytase which was steady up to 113.5 °C. XP fusion exhibits higher stability at its thermal transition midpoint (T _m) 108 °C, higher than the T _m value of phytase which is 90 °C. Industrially efficient and environment-friendly proteins with low production cost and higher stability can be generated by 'fusion protein' technology.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02936-z.

The effects of exogenous xylanase supplementation on the in vivo generation of xylooligosaccharides and monosaccharides in broilers fed a wheat-based diet

1. This study quantified xylanase-induced changes in soluble monosaccharides, xylooligosaccharides (XOS) and volatile fatty acid (VFA) contents of the different sections of the gastrointestinal tract (GIT) and whether these were related to altered bird performance. 2. An in vitro digestion of the wheat-based diet was carried out with the xylanase (Econase XT at 16,000BXU/kg diet) to compare the in vitro and in vivo generation of these XOS and monosaccharides. For the in vivo study, 80 male Ross 508 b roiler chicks were split into two groups fed a wheat-based diet with or without Econase XT (16,000BXU/kg diet) for 21 days. 3. There were no effects of Econase XT inclusion on growth performance characteristics, likely a result of the high-quality wheat diet, the corresponding high performance of the control group (FCR average of 1.45 in controls) and the relatively young age of the birds (from four to 26 days of age). 4. Econase XT supplementation increased the xylotetraose (X₄) content in the colon (P = 0.046, enzyme x GIT section interaction) and the xylose contents in the colon and caeca (P < 0.001, enzyme x GIT section interaction). 5. The trend for increased acetate production in the caeca of Econase XT treated birds (P = 0.062) suggested that the XOS generated were subsequently fermented in the caeca, potentially impacting upon the types of microbiota present. 6. The present study suggested that wheat arabinoxylan degradation was enhanced by xylanase supplementation, which may have increased the production of beneficial volatile fatty acids (VFA) in the caeca, and thereby potentially modulated the caecal microbiome, but without affecting bird performance at this early age.

Influence of meat and bone meal, phytase, and antibiotics on broiler chickens challenged with subclinical necrotic enteritis: 2. intestinal permeability, organ weights, hematology, intestinal morphology, and jejunal gene expression

Undigested proteins entering the hindgut may favor the proliferation of Clostridium perfringens. Using phytase to eliminate the need for meat and bone meal (MBM) as a P source may reduce potential infection with C. perfringens. A study was conducted to determine the impact of MBM, phytase, and antibiotics (AB) on intestinal permeability and morphology, organ weights, and jejunal gene expression in Ross 308 chickens challenged with subclinical necrotic enteritis (NE). Male Ross 308-day-old chicks (672 each) were randomly allocated to 8 treatments with 6 replicate pens each housing 14 birds. A 2 × 2 × 2 factorial arrangement of treatments was used: MBM (no or yes); AB (no or yes-Zn bacitracin 100 in S and 50 ppm in G/F and salinomycin Na 60 ppm in all phases); phytase (500 or 1,500 FTU/kg, both using 500 FTU matrix values) using wheat-SBM-canola meal diets. Birds were challenged with Eimeria spp on day 9, and C. perfringens strain EHE-NE18 on day 14 and 15. An AB × MBM interaction (P < 0.05) was detected for relative gizzard weight (with contents) being lower in birds fed MBM and AB compared to those fed MBM and no AB. A MBM × AB interaction (P > 0.01) was detected for lymphocyte counts being lower with MBM and AB compared to MBM without AB. A phytase × AB interaction (P < 0.05) was observed for villi length being increased with high phytase and no AB compared to with AB. Inclusion of MBM increased (P < 0.05) blood FICT-d concentration, whereas AB decreased it (P < 0.05). Antibiotics increased RBC (P < 0.05), Hgb (P < 0.05), and PCV (P < 0.05) and expression of Ca-binding protein, CALB1 (P > 0.05). Inclusion of MBM decreased expression of MUC2 (P < 0.05). Results indicate that dietary MBM has a detrimental effect on gut health of broilers but this may be counteracted using AB.

A novel Bacillus based multi-strain probiotic improves growth performance and intestinal properties of Clostridium perfringens challenged broilers

There is a necessity for the implementation of in-feed probiotics in the poultry production industry, following strict regulations around the use of antibiotic growth promoters (AGP). Bacillus spp. are becoming an attractive alternative because of their functionality and stability. This study aims to evaluate the effect of a novel multi-strain Bacillus based probiotic on growth performance and gut health in male Ross 308 broiler chickens challenged with Clostridium perfringens Type A. Broilers on a 4 phase feeding program were fed diets containing either a standard metabolizable energy (ME) (100%) or a reduced ME (98%) level. The test probiotic was compared to an un-supplemented negative control and a commercial benchmark product as positive control over a 35 D feeding trial, using a 2 × 3 factorial experimental design. Chicks were inoculated with a once-off dose of C. perfringens on day 14. Growth performance was measured weekly to calculate body weight (BW), feed intake (FI) and feed conversion ratio (FCR). Villi histomorphology, gut lesions, and liver weight were assessed at day 35. Broilers fed the reduced ME diet with the test probiotic achieved higher final BWs (P = 0.037) and FCR (P = 0.014) than the negative control. Broilers fed the standard ME diet with the test probiotic showed improved (P = 0.001) FCR than the negative control from day 21 onwards. Increased duodenal villi height (P = 0.012) and villi height to crypt depth ratio in the duodenum (P < 0.0001) and jejunum (P = 0.0004) were observed in broilers fed the reduced ME diet containing the test probiotic. Additionally, the test probiotic resulted in significantly reduced relative liver weights in both ME groups. Consequently, the results suggest that the novel multi-strain Bacillus based probiotic enhanced broiler performance and improved gut health and is thus attractive as an alternative to AGP's in broiler production.

The Efficiency of Xylanase in Broiler Chickens Fed with Increasing Dietary Levels of Rye

In this paper, we present a study on the evaluation of the effect of xylanase addition to a diet with an increasing content of modern hybrid rye (Brasetto variety) on the performance indices and viscosity of small intestine content in broiler chickens. A total of 560 1-day-old male Ross 308 chickens were randomly assigned to 1 of 10 treatments, each comprising 7 replicate cages, with 8 male birds per cage. A 5 × 2 factorial arrangement was employed, with five dietary levels of ground rye (0%, 5%, 10%, 15%, and 20%). All the diets were either unsupplemented or supplemented with xylanase (200 mg/kg of feed; with minimum xylanase activity 1000 FXU/g). In the starter rearing period (1⁻21 days of age), the inclusion of rye (without xylanase supplementation) to the diet, even at the lowest dietary level (5%), negatively affected body weight gain (p < 0.05); there was no effect on feed intake and feed conversion ratio. In older chickens (the grower-finisher rearing period; 22⁻42 days of age), none of the dietary levels of rye (5⁻20%) affected growth performance indices. Similarly, no significant effect of increasing dietary level of rye was found for the entire rearing period (1⁻42 days of age). Diet supplementation with xylanase improved body weight gain and feed conversion ratio in chickens from 1 to 21 days of age. No positive effect of enzyme was found in older birds. No significant effects of the experimental factors used were noticed on the results of slaughter analysis, i.e., the carcass yield, breast meat yield, abdominal fat, and relative weight of the liver and gizzard. A high dietary concentration of rye (20%) increased the viscosity of small intestine content (p < 0.05); however, diet supplementation with xylanase significantly alleviated this effect. The findings of this experiment indicated that modern hybrid rye grain may be used at a 20% dietary level in broiler diets during the second feeding phase, i.e., from 22 to 42 days of age, without any detrimental influence on growth performance indices, while enzyme (xylanase) positively affected body weight gain and feed conversion ratio in younger chicks (1⁻21 days of age).

Alkaline Active Hemicellulases

Xylan and mannan are the two most abundant hemicelluloses, and enzymes that modify these polysaccharides are prominent hemicellulases with immense biotechnological importance. Among these enzymes, xylanases and mannanases which play the vital role in the hydrolysis of xylan and mannan, respectively, attracted a great deal of interest. These hemicellulases have got applications in food, feed, bioethanol, pulp and paper, chemical, and beverage producing industries as well as in biorefineries and environmental biotechnology. The great majority of the enzymes used in these applications are optimally active in mildly acidic to neutral range. However, in recent years, alkaline active enzymes have also become increasingly important. This is mainly due to some benefits of utilizing alkaline active hemicellulases over that of neutral or acid active enzymes. One of the advantages is that the alkaline active enzymes are most suitable to applications that require high pH such as Kraft pulp delignification, detergent formulation, and cotton bioscouring. The other benefit is related to the better solubility of hemicelluloses at high pH. Since the efficiency of enzymatic hydrolysis is often positively correlated to substrate solubility, the hydrolysis of hemicelluloses can be more efficient if performed at high pH. High pH hydrolysis requires the use of alkaline active enzymes. Moreover, alkaline extraction is the most common hemicellulose extraction method, and direct hydrolysis of the alkali-extracted hemicellulose could be of great interest in the valorization of hemicellulose. Direct hydrolysis avoids the time-consuming extensive washing, and neutralization processes required if non-alkaline active enzymes are opted to be used. Furthermore, most alkaline active enzymes are relatively active in a wide range of pH, and at least some of them are significantly or even optimally active in slightly acidic to neutral pH range. Such enzymes can be eligible for non-alkaline applications such as in feed, food, and beverage industries.This chapter largely focuses on the most important alkaline active hemicellulases, endo-β-1,4-xylanases and β-mannanases. It summarizes the relevant catalytic properties, structural features, as well as the real and potential applications of these remarkable hemicellulases in textile, paper and pulp, detergent, feed, food, and prebiotic producing industries. In addition, the chapter depicts the role of these extremozymes in valorization of hemicelluloses to platform chemicals and alike in biorefineries. It also reviews hemicelluloses and discusses their biotechnological importance.

Utility of acidic xylanase of Bacillus subtilis subsp. subtilis JJBS250 in improving the nutritional value of poultry feed

Cane molasses has been employed as a cost-effective medium for enhanced xylanase production in submerged fermentation. Bacillus subtilis subsp. subtilis JJBS250 produced xylanase (15.16 U/ml) at pH 4.0, 35 °C and 200 rpm after 54 h using optimized basal medium by 'one variable at a time approach'. Addition of Tween 80 and PEG 4000 also enhanced xylanase production in cane molasses medium. Combined effect of yeast extract, incubation time and PEG 4000 using statistical optimization enhanced xylanase production to 38.60 U/ml, which was 2.54-fold higher than the 'one variable at a time approach'. The efficacy of xylanase from Bacillus subtilis subsp. subtilis JJBS 250 was evaluated in the improvement of poultry feed nutrition. Xylanase addition (10 IU/g feed) enhanced liberation of reducing sugars (95.540 mg/g substrate) after 48 h at 60 °C. Optimization has resulted in enhanced production of xylanase that improved the nutritional quality of poultry feed.

The evolution and application of enzymes in the animal feed industry: the role of data interpretation

1. Enzymes have been used commercially for nearly 40 years and save significant costs through sparing of expensive nutrients but the mechanism by which this is achieved is still debated. 2. The research focused on non-starch polysaccharidase (NSPase) enzymes is used as an example of where greater progress could have been made if the details of the work had been described more fully and the analysis of the data generated had been broader in scope and more critical. 3. Lack of standardisation of the details presented in the materials and methods has been identified as a significant barrier to meaningful retrospective analysis and thus limits advances in the understanding of the mode of action of these enzymes. 4. The identity of the enzyme employed and its activity is often lacking, and more importantly the purity is rarely disclosed. Contaminant activities which are neither listed nor assayed could play a significant role in the responses observed. 5. The dose optimum of most enzymes is often considerably higher than that employed in most studies. Thus studies claiming synergy between two 'activities' should ensure that the response is not related to each enzyme simply augmenting the dose of just one activity in the finished feed. This is a common problem, and coupled with the lack of factorial experiments to justify the presence of each enzyme in a multi-enzyme product, it is not surprising that there is still debate as to whether single or multi-enzymes are best suited poultry rations. 6. The three proposed mechanisms for NSPases (viscosity, cell wall and prebiotic) are discussed, and along with their strengths and weaknesses it is suggested that a re-evaluation of each is needed. Viscosity may have to be re-evaluated as being a function not only of the cereal being fed, but of the age of the animal as well. The cell wall theory as described is poorly modelled in vitro and hence the validity of these data is questioned. The prebiotic theory may need significant modification as it appears that the quantities of oligomers produced are insufficient to generate the additional volatile fatty acids (VFA)'s reported. It is likely that all three mechanisms play a role in the responses observed, but the prebiotic mechanism probably plays by far the most important part in low viscosity diets. 7. Future research would be improved if it considered all potential mechanisms when designing a trial. Significant failings are apparent as a result of adherence to tenets in explanation of the results. Most importantly, it should be emphasised that a hypothesis is there to be tested, not defended.

Evaluation and Selection of Bacillus Species Based on Enzyme Production, Antimicrobial Activity, and Biofilm Synthesis as Direct-Fed Microbial Candidates for Poultry

Social concern about misuse of antibiotics as growth promoters (AGP) and generation of multidrug-resistant bacteria have restricted the dietary inclusion of antibiotics in livestock feed in several countries. Direct-fed microbials (DFM) are one of the multiple alternatives commonly evaluated as substitutes of AGP. Sporeformer bacteria from the genus Bacillus have been extensively investigated because of their extraordinary properties to form highly resistant endospores, produce antimicrobial compounds, and synthesize different exogenous enzymes. The purpose of the present study was to evaluate and select Bacillus spp. from environmental and poultry sources as DFM candidates, considering their enzyme production profile, biofilm synthesis capacity, and pathogen-inhibition activity. Thirty-one Bacillus isolates were screened for in vitro relative enzyme activity of amylase, protease, lipase, and phytase using a selective media for each enzyme, with 3/31 strains selected as superior enzyme producers. These three isolates were identified as Bacillus subtilis (1/3), and Bacillus amyloliquefaciens (2/3), based on biochemical tests and 16S rRNA sequence analysis. For evaluation of biofilm synthesis, the generation of an adherent crystal violet-stained ring was determined in polypropylene tubes, resulting in 11/31 strains showing a strong biofilm formation. Moreover, all Bacillus strains were evaluated for growth inhibition activity against Salmonella enterica serovar Enteritidis (26/31), Escherichia coli (28/31), and Clostridioides difficile (29/31). Additionally, in previous in vitro and in vivo studies, these selected Bacillus strains have shown to be resistant to different biochemical conditions of the gastrointestinal tract of poultry. Results of the present study suggest that the selection and consumption of Bacillus-DFM, producing a variable set of enzymes and antimicrobial compounds, may contribute to enhanced performance through improving nutrient digestibility, reducing intestinal viscosity, maintaining a beneficial gut microbiota, and promoting healthy intestinal integrity in poultry.

Impact of combined β-glucanase and xylanase enzymes on growth performance, nutrients utilization and gut microbiota in broiler chickens fed corn or wheat-based diets

The effects of a xylanase and β-glucanase (XB) blend (2,500 U of xylanase and 250 U of β-glucanase per kg of complete feed) on growth performance, nutrients utilization and digesta microbiota in broiler chickens were investigated. A total of 140 day-old male Ross 308 broiler chicks were randomly assigned to 7 replicate cages and fed experimental diets. Diets were based on either corn or wheat without or with supplemental XB. Performance was monitored weekly and excreta were collected from d 17 to 20 for nutrients digestibility and AMEn measurements. On d 21, jejunal contents were collected for viscosity determination whereas ileal and cecal contents were obtained for microbial analysis by Illumina sequencing. Microbial data were analyzed using QIIME and PLS-DA whilst other data were analyzed using SAS. Birds fed wheat diets had higher (P < 0.001) BWG (3.4%) than birds fed corn-based diet whilst birds fed XB had better BWG (4%) and FCR (7%) than birds fed non-XB diets. Birds fed wheat diet had higher (P < 0.001) NDF (46.5%) and less (P = 0.01) CP (-5.4%) digestibility compared to birds fed corn-based diet. XB reduced (P < 0.001) jejunal digesta viscosity to a greater extent in wheat diet (-31%) than in corn-based diet (-10%). Birds fed wheat-based diet with XB had higher (3.5%) starch digestibility than birds fed this diet without XB. Janthinobacterium was associated with non-XB corn-based diet, whereas Ruminococcus, Lachnospiraceae, Lactobacillaceae, Peptostreptococcaceae, Clostridiales, Acidovorax and Blautia were associated with XB corn-based diet in the ileum. A relatively similar microbiome clustering was observed in wheat-based treatments in the cecum. There were no significant (P ≥ 0.05) correlations between selected ileal or cecal bacterial taxa and AMEn. Diet impacted growth performance but XB was efficacious across diet types, implying that degradation of dietary fibrous components by feed enzymes may stimulate performance in young birds. Data provided significant insight on ileal and cecal microbial profile associated with the dietary types and XB; however their functional roles require further investigations.

Considerations on the use of exogenous fibrolytic enzymes to improve forage utilization

Digestion of cell wall fractions of forage in the rumen is incomplete due to the complex links which limit their degradation. It is therefore necessary to find options to optimize the use of forages in ruminant production systems. One alternative is to use exogenous enzymes. Exogenous fibrolytic enzymes are of fungal or bacterial origin and increase nutrient availability from the cell wall, which consists of three fractions in different proportions depending on the species of forage: digestible, potentially digestible, and indigestible. The response to addition of exogenous enzymes varies with the type of forage; many researchers infer that there are enzyme-forage interactions but fail to explain the biological mechanism. We hypothesize that the response is related to the proportion of the potentially digestible fraction. The exogenous enzyme activity depends on several factors but if the general conditions for enzyme action are available, the potentially digestible fraction may determine the magnitude of the response. Results of experiments with exogenous fibrolytic enzymes in domestic ruminants are inconsistent. This, coupled with their high cost, has made their use unattractive to farmers. Development of cheaper products exploring other microorganisms with fibrolytic activity, such as Fomes fomentarius or Cellulomonas flavigena, is required.

Multicarbohydrase Enzymes for Non-ruminants

The first purpose of this review is to outline some of the background information necessary to understand the mechanisms of action of fibre-degrading enzymes in non-ruminants. Secondly, the well-known and understood mechanisms are described, i) eliminating the nutrient encapsulating effect of the cell wall and ii) ameliorating viscosity problems associated with certain Non Starch Polysaccharides, particularly arabinoxylans and β-glucans. A third, indirect mechanism is then discussed: the activity of such enzymes in producing prebiotic oligosaccharides and promoting beneficial cecal fermentation. The literature contains a wealth of information on various non starch polysaccharide degrading enzyme (NSPase) preparations and this review aims to conclude by discussing this body of work, with reference to the above mechanisms. It is suggested that the way in which multi- versus single-component products are compared is often flawed and that some continuity should be employed in methods and terminology.