Effect of dietary β-mannanase supplementation on growth performance and nutrient retention in broiler chickens fed corn-soybean meal-based diets with low energy and amino acid density

Abstract

The present study was conducted to evaluate the effect of two different β-mannanases on growth performance and nutrient retention of broiler chickens fed a diet with low energy and amino acid density. A total of 312 one-day-old male broiler chickens (Ross 308) were placed in floor pens and fed a standard starter diet for 16 days. They were then randomly moved to stainless steel cages and distributed into three groups, with 13 replicates of 8 chickens each. The control group received a corn-soybean meal-based grower diet with reduced metabolizable energy by ∼100 kcal/kg and a 10-12% reduction of digestible amino acids (lysine, methionine, and threonine). Titanium oxide was added at 0.5% of diet as an indigestible marker. The other groups were fed the same diet supplemented with either β-mannanase A derived from Thermothelomyces thermophilus (100 g β-mannanase/MT grower diet) or β-mannanase B derived from Paenibacillus lentus (350 g β-mannanase/MT grower diet). The trial lasted for 7 days from d 17 to d 23, comprising 4 days of acclimatization followed by 3 days of sample collection. Final body weight (d 23), body weight gain (d 17-23), and feed intake (d 17-23) of broiler chickens did not differ among the groups. However, both β-mannanases significantly improved the feed conversion ratio during d 17-23 (P = 0.039) and nitrogen retention (P = 0.028) in broiler chickens compared to the control group. Moreover, dietary supplementation with β-mannanase A significantly increased dry matter retention (P = 0.050), organic matter retention (P = 0.028), and nitrogen-corrected apparent metabolizable energy (AMEn; P = 0.033) compared to the control group. In conclusion, supplemental β-mannanase, regardless of the product, improved the growth performance of broiler chickens by improving nutrient retention and dietary AMEn.

Introduction

Agro-industrial byproducts or plant-based energy and protein sources are integral constituents of poultry diets. However, a significant portion of these byproducts remains undigested and ends up in the excreta, largely due to the complex carbohydrates in plant cell walls, collectively termed as fiber. Simple carbohydrates and starch are readily digested, while oligosaccharides are fermented, leaving behind complex polysaccharides such as cellulose, hemicellulose, and pectin. These structural carbohydrates, commonly referred to as non-starch polysaccharides (NSP), undergo fermentation to a much lesser extent (Shastak et al., 2015). Hemicellulose is a neglected fiber fraction in the formulation of poultry diets, often misconstrued as a single entity. However, it comprises various polysaccharides including β-mannans. β-mannans consist of a β-1,4-linked backbone of D-mannose or residues of both D-glucose and D-mannose, with different side chains creating four distinct types namely linear mannan, galactomannan, glucomannan, and galactoglucomannan (Liepman et al., 2007). These β-mannans act as anti-nutrients and are known to induce physiological effects that are believed to be linked to gut inflammation (Kiarie et al., 2021). Mannans are the second most abundant hemicellulosic polysaccharides in nature, making mannanases the second most important enzyme for hydrolyzing hemicellulose (Shastak et al., 2015). Soybean meal (SBM), a primary protein source in poultry diets worldwide, typically contains 1 to 3% β-mannans (Kiarie et al., 2021). The complete breakdown of β-mannans can release simple carbohydrates (sugar subunits in β-mannans, D-mannose), potentially providing additional energy. However, poultry can only partially utilize D-mannose as an energy source (Shastak et al., 2015). Additionally, poultry lack the endogenous enzymes needed to digest mannans, leading to a loss of both energy and protein, as these complex carbohydrates bind with proteins in the plant cell wall. Exogenous endoenzyme β-mannanase (1,4-β-D-mannan mannohydrolase, EC 3.2.178) cleaves the β-1,4-linked mannan backbone, releasing β-1,4-manno-oligosaccharides. Further breakdown into subunits requires exoenzymes such as β-mannosidase (1,4-β-D-mannopyranoside hydrolase, EC 3.2.1.25), β-glucosidase (1,4-β-D-glucoside glucohydrolase, EC 3.2.1.21), acetyl mannan esterase (EC 3.1.1.6), and α-galactosidase (1,6-α-D-galactoside galactohydrolase, EC 3.2.1.22) (Moreira and Filho, 2008). Recent findings have shown that β-mannanase is active at the cell wall but also intracellularly in soybean meal, potentially improving the accessibility for endogenous enzymes to their substrate (Rueckel et al., 2024). Therefore, supplementing poultry diets with exogenous β-mannanase enzymes can improve nutrient utilization and potentially provide additional dietary energy, as these enzymes cleave the β-1,4-linked backbone of mannans, releasing D-mannose that can be partially used as an energy source along with bound cell wall components (Moreira and Filho, 2008). Given these facts, we hypothesized that supplementing commercial β-mannanases in corn-SBM-based broiler diets with low energy and amino acid density may improve growth performance by enhancing nutrient retention.

Materials and methods

This project was approved and conducted under the guidelines of the Institutional Animal Care and Use Committee. The study was designed as a randomized complete block with three groups: control (without β-mannanase), β-mannanase A derived from Thermothelomyces thermophilus (100 g β-mannanase/MT grower diet), and β-mannanase B derived from Paenibacillus lentus (350 g β-mannanase/MT grower diet). A total of 312 one-d-old male Ross 308 chickens were distributed into three groups, each consisting of 13 replicates with 8 chickens per replicate. Stainless steel cages were used, with each cage serving as a replicate. The chickens were raised under standard management conditions according to the Aviagen guidelines for Ross 308 broilers. The birds were fed ad libitum in two phases: starter (d 0-16) and grower (d 17-23) phases. Corn-SBM-based mash diets were prepared to meet the dietary recommendations for Ross 308 broiler chickens for starter phase. Approximately 100 kcal/kg metabolizable energy along with 10-12% digestible amino acid (lysine, methionine, and threonine) density was reduced in all the grower diets compared to the Ross 308 nutrient recommendation (Table 1). Inclusion levels of synthetic amino acids were adjusted to reduce the digestible amino acid density. β-Mannanases, sourced from different manufacturers, were incorporated into the grower diets based on each supplier's specific guidelines. Additionally, titanium dioxide (TiO₂) at 0.5% of diet was added as an indigestible marker in grower diets. On d 17, all chickens were weighed and randomly distributed into the groups based on average body weight (BW). A 7-d total tract retention trial was conducted from d 17-23, consisting of a 4-d acclimatization period followed by a 3-d excreta collection period. All the birds showed optimum health signs, and no mortality occurred throughout the study.

Table 1.

Dietary ingredients and nutrient composition (%, as fed basis).

	Starter (d 0-16)	Grower (d 17-23)4
Ingredients
Corn	58.072	61.696
Soybean meal	37.100	34.500
Soybean oil	1.500	1.000
Limestone	0.945	0.640
Dicalcium phosphate	1.120	0.760
DL-Methionine	0.315	0.209
L-Lysine HCL	0.195	0.045
L-Threonine	0.093	–
Sodium bicarbonate	0.200	0.200
Salt	0.250	0.240
Vitamin premix1	0.100	0.100
Mineral premix2	0.100	0.100
Phytase, 1000 FTU3	0.010	0.010
Titanium dioxide	–	0.500
Calculated nutrient composition (%)
Dry matter	87.97	87.81
Crude protein	23.05	21.45
AMEn, kcal/kg	3007	2956
Ca	0.96	0.75
Total P	0.77	0.69
Available P	0.48	0.42
Lys	1.42	1.12
Digestible Lys	1.28	1.06
Met + Cys	1.06	0.91
Digestible Met + Cys	0.95	0.81
Thr	0.98	0.83
Digestible Thr	0.86	0.71
Linoleic acid	2.03	1.81
Ether extract	3.63	3.45
Crude ash	5.36	4.54
Crude fiber	2.57	2.65
Starch	37.78	40.03
Sugar	4.59	3.16
Analyzed nutrient composition (%)
Dry matter	–	87.5
Crude ash	–	4.75
Crude protein	–	20.78
Neutral detergent fiber	–	9.93
Gross energy, kcal/kg	–	3914.5

¹Provided per kilogram of complete diet: vitamin A, 15,000 IU; vitamin D3, 5,000 IU; vitamin E, 100 mg; vitamin K3, 3 mg; thiamine, 5 mg; riboflavin, 8 mg; pyridoxine, 5 mg; pantothenic acid, 16 mg; niacin, 60 mg; folic acid, 2 mg; biotin, 200 µg; vitamin B12, 20 µg.

²Provided per kilogram of complete diet: Cu, 16 mg; I, 1.5 mg, Co, 500 µg; Se, 350 µg; Fe, 60 mg; Zn, 100 mg; Mn, 120 mg; Mo, 1 mg.

³Full nutrient matrix was applied to both diets (Natuphos E 10000).

⁴The recommended nutrients levels for grower phase: energy 3050 kcal/kg, dig. Lys 1.18%, dig. Met+Cys 0.92%, dig. Thr 0.79%.

Excreta were collected in trays placed underneath the wired mesh floor of the cages, freeze-dried, and stored at −20°C until analysis. On d 23, all chickens and remaining feed were weighed to calculate body weight gain (BWG), feed intake (FI), and feed conversion ratio (FCR). The concentrations of TiO₂ in grower diets and excreta samples were analyzed using UV spectrophotometric method (Short et al., 1996). Furthermore, diets and excreta were analyzed for dry matter (DM), nitrogen (Kjeldahl method), and ash according to the methods described by Association of Official Analytical Chemists (AOAC). The neutral detergent fiber (NDF) content of diet and excreta samples was determined using the Van Soest method. Gross energy (GE) of the diet and excreta was analyzed by combustion using a bomb calorimeter (Parr 1241 Adiabatic Oxygen Bomb Calorimeter, Parr, Illinois, US). Total tract retention for DM, organic matter (OM), and NDF was calculated using the formula:

$$\text{Nutrient}\text{retention},\%=100-\left(100\times \frac{\text{Marker}\text{in}\text{diet}}{\text{Marker}\text{in}\text{excreta}}\times \frac{\text{Nutrient}\text{in}\text{excreta}}{\text{Nutrient}\text{in}\text{diet}}\right)$$

The apparent metabolizable energy corrected for nitrogen (AMEn) was calculated as follows:

$$\begin{array}{ccc}\hfill \text{AMEn},\text{kcal}/\text{kg}& =& \mathrm{G}{\mathrm{E}}_{\mathit{diet}}-\mathrm{G}{\mathrm{E}}_{\mathit{excreta}}\times \left(\frac{\text{Marker}\text{in}\text{diet}}{\text{Marker}\text{in}\text{excreta}}\right)\hfill \\ & & -8.22\times \left({\mathrm{N}}_{\mathit{diet}}-{\mathrm{N}}_{\mathit{excreta}}\right)\times \left(\frac{\text{Marker}\text{in}\text{diet}}{\text{Marker}\text{in}\text{excreta}}\right)\hfill \end{array}$$

Where

• GE = gross energy; N = nitrogen; 8.22, a factor representing the energy value of retained nitrogen.

One-way analysis of variance was applied to assess the effect of dietary β-mannanases on growth performance and nutrient retention of broiler chickens fed diets with low energy and amino acid density. Tukey's test was used as a post hoc to separate the significantly different means. Additionally, Pearson correlation analysis was conducted to evaluate the strength and direction of the relationship between DM, OM, and NDF retention with the AMEn of the diet. Differences were considered significant at a 95% probability level (P ≤ 0.05). Results were presented as mean ± standard error (pooled). All statistical procedures were conducted using a computer-based statistical software JMP (Pro 17; SAS Institute Inc., Cary, NC, US).

Results and discussion

Growth performance and nutrient retention of broiler chickens fed β-mannanase supplemented diets with reduced metabolizable energy and amino acid density are presented in Table 2. Despite no differences in final BW, BWG, and FI, β-mannanase supplementation significantly improved the FCR compared to the control group (P = 0.039). The retention of DM, OM, and dietary AMEn was significantly higher in β-mannanase A supplemented group compared to control (P ≤ 0.05). Nitrogen retention was significantly higher in β-mannanases, regardless of the product, supplemented groups than control group (P = 0.033). Furthermore, regression analysis revealed strong positive correlations between OM and DM retention and AMEn values (P < 0.0001, r = 0.764 and P < 0.0001, r = 0.729, respectively), as well as between NDF retention and AMEn values (P < 0.0001, r = 0.691).

Table 2.

Effect of dietary β-mannanase supplementation on growth performance and nutrient retention of broilers fed diets with low energy and amino acid density¹.

	Dietary Treatments2			Statistics
Item3	Control	β-mannanase A	β-mannanase B	SEM	P-value
Growth Performance
Initial BW (d 17)	682.9	683.0	682.7	1.95	0.998
Final BW (d 23)	1112	1128	1121	4.50	0.369
BWG (d 17-23)	429.4	445.1	437.9	3.52	0.194
FI (d 17-23)	684.7	690.2	679.3	2.81	0.294
FCR (d 17-23)	1.597a	1.552b	1.553b	0.01	0.039
Nutrient retention
Dry Matter, %	71.74b	72.80a	72.30ab	0.18	0.050
Organic Matter, %	73.90b	74.96a	74.47ab	0.16	0.019
Nitrogen, %	64.98b	66.50a	66.75a	0.30	0.028
NDF, %	37.34	38.01	36.12	0.51	0.317
AMEn, kcal/kg	3342b	3403a	3361ab	10.10	0.033

^a,bMeans with different superscripts in the same row are significantly different (P < 0.05).

¹Control: birds fed a corn-soybean meal grower diet with reduced metabolizable energy by ∼ 100 kcal/kg and 10-12% reduction of digestible amino acids (lysine, methionine, and threonine); β-mannanase A: birds fed control diet supplemented with 100 g/MT β-mannanase derived from Thermothelomyces thermophilus; β-mannanase B: birds fed control diet supplemented with 350 g/MT β-mannanase derived from Paenibacillus lentus.

²Data represent mean values of 13 replicates per treatment. (for AMEn: n = 12)

³BW: Body weight; BWG: body weight gain; FI: feed intake; FCR: feed conversion ratio; NDF: neutral detergent fiber, AMEn: nitrogen-corrected apparent metabolizable energy

Soluble β-mannans, indigestible anti-nutritional factors, entrap nutrients and form a highly viscous digesta in the gut due to their β-1,4-linked structure. This high viscosity hinders nutrient utilization, leading to poor growth performance. It also increases water consumption as birds attempt to effectively mix the digesta. β-mannanase supplemented to birds’ diets cleaves the β-1,4 linkages in mannans, decreasing digesta viscosity and the subsequent need for excess water consumption (Daskiran et al., 2004; Shastak et al., 2015). Additionally, the presence of β-mannans in the diet can mimic pathogen-associated mannose residues, provoking a localized or systemic feed-induced immune response depending on the binding site with the epithelial cells (Kiarie et al., 2021). This immune activation diverts energy and resources from growth and nutrient absorption towards immune function, leading to reduced growth performance and nutrient utilization. Consistent with our findings, previous studies have confirmed that β-mannanase supplementation in low energy diets maintains the growth performance of broiler chickens compared to those fed non-supplemented control diets (Klein et al., 2015; Yaqoob et al., 2022). The nutrient retention data in the present study corresponded well with the FCR of broiler chickens fed β-mannanase supplemented diets with reduced ME and amino acid density. The significant positive correlations between DM, OM, and NDF retentions and dietary AMEn further suggest that supplemental β-mannanase enzymes effectively degraded the β-mannans present in the corn-SBM based diet, conserving AMEn and supporting better growth performance of broilers. Overall, these findings align with previous reports demonstrating improved growth performance and nutrient utilization in broilers fed β-mannanase supplemented diets, with or without energy reduction (Daskiran et al., 2004; Ferreira et al., 2016; Caldas et al., 2018; de Souza et al., 2023).

In conclusion, supplementation of β-mannanase in broiler diets with low ME and amino density enhances the growth performance by improving the nutrient retention. Nevertheless, additional research is warranted to explore prececal amino acid digestibility in normal energy and low energy diets.

Declaration of competing interest

The authors declare no conflicts of interest associated with this publication and no significant financial support that could influence the outcome.