Effects of β-mannanase-based enzyme in corn-soy and corn-soy-canola diets on broiler performance

Abstract

A 2 × 2 factorial experiment was conducted to evaluate the effects of dietary partial replacement of soybean meal (SBM) by canola meal (CM) with and without a β-mannanase-based enzyme on growth performance of broilers. A total number of 360 one-day-old broiler chicks were weighed and allocated to four iso-caloric and iso-nitrogenous diets, each of which had 9 pens of 10 chicks with the same number of both sexes. Starter, grower and finisher diets were offered to birds from 0 to 21 day, 22 to 42 day and 43 to 49 day of age, respectively. All experimental data were subjected to the general linear model procedure of SAS as a complete randomised design. Dietary partial replacement of SBM by CM decreased body weight (BW) of broilers on days 21, 42 and 49 of age. Dietary CM inclusion decreased and increased feed intake (FI) of broilers during starting and finishing periods, respectively. Broilers fed corn-SBM diet shown improved feed conversion ratio (FCR) in comparing to those fed corn-CM diet during all rearing periods. Dietary enzyme supplementation improved BW of birds on 21, 42 and 49 days of age. Dietary β-mannanase supplementation improved feed conversion ratio feed conversion ratio (FCR) during growing as well as whole periods; but FI of birds was not affected by enzyme. Dietary inclusion of CM increased the relative weights of gizzard, liver, pancreas, fat pad, duodenum, jejunum and ileum; however, the relative length of digestive tracts was increased in CM-included dietary group. The relative weights of gizzard, fat pad, liver, pancreas and digestive tracts were not affected by dietary enzyme supplementation. Litter pH on week 7 was higher in corn-SBM in comparing to corn-SBM-CM dietary group. In conclusion, broilers fed CM-included diets did not achieve similar performance compared to corn-SBM control group. Dietary β-mannanase supplementation improved performance of broilers fed corn-SBM- and/or corn-SBM-CM-based diets.

Keywords:

• soybean meal
• canola meal
• β-mannanase
• performance
• broilers

Introduction

The introduction of low glucosinolate rapeseed (canola) has made canola meal (CM) a suitable alternative to soybean meal (SBM) as a vegetable protein source in broiler diets; however, the low level of available energy, crude protein and lysine, and the increased level of indigestible carbohydrates of CM compared with SBM have made CM a less competitive alternative when used at high levels in broiler diets. The relatively, low level of available energy in CM is associated with high level of non-starch polysaccharides (NSP) which has low digestibility in poultry.

The major NSP components found in SBM and CM are pectic polysaccharides, which include rhamnogalacturonan with associated side chains consisting of arabinose, galactose and xylose residues. Other polysaccharides of SBM and CM are cellulose, xylans, arabinoxylans, xyloglucans and β-mannans (Meng and Slominski 2005). β-Mannan, a linear polysaccharide composed of repeating β-1-4 mannose and 1-6 galactose and glucose units attached to the β-mannan backbone, and its derivatives (β-galactomannan or β-gluco-mannan) are integral components of cell walls in all legumes (Horton 1997). The β-mannan content of SBM and CM is about 1.1 to 1.3% and 0.49%, respectively (Jackson et al. 2004).

β-d-mannanase is a fermentation product of Bacillus lentus and degrades β-mannans by endo-hydrolyase enzyme activity. The addition of β-mannanase to broiler diets containing 2% guar gum significantly reversed the growth depression caused by the guar gum (Daskiran and Teeter 2001).

Many attempts have been made to improve the utilisation of NSP of SBM and CM for poultry using different carbohydrase supplements. In some cases carbohydrase supplementation appears to be beneficial in improving NSP digestibility of CM (Kocher et al. 2000; Meng et al. 2005) and full-fat canola seed (Meng et al. 2006) and in enhancing NSP, protein and energy utilisation from corn-SBM diets (Douglas et al. 2000; Kocher et al. 2002). However, in the other studies no beneficial effect has been seen in improving growth performance of poultry (Kocher et al. 2000 2001; Meng and Slominski 2005; Mushtaq et al. 2007).

Although there is reports in the literature demonstrating performance improvement of laying hens’ fed β-mannanase supplemented corn-SBM-based diets (Wu et al. 2005), not many researches have been conducted to investigate effects of β-mannanase supplementation of corn-CM-based diets on broiler's performance. The objective of this study was to evaluate the effects of β-mannanase on growth performance of broilers fed on corn-SBM- and/or corn-SBM-CM-based diets.

Materials and methods

Experimental procedures were approved by the Department of Animal Science of Razi University, Kermanshah province, Iran for the care and use of animals for scientific purposes.

The β-mannanase enzyme was provided by ImEx Gulf, Inc. The potency of β-mannanase was 165 × 10⁶ U/kg. Three hundred and sixty straight run one-day-old Cobb 500 broiler were purchased from a local supplier, weighed, housed floor and allocated to four iso-energetic and iso-nitrogenous diets, each of which had 9 pens (replicates) of 10 chicks with the same number of both sexes. Any birds showing signs of ill health, injury or being in poor condition were discarded. The birds were given 23L: 1D during each 24-hour period throughout the trial. The trial terminated when the birds were 49 day of age.

Starter, grower and finisher diets were offered to birds from 0 to 21 day, 22 to 42 day and 43 to 49 day of age, respectively. Feed and water were provided ad-libitum throughout the experiment. For each feeding period, diets were calculated to be iso-energetic and iso-nitrogenous to meet the nutrient requirements recommended by the NRC (1994)) for broilers (Table 1). Treatments/replicate combinations were randomly allocated. Broilers’ BW was recorded for each replicate (as group and not individually) on days 0, 21, 42 and 49 of age and FI was measured over these periods. Mortality was recorded daily, and FCR was calculated per experimental unit as total feed intake (kg): total gain of live chickens (kg), for each feeding period. Feeds were analysed for crude protein, calcium and available phosphorus according to the methods of AOAC (2000). Composition of the CM used in this experiment was: dry matter (91%), crude protein (35.24%), ether extract (2.61%), crude fiber (11.02%), Ca (0.63%) and total phosphorous (1.08%).

Table 1.  Composition and calculated analysis of experimental diets (g/100g).

	Starter (days 0–21)				Grower (days 22–42)				Finisher (days 43–49)
	No enzyme		β-Mannanase		No enzyme		β-Mannanase		No enzyme		β-Mannanase
Ingredient	SBM^1	CM	SBM	CM	SBM	CM	SBM	CM	SBM	CM	SBM	CM
Corn	56.66	56.25	56.67	56.25	64.67	64.27	64.68	64.29	66.48	66.39	66.49	66.35
Soybean meal	33.72	23.40	33.75	23.43	26.78	16.47	26.81	16.49	18.46	15.02	18.48	15.04
Canola meal	–	15.00	–	15.00	–	15.00	–	15.00	–	5.00	–	5.00
Wheat bran	4.06	0.07	3.99	–	4.09	0.09	4.01	–	12.03	10.70	11.95	10.62
Sunflower oil	1.76	1.76	1.76	1.76	0.95	0.95	0.95	0.95	–	–	–	–
DCP^2	1.33	1.28	1.33	1.28	0.98	0.94	0.98	0.94	0.720	0.700	0.720	0.700
Oyster shell	1.23	1.10	1.23	1.10	1.32	1.19	1.32	1.19	1.20	1.16	1.20	1.16
Common salt	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50
Mineral premix^3	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25
Vitamin premix^4	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25
HCL-lysine	0.11	0.05	0.11	0.05	0.15	0.09	0.15	0.09	0.09	0.07	0.09	0.07
DL-methionine	0.13	0.09	0.13	0.09	0.06	0.01	0.06	0.01	0.02	—	0.02	—
β-mannanase	–	–	0.04	0.04	–	–	0.04	0.04	–	–	0.04	0.04
Calculated composition^5
ME^6 (Kcal/kg)	2850	2850	2850	2850	2900	2900	2900	2900	2800	2800	2800	2800
CP	20.48	20.48	20.48	20.48	18.13	18.13	18.13	18.13	15.75	15.75	15.75	15.75
Lysine	1.14	1.11	1.14	1.12	1.03	1.00	1.02	1.00	0.81	0.80	0.81	0.80
Methionine	0.44	0.44	0.44	0.44	0.34	0.34	0.34	0.34	0.28	0.28	0.28	0.28
Methionine + Cysteine	0.81	0.84	0.81	0.84	0.65	0.69	0.65	0.69	0.56	0.58	0.56	0.58
EE	4.13	4.30	4.13	4.30	3.65	3.82	3.65	3.82	3.03	3.09	3.07	3.09
CF	4.05	4.53	4.05	4.53	3.75	4.23	3.74	4.22	4.08	4.24	4.07	4.23
Calcium	0.88	0.88	0.88	0.88	0.82	0.82	0.82	0.82	0.70	0.70	0.70	0.70
Available P	0.39	0.39	0.39	0.39	0.32	0.32	0.32	0.32	0.26	0.26	0.26	0.26
^1SBM: Corn-soybean meal-based experimental diet, CM: Corn-soybean-canola meal-based experimental diet; ^2 DCP: Dicalcium phosphate; ^3The mineral premix supplied per kilogram of diet: zinc, 120 mg; manganese, 120 mg; iron, 80 mg; copper, 10 mg; iodine, 2.5 mg; cobalt, 1 mg; ^4The vitamin premix supplied per kilogram of diet: vitamin A, 12,500 IU; vitamin D3, 4000 IU; vitamin E, 66 IU; vitamin B12, 39.6 µg; riboflavin, 13.2 mg; niacin, 165 mg; d-pantothenic acid, 44 mg; menadione, 0.4 mg; folic acid, 3.3 mg; pyridoxine, 13.75 mg; thiamin, 6.66 mg; d-biotin, 0.28 mg; ^5Calculated composition based on NRC (1994) feed composition tables; ^6ME: metabolisable energy, CP: crude protein, EE: ether extract, CF: crude fiber.

To measure carcass traits two birds of each replicate (the same location per each pen) were randomly selected and slaughtered at seven week of age and the weight and length of digestive tracts (duodenum, jejunum, ileum and caeca) were measured. Liver, pancreas, gizzard were dissected and weighed, and their relative weights (g/100g live body weight) were calculated.

Broiler litter samples were collected from five various places of each pen when the birds reached 3, 5 and 7 week of age. Moisture percentage and pH of stored wet litters were measured in laboratory on the days of sampling.

Two-way factorial ANOVA was applied for all measured parameters:

where Yijk = tested parameter of a broiler fed a diet containing SBM or CM i and with or without β-mannanase j; Ai = diet type (SBM or CM); Bj = β-mannanase addition (none, 0.4 g/kg diet); (A ·B)ij = interaction between diet type and enzyme addition; eijk =error term.

All experimental data were subjected to the GLM procedure of SAS (SAS Institute 2005) as a complete randomised design. All statements of significance are based on a probability of less than 0.05. The mean values were compared by Duncan's Multiple Range Test.

Results and discussion

The main effects of diet and enzyme on broiler growth performance (BW, FI and FCR) during weeks 1–7 are shown in Tables 2–5 –4, respectively. There was no interaction between diet and enzyme on any observed performance parameters during three rearing periods (P>0.05), except for BW on day 21 of age (P<0.01). Dietary partial replacement of SBM by CM decreased BW of broilers on days 21, 42 and 49 of age (P<0.01). Trend in replacing SBM by other plant or animal resources in poultry diets has been seen in literature because of high price of SBM and being an imported item in many countries. It has been shown that partial replacement of soybean and fish meals by worm meal could be could be done between 10 to 15% in broiler diets (Loh et al. 2009). Kocher et al. (2000, 2001) also reported no adverse effect of CM when it was added at 35% of the broilers’ diet. Ahmad et al. (2007) have shown that CM can be used up to 20% of the starter (1–28 days) and finisher (29–42 days) diets without having any adverse effects on broiler performance. The lower metabolisable energy of CM due to high indigestible carbohydrate content and a relatively low true digestibility coefficient of its lysine (NRC 1994) could be resulting in poor growth performance. Min et al. (2009) reported that FI and BW of broilers declined dramatically with the increasing inclusion of CM, with no significant difference in FCR due to canola levels. Woyengo et al. (2010) showed that the expeller-extracted CM had greater apparent metabolisable energy corrected for nitrogen (AME_n) contents than solvent-extracted CM. Saki et al. (2009) showed that extracted soybean meal, as compared to mechanical soybean meal, improved broiler performance.

Table 2.  Body weight (g) of broilers fed experimental diets.

	Body weight (g)
Days of age	0	21	42	49
Treatments
Diets
	40.44	661.78^a	2114.88^a	2694.36^a
SBM^1
CM^2	40.28	621.21^b	1885.21^b	2451.96^b
Enzyme
No enzyme	40.33	633.08^b	1946.96^b	2510.84^b
β-mannanase^3	40.39	649.91^a	2053.12^a	2635.48^a
SEM^4	0.164	4.637	29.732	32.788
	P values
Diet	0.625	<0.01	<0.01	<0.01
Enzyme	0.870	<0.01	0.019	0.015
Diet×Enzyme	0.417	<0.01	0.759	0.488
^1SBM: Corn-soybean meal-based diet
^2CM: Corn-soybean- and canola-meal-based diet
^3Hemicell^®, a β-mannanase-based enzyme commercial product
^4SEM: Standard error of means
^a,bMeans within a column (within main effects) with no common superscript differ significantly (P <0.05).

Dietary partial replacement of SBM by CM decreased (P=0.042) and increased (P<0.01) FI of broilers during the starting and finishing periods, respectively. This observation as well as the lack of significant difference in body weight gain (bwg) during finishing period may be partly due to bird adaptation to CM as they mature. Thacker and Petri (2009) reported that BWG and FI did not differ between birds fed canola biodiesel press cakes and CM; however, FCR was significantly improved for birds fed canola biodiesel press cakes compared with CM.

Table 3. Feed intake (g/chick/day) of broilers fed experimental diets.

	Feed intake (g/chick/day)
Days of age	0–21 (starter)	22–42 (grower)	43–49 (finisher)	0–49 (whole period)
Treatments
Diets
	49.18^a	141.65	185.70^b	107.77
SBM^1
CM^2	48.14^b	137.76	204.35^a	106.24
Enzyme
No enzyme	48.42	139.82	194.72	106.41
β-mannanase^3	48.88	139.59	195.32	107.60
SEM^4	0.253	1.350	3.345	0.728
	P values
Diet	0.042	0.166	<0.01	0.308
Enzyme	0.350	0.933	0.922	0.430
Diet×Enzyme	0.858	0.871	0.488	0.664
^1SBM: Corn-soybean meal-based diet
^2CM: Corn-soybean- and canola-meal-based diet
^3Hemicell^®, a β-mannanase-based enzyme commercial product
^4SEM: Standard error of means
^a,bMeans within a column (within main effects) with no common superscript differ significantly (P <0.05).

Broilers fed the corn-SBM diet had a better FCR compared to those fed the corn-SBM-CM diet during all rearing periods (P<0.05). Biochemical structure of β-mannan in soy and in guar gum is almost identical which provides a potential means of elevating β-mannan in practical diets.

Table 4. Feed conversion ratio (g feed:g gain) of broilers fed experimental diets.

	Feed conversion ratio (g feed:g gain)
Days of age	0–21 (starter)	22–42 (grower)	43–49 (finisher)	0–49 (whole period)
Treatments
Diets
	1.67^b	2.05^b	2.23^b	1.98^b
SBM^1
CM^2	1.76^a	2.35^a	2.74^a	2.23^a
Enzyme
No enzyme	1.73	2.28^a	2.52	2.16^a
β-mannanase^3	1.70	2.12^b	2.44	2.05^b
SEM^4	0.013	0.042	0.112	0.026
	P values
Diet	<0.01	<0.01	0.024	<0.01
Enzyme	0.115	0.019	0.695	<0.01
Diet×Enzyme	0.873	0.603	0.615	0.861
^1SBM: Corn-soybean meal-based diet
^2CM: Corn-soybean- and canola-meal-based diet
^3Hemicell^®, a β-mannanase-based enzyme commercial product
^4SEM: Standard error of means
^a,bMeans within a column (within main effects) with no common superscript differ significantly (P <0.05).

Dietary enzyme supplementation improved BW of birds at 21, 42 and 49 days of age (P<0.05). The same trend was observed in terms of BWG for all periods (P<0.01). Although birds fed enzyme-supplemented diets tended to show higher BWG compared to those fed diets with no added enzyme during the finishing period, the difference was not statistically significant. There was a significant interaction between diet and enzyme on BW of broilers on day 21 of age. Enzyme supplementation was more efficiently increased BW of broilers fed corn-SBM diet than those fed corn-SBM-CM diet (P<0.01). The result of this present study shows that dietary β-mannanase supplementation was more effective in ameliorating the anti-nutritive NSP of the corn-SBM diet than the corn-SBM-CM diet. This result could be partly due to the content of β-mannans in the corn-SBM corn-SBM-CM diets. By using a multi-carbohydrase (xylanase, glucanase, pectinase, cellulase, mannanase and galactanase) Meng and Slominski (2005) reported that the enzyme only improved performance of broiler fed the corn-based diet and enzyme had no significant effect on birds fed the corn-SBM- or the corn-SBM-CM-based diets.

In this study, FI of birds was not affected by enzyme supplementation (P>0.05). Dietary β-mannanase supplementation improved FCR of birds during growing (P=0.019) as well as the overall period (P<0.01). Dietary inclusion of exogenous enzyme blends containing various combinations of amylases, proteases, xylanases, glucanase, cellulase, mannanase and pectinase to corn-soy improved bird performance (Yu and Chung 2004; Cowieson and Adeola 2005). However, dietary supplementation by enzyme containing multi-carbohydrase activities did not improve in growth performance of birds fed SBM-based diets (Kocher et al. 2002). However, no significant improvement in growth performance was seen when similar enzyme products were added to broiler diets with high levels of CM (Kocher et al. 2001). Meng et al. (2005) reported that a multi-carbohydrase containing several enzyme activities is effective in depolymerising cell wall polysaccharides of SBM and CM in vitro. Although dietary enzyme supplementation appeared to be beneficial in enhancing NSP, protein and energy utilisation from corn-SBM diets (Douglas et al. 2000), such effects failed to bring about better growth performance of poultry. This inconsistency in research results using enzyme supplemented corn-SBM- or corn-SBM-CM-based diets may be in part due to dietary level of SBM and CM, variety of oilseed, method of oil extraction and processing of oilseeds, type and level of supplementing enzyme.

Relative weight (g/100g live body weight) of some viscera organs (gizzard, fat pad, liver and pancreas) are presented in (Table 5). There was no interaction between diet and enzyme on relative weight of gizzard, fat pad, liver and pancreas (P>0.05). Dietary inclusion of CM increased the relative weights of gizzard, liver, pancreas (P<0.01) and fat pad (P=0.038). The relative weights of gizzard, fat pad, liver and pancreas were not affected of dietary enzyme supplementation (P>0.05). Ahmad et al. (2007) also reported that the gizzard weight increased linearly with the CM of the diet. The probable reason for increased relative gizzard weight may be partly due to the high fiber and NSP of CM (Kocher et al. 2000), as well as the increased bulkiness (physical form) of diet.

Table 5.  The relative weights (g/100 g live body weight) of gizzard, fat pad, liver and pancreas of broilers fed experimental diets.

	The relative weights (g/100g live body weight)
	Gizzard	Fat pad	Liver	Pancreas
Treatments
Diets
	1.47^b	1.74^b	1.71^b	0.16^b
SBM^1
CM^2	1.79^a	2.01^a	2.25^a	0.19^a
Enzyme
No enzyme	1.68	1.91	2.01	0.18
β-mannanase^3	1.57	1.84	1.95	0.17
SEM^4	0.052	0.065	0.063	0.006
	P values
Diet	<0.01	0.038	<0.01	<0.01
Enzyme	0.273	0.560	0.505	0.306
Diet×Enzyme	0.690	0.478	0.802	0.252
^1SBM: Corn-soybean meal-based diet
^2CM: Corn-soybean- and canola-meal-based diet
^3Hemicell^®, a β-mannanase-based enzyme commercial product
^4SEM: Standard error of means
^a,bMeans within a column (within main effects) with no common superscript differ significantly (P <0.05).

Relative weight (g/100g live body weight) and length (cm/100g live body weight) of digestive tracts (duodenum, jejunum, ileum and caeca) are presented in Table 6 and 7, respectively. There was no interaction between diet and enzyme on relative weight and length of digestive tracts (P>0.05). Dietary inclusion of CM increased the relative weights of duodenum (P=0.035), jejunum (P<0.01) and ileum (P=0.02). The relative weight of ceca was not affected by dietary CM inclusion (P>0.05).

Table 6.  Weight of digestive tracts (g/100 g live body weight) of broilers fed experimental diets.

	Weight of digestive tracts (g/100 g live body weight)
	Duodenum	Jejunum	Ileum	Ceca
Treatments
Diets
	0.39^b	0.84^b	0.86^b	0.32
SBM^1
CM^2	0.46^a	1.05^a	1.02^a	0.36
Enzyme
No enzyme	0.448	0.98	0.98	0.36
β-mannanase^3	0.42	0.91	0.91	0.32
SEM^4	0.016	0.030	0.035	0.013
	P values
Diet	0.035	<0.01	0.020	0.157
Enzyme	0.453	0.188	0.340	0.115
Diet×Enzyme	0.884	0.888	0.566	0.772
^1SBM: Corn-soybean meal-based diet
^2CM: Corn-soybean- and canola-meal-based diet
^3Hemicell^®, a β-mannanase-based enzyme commercial product
^4SEM: Standard error of means
^a,bMeans within a column (within main effects) with no common superscript differ significantly (P <0.05).

Enzyme supplementation did not have significant effect on the relative weight and length of digestive tracts. The NSP’ can cause an increase in intestinal weight through an increased rate of cell-proliferation, leading to changes in mucosal structure and function.

Table 7. Length of digestive tracts (cm/100g live body weight) of broilers fed experimental diets.

	Length of digestive tracts (cm/100g live body weight)
	Duodenum	Jejunum	Ileum	Ceca
Treatments
Diets
	1.02^b	2.37^b	2.68^b	0.67^b
SBM^1
CM^2	1.23^a	3.10^a	3.29^a	0.80^a
Enzyme
No enzyme	1.12	2.82	3.07	0.77
β-mannanase^3	1.13	2.66	2.90	0.71
SEM^4	0.029	0.093	0.099	0.026
	P values
Diet	<0.01	<0.01	<0.01	<0.01
Enzyme	0.856	0.275	0.312	0.183
Diet×Enzyme	0.860	0.325	0.165	0.982
^1SBM: Corn-soybean meal-based diet
^2CM: Corn-soybean- and canola-meal-based diet
^3Hemicell^®, a β-mannanase-based enzyme commercial product
^4SEM: Standard error of means
^a,bMeans within a column (within main effects) with no common superscript differ significantly (P <0.05).

The results of litter moisture and pH are presented in Table 8. There was no interaction between diet and enzyme on litter moisture and pH (P>0.05). Dietary CM inclusion and enzyme supplementation did not significantly affect litter moisture and pH, except for the litter pH on week 7 which was higher in the corn-SBM dietary group than the corn-SBM-CM group (P=0.031). Litter moisture is an important litter quality parameter. Litter which is not kept at an appropriate level, very high bacterial loads and unsanitary growing conditions may produce ammonia and other gases which in turn cause odors, insect problems, soiled feathers, footpad lesions and breast bruises or blisters. Although Daskiran and Teeter (2004)) reported that dietary enzyme partially degraded β-mannan and reduced water consumption and excretion by birds, this effect was not observed in the present study. It may be partly due to the level of SBM replacement by CM or the level of enzyme used. In conclusion, broilers fed a diet containing 15% CM did not achieve equivalent growth performance compared to birds fed corn-SBM diet. Dietary β-mannanase supplementation improved performance of broilers fed corn-SBM- and/or corn-SBM-CM-based diets.

Table 8.  Litter parameters of broilers fed experimental diets.

	Litter parameters
	Moisture week 3	Moisture week 5	Moisture week 7	pH week 5	pH week 7
Treatments
Diets
	22.35	28.22	38.02	7.22	8.12^a
SBM^1
CM^2	22.73	29.47	39.15	6.87	7.60^b
Enzyme
No enzyme	22.62	28.91	38.85	7.15	7.86
β-mannanase^3	22.47	28.78	38.32	6.94	7.85
SEM^4	1.097	1.713	2.339	0.176	0.121
	P values
Diet	0.868	0.730	0.819	0.348	0.031
Enzyme	0.948	0.973	0.915	0.551	0.972
Diet×Enzyme	0.987	0.939	0.967	0.635	0.148
^1SBM: Corn-soybean meal-based diet
^2CM: Corn-soybean- and canola-meal-based diet
^3Hemicell^®, a β-mannanase-based enzyme commercial product
^4SEM: Standard error of means
^5Means±SD
^a,bMeans within a column (within main effects) with no common superscript differ significantly (P <0.05).

Acknowledgements

Appreciation is expressed to Research Sector of Razi University, Kermanshah, Iran, for financial and material support of this research. The authors are also grateful to Dr. B.A. Slominski, Department of Animal Science, University of Manitoba and Dr. W.E. Huff, United States Department of Agriculture; Poultry Research Laboratory, University of Delaware, for their kind and scientific guidance for the present study.