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Research Article

Maintenance Energy Requirements in Modern Broilers Fed Exogenous Enzymes

J.V. Caldas, K.M. Hilton, N. Boonsinchai, G. Mullenix, J.A. England and C.N. Coon
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Objective: The objective of this study was to determine if exogenous enzymes reduce the metabolizable energy requirements for maintenance in broilers. Materials and Methods: Two feeds were tested, a negative control and negative control plus enzyme composite. The composite was a proprietary blend of glucanase + xylanase + cellulase + arabinofuranosidase + protease + phytase. Feed allowances were 30-100% of the ad libitum feed intake from 16-27 days. The retained energy in the carcass was evaluated as protein gain, g×5.45 kcal g–1+fat gain×8.95 kcal g–1. A linear regression of Y = Retention energy kcal/kg0.70 was regressed by X = Metabolizable energy intake kcal/kg0.70 where the metabolizable energy intake at zero carcass retention energy was the metabolizable energy of maintenance. Results: Body weight gain was +6.39 g day–1 with the enzyme treatment at ad libitum intake. The metabolizable energy for maintenance was 168±4.2 kcal/kg0.70 (R2 = 0.98) for the enzyme treatment and 160±4.5 kcal/kg0.70 (R2 = 0.98) for the control (p<0.01). The efficiency of energy utilization for maintenance and tissue gain was improved by 4 and 3%, respectively with the enzymes. The enzyme had -7.6 kcal/kg0.70 metabolizable energy of maintenance which represents 4.5% lower (p<0.01) than the control. Energy savings from the enzyme composite ranged from 67 kcal kg–1 at ad libitum intake to 238 kcal kg–1 at 30% intake. Conclusion: The present study showed that the enzyme composite reduced the broiler energy requirement for maintenance and improved the efficiency for protein gain. To the authors’ knowledge, this is the first research reporting that an enzyme composite decreases the maintenance energy and changes the tissue efficiency gain. Further investigation is required.

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J.V. Caldas, K.M. Hilton, N. Boonsinchai, G. Mullenix, J.A. England and C.N. Coon, 2022. Maintenance Energy Requirements in Modern Broilers Fed Exogenous Enzymes. International Journal of Poultry Science, 21: 107-118.

DOI: 10.3923/ijps.2022.107.118

Copyright: © 2022. This is an open access article distributed under the terms of the creative commons attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.


The poultry industry keeps improving the performance response and nutrient utilization of the broiler even when meat quality remains an issue1. Current and future studies will support the continuous improvement in the sustainability of poultry production. Energy remains the most expensive component of broiler feeds and maintenance energy requirements is a large component, being 42-44% of the energy intake2. Maintenance energy requirements include basal metabolism, thermogenesis and physical activity. Maintenance energy requirements need to be satisfied before tissue gain occurs3, therefore, a reduction in the maintenance requirement will enable the animal to derive more nutrients for tissue gain or production. The addition of exogenous enzymes such as phytases, proteases, carbohydrases individually or in combination to poultry diets has been reported to improve performance and nutrient digestibility4-9. The partitioning of additional feed energy from enzymes into maintenance and production as well as the specific mechanisms involved in the energy savings is unclear. A better understanding of partitioning and energy saving mechanisms could explain the inability to measure a consistent response of exogenous enzymes in corn-soybean meal based diets10. Exogenous enzymes in poultry diets have been shown to decrease heat production (HP) using an indirect calorimetry system11. Based on maintenance energy being the largest component of HP, it is possible that enzymes could decrease this component. Metabolizable energy (ME) is the most common energy system for formulating poultry diets and normally feed intake is subject to ME concentration in the feed12. Maintenance energy requirement is defined as the requirement at zero tissue gain at normal physiological processes and health13,14. The ME maintenance requirement is determined from the intersection of the regression line for ME intake with the zero energy retention line15, the linear regression of energy balance is fit between retained energy (RE) (RE = Y) and ME intake (MEI = X). The hypothesis of this study was to determine if adding this specific enzyme composite changes the metabolizable energy of maintenance and energy efficiencies for tissue gain in modern broilers.


The University of Arkansas, Institutional Animal Care and Use Committee (IACUC) No. 12041 approved all management practices and procedures.

Birds, management and diets: Five hundred 1 day-old Cobb male broilers (Cobb Fayetteville, Arkansas hatchery) were reared in floor pens until day 15. On day 16, three hundred and eighty four broilers with initial BW of 449 g±27 sd (6.0% CV) were allocated to 96 wire metabolic cages (dimensions of each cage was 91×30 cm) with four broilers per cage. Temperature was reduced from 33°C for day 1 of age to 22°C at day 27. The lighting program was 23 hrs light: 1 hr dark. Two dietary treatments were tested. Diet 1: Negative control (NC) and Diet 2: NC+enzyme composite (NC+Enz). This proprietary enzyme composite (Victus®) included six different exogenous enzymes: (1) Glucanase produced from fermentation of Aspergillus aculeatus, (2) Xylanase produced from Trichoderma longibrachiatum, (3) Cellulase produced from Trichoderma longibrachiatum, (4) Arabinofuranosidase produced from Trichoderma longibrachiatum and Aspergillus aculeatus, (5) Serine protease with a chymotrypsin specificity from Nocardiopsis prasina (donor microorganism) expressed in Bacillus licheniformis (host or production microorganism), (6) Phytase from Aspergillus oryzae (Table 1). To make the NC+Enz treatment, the enzyme composite was added on-top at the rate of 350 g MT–1 to the basal Grower diet formulated with corn and soybean meal-based diet to have −100 kcal kg–1 and same amino acids and minerals as the 2018 Cobb 500 recommendations (Table 2). The negative control (NC) feed was mixed again to avoid differences on mixing between the two treatments. The basal diet contained 500 FYT kg–1 phytase activity with contributions of 0.10% Ca and 0.10% avP, so the added 1400 FYT kg–1 of phytase in the enzyme composite treatment was on-top and it did not have matrix contributions for minerals nor for amino acids.

Prior to the experimental period, the NC+Enz birds were adapted to the enzyme composite by being fed the same enzyme composite during the starter period (1-15 day) at the rate of 375 g MT–1, however broilers were selected to have the same initial body weight between treatments on day 16. From 16-27 day of age, each diet was fed at eight controlled feeding levels: 30, 40, 50, 60, 70, 80, 90 and 100% of ad libitum consumption with 6replications per treatment. The amount of feed was increased daily for 11 days (16-27 day) based on feed intake of the ad libitum group. Samples of each diet were sent for enzyme analysis verification to a commercial enzyme laboratory (TMAS, DSM Nutritional Products, Belvidere, NJ) (Table 3).

Chemical analysis: The analysis of AMEn was evaluated for the ad libitum group of the control treatment. The AMEn involved analysis of gross energy, dry matter and nitrogen in feed and excreta. Gross energy (GE) was determined with a bomb calorimeter (Parr 6200 bomb calorimeter, Parr Instruments Co., Moline, IL.). Dry matter was analyzed by method 934.0116 and nitrogen determined by the method 990.0317. The AMEn assay was determined by the classical total excreta collection method. The broilers underwent an adaptation to the experimental diets for 4 days (16-20 day) before excreta collection for 3 days. On the third day of collection, the excreta collections were pooled within a metabolic cage, mixed and a representative sample (120 g) was lyophilized in a freeze dryer. The lyophilized excreta samples were ground with a commercial grinder to pass through a 0.5 mm sieve. Samples were sent to the Central Laboratory at the University of Arkansas for analysis (dry matter, gross energy and nitrogen).

Body composition analysis: Broilers were analyzed for whole body composition at 16 and 27 day using the dual energy X-ray absorptiometry (DEXA). The body of 20 broilers of the same initial weight were scanned on day 16 to have the initial body protein, body fat and body mineral composition. At 27 day, broilers were humanely sacrificed by CO2 inhalation. All 360 broilers were scanned individually by DEXA for body composition analysis. The DEXA values were adjusted using the feed restricted broiler equations as described by Caldas11. Briefly, the equations are:

Body protein:

g = 0.149×DEXA Lean g1.02

Body fat:

g = -15.9+0.095×DEXA tissue, g+0.28×DEXA fat, g-0.468×DEXA area, cm2

Body mineral:

g = e[1.73+0.51×Ln(Dexa BMC, g)]

Calculations: Body weight gain and feed conversion ratio (FCR) were calculated from 16-27 day, taking initial and final body weights. The FCR was accounted as 1 point for every 0.01 g g–1 value. The AMEn in the feed was calculated according to the equation by Hill and Anderson18:


AMEn = Apparent metabolizable energy, nitrogen corrected
Ged = Gross energy in the diet (kcal kg–1)
FI = Feed intake (kg)
Exc = Excreta output (kg)
Nd = Nitrogen in the diet (g g–1)
Nexc. = Nitrogen in the excreta (g g–1)

MEI (metabolizable energy intake, kcal/kg0.70) was calculated as:

MEI = FI (kg)×2966 kcal/kg/av. BW, kg0.70

AMEn = 2966 was the result of the energy evaluation in the feed.

The body compositions for protein, fat and bone mineral content (BMC) were reported as dry matter (DM) g kg–1 of body weight.

RE (retained energy, kcal/kg0.70) was calculated as described by Caldas et al.19:

Retained fat (RF) and protein (RP) (g day–1) were calculated as the fat and protein at 27 day minus the tissue composition at 16 day. When fitting the linear regression of Y = Retained fat or protein vs X = Feed intake (FI) g day–1, tissue retention for each treatment were calculated with the equation RF = -5.35+0.0934×FI -0.107 when calculating for the NC and +0.107 for the NC+Enz treatment (Fig. 2). {NC»-0.107, NC+Enz. »+0.107, else»} means that when no enzyme composite is added to the diet the equation subtracts 0.107 and when enzyme is added, the equation adds 0.107.

In similar manner, retained protein was calculated as RP = -0.29+0.107×FI -0.103 for NC and+0.103 for NC+Enz (Fig. 3). The slope of both equations in Fig. 2 and 3 is the tissue retention (fat or protein) g g–1 feed allowance and the intercept (first value of the equation) it is the value of fat or protein retention when feed intake is zero.

HP (Heat production) kcal/kg0.70 was calculated to be = MEI-RE.

Av.BW0.70 was the average metabolic body weight from the initial and final body weight of the feeding study elevated to the power of 0.7020.

The energy value of the enzyme composite (kcal kg–1) or matrix in the formulation was calculated by MEm (NC+Enz) minus MEm (NC) divided by the actual FI in each phase of feed restriction.

Statistical analysis: For all parameters, the experimental unit was one cage, only clarifying that for body composition the average of four broilers within each cage was pooled to make one replicate. The body weight gain (BWG), FCR and body composition data means were analyzed by ANOVA within each feed allowance level and initial body weight was included as a covariate, the means were separated by t-student and p-value was considered significant when p≤0.05. Body composition (g kg–1) was also analyzed by a 2×8 factorial design (diet×feed allowance) with initial body weight as covariate. The means of feed allowance means were separated by Tukey HSD (honestly significant difference) test and p -value was considered significant when p≤0.05. Fat and protein retention (g day–1) was fitted against g day–1 FI as a multiple linear regression (MLR), having FI and diet in the X-axis and fat or protein retention in the Y-axis. For the determination of MEm, a MLR analysis was performed including the diet effect to obtain the difference of MEm between diets. Retained energy (RE) as the dependent variable was regressed on metabolizable energy intake (MEI) adding the diet effect in the X-axis, as part of the equation according to Farrell15. The MEm was calculated by inverse prediction when RE = zero (0) for NC and NC+Enz. Another linear regression was fitted separately by diet and the slope of the equation was used for determining efficiency of energy utilization for gain (kg). A logarithmic curve was fitted between HP by MEI building parameters for:



a = NEm (net energy of maintenance)

The efficiency of energy utilization of maintenance (km) was calculated with the ratio NEm/MEm13. All data were analyzed using JMP15.221.


The enzyme analysis in the feed from the experimental period resulted in 75-129% of the calculated inclusion levels showing the expected units of enzymes were in the experimental feed NC+Enz (Table 3).

Body weight gain (BWG), FCR and body composition: Body weight gain from 16-27 day was +2.02 g day–1 and +6.39 g day–1 for NC+Enz was significantly improved (p<0.05) for NC at 60% and 100% feed allowance, respectively. There was a tendency of higher BWG with NC+Enz at 40% feed allowance (p = 0.065) and 80% feed allowance (p = 0.063) (Table 4). The FCR was significantly better for NC+Enz at 40% (-22 points), 60% (-10 points) and 100% (-11 points) of feed allowance (p<0.05) and tendency to be better at 70% (-8 points) and 80% (-8 points) feed allowance (p = 0.089 and 0.078, respectively). The body fat composition (g kg–1) was higher for the NC+Enz treatment (NC+Enz: 182 vs NC: 162 g kg–1 DM) only at 50% feed allowance (p = 0.044) (Table 5) and the difference across all feed allowances was not significant (p>0.05) (Table 6). As feed allowance increased from 30-100%, the fat component in the body of the broilers increased from 140-304 g kg–1 (p<0.01), the fat for broilers fed ad libitum was more than twice the fat amount for broilers fed at 30% feed allowance (Table 6). The body protein composition (g kg–1) was lower for the NC+Enz treatment (NC+Enz: 613 vs NC:616 g kg–1) at 60% feed allowance (p = 0.025) and a tendency of lower body protein at 70% feed allowance (p = 0.079) (Table 5). Protein between diets across all feed allowances was not different (p>0.05) (Table 6). As feed allowance increased from 30-100%, body protein decreased from 643-589 g kg–1(p<0.01) but the difference was not as large as the change in body fat composition (Table 6).