Interactions of dietary wheat cultivars and NSP-degrading enzyme on productive performance and egg quality traits

Abstract

Context

The nutritional value of enzyme-supplemented wheat-contained diets can be influenced by interactions between wheat cultivar and exogenous enzyme, which in turn cause various effects on the performance of poultry.

Aims

The effects of diets including various wheat cultivars with or without enzyme on productive performance and egg quality characteristics were evaluated.

Methods

A total of 270 58-week-old Lohmann LSL-Lite were allocated to 9 experimental dietary groups with 5 replicate cages and 6 birds per each cage. Based on a 4 × 2 factorial arrangement of treatment, nine iso-caloric and iso-nitrogenous experimental diets, including four wheat cultivars (Sardari, Azar 2, Pishgam and Sirvan) with and without enzymes plus a corn-based control diet, were tested in a completely randomized design during an 8-week trial period.

Key results

From weeks 58 to 63 and 63 to 67 of age, the hens fed with Sardari-included diet showed the lowest feed intake compared to other groups (p < 0.05). Egg production (EP), feed conversion ratio (FCR) and egg mass (EM) were not influenced by the experimental diets. At the age of 62 weeks, the effect of adding enzyme on egg shape index was significant. Moreover, in sampling week 67, increased eggshell weight (%) was detected in enzyme-supplemented diets compared to diets with no enzyme (10.03 vs. 9.37, respectively). Besides, the shell thickness was the highest in the group fed with Azar 2, and the lowest in the group fed with Sirvan at the age of 67 weeks (p < 0.05). Albumen weights (%) were also significant in some cases. The highest albumen weight was observed in Sirvan-included diet without enzyme on week 62. Reduced yolk weight was detected in enzyme-supplemented Pishgam-included diet on 62 weeks of age (p < 0.05).

Conclusions

The inclusion of the diets of laying hens with the four tested Iranian wheat cultivars has no negative impact on most productive performance and egg quality indices. Moreover, supplementing the wheat-included diets with non-starch polysaccharidase enzyme (beta-endopower) improved eggshell weight on week 67.

INTRODUCTION

Corn is by far the major feed grain grown worldwide. Although it is the preferred grain for poultry diet, it is found to be low in protein content and quality. In addition, maize has long been an important ingredient in the manufacture of alcoholic beverages and industrial alcohols. This antagonism in maize use has necessitated searches for other cereals to be used in poultry diets instead of corn. Wheat is also used in poultry diets because of its availability; however, its use is limited due to its variable chemical composition and high content of non-starch polysaccharides (NSPs) (Ordaz-Ortiz & Saulnier, 2005). The main constituent of NSPs in the cell wall of wheat, triticale endosperm and rye is pentosan with some β-glucan (Engberg et al., 2004). These compounds reduce the availability of nutrients by increasing the viscosity of the contents in the gastrointestinal tract (Bakhtiyary Moez et al., 2020). The nutritional quality of diets containing wheat can be improved by adding exogenous enzymes (Adeola & Bedford, 2004; Bedford & Morgan, 1996; Pirgozliev et al., 2010). Xylanase is an enzyme that reduces the viscosity of digestive contents by breaking the long chains of wheat arabinoxylans and converting them to short-chain xylo-oligomers, which in turn releases nutrients and increases their digestion in animals (Masey-O'Neill et al., 2014; Zhang et al., 2014). The number of dirty eggs in birds fed with NSPs increased due to the high viscosity of the digestive contents, which, in part, reduced the marketable eggs and increased the economic loss of producers (Olgun et al., 2018). Improvements in feed conversion ratio (FCR), egg mass (EM) and egg production (EP) in laying hens fed with xylanase-supplemented diets have been reported (Bobeck et al., 2014; Senkoylu et al., 2009). The negative impact of adding wheat or NSPs on the performance of laying hens decreased and even disappeared as a result of adding xylanase supplement to the diet (Mirzaie et al., 2012). However, the inclusion of wheat offal at graded level to replace corn with hemi-cell enzyme supplement reduced the feed intake (FI) and digestibility of the nutrients in broiler chickens (Ereke et al., 2017). In contrast, the supplemental xylanase in wheat-based diets had no significant impact on the productive performance of laying hens and egg quality traits except for yolk colour, which was improved (Pirgozliev et al., 2010). In addition, supplementing wheat-contained diets with xylanase had no significant effect on the performance parameters of laying hens (Cufadar et al., 2010; Lei et al., 2018). Although there are many studies in this field, as it is clear from the results of various experiments, the use of different wheat cultivars and enzymes in the diet of birds can have a different impact on the productive performance and egg quality traits, which can be partly caused by the difference in the chemical composition of wheat, and the solubility of exogenous NSPs as well as the type and amount of enzyme (Nguyen et al., 2021). The main hypothesis for conducting this study was that the interactions between wheat cultivar and enzyme can affect bird performance. The purpose of the present study was therefore to include diets of laying hens with four Iranian wheat cultivars and evaluate their interactions with dietary supplemental non-starch polysaccharidase (NSPase) (beta-endopower) on the productive performance of the birds and egg quality traits.

MATERIALS AND METHODS Experimental design and diets

All experimental protocols adhered to the guidelines approved by the Animal Ethics Committee of Razi University, Kermanshah, Iran and were in accordance with the EU standards for the protection of animals and/or feed legislation. In the current study, 270 58-week-old Lohmann LSL-Lite laying hens (mean live weight 1614 g) were used. The birds were randomly allocated to 9 treatments with 5 replicate cages and 6 birds per cage in a completely randomized design (30 hens in each group). Mash feeds (110 g/hen/day) were hand-dispensed every day. The laying hens were placed in the cages under normal temperature (18–20°C) and relative humidity (40%–45%), with 16 h of light and 8 h of a dark cycle for 8 weeks (58–67 weeks of age). A corn–soybean meal-based diet as a control group was fed to laying hens that were adjusted according to hens’ requirements as recommended by the Lohmann LSL-Lite management guide (metabolizable energy [ME] = 2650 kcal/kg and crude protein, CP = 160 g/kg diet). Based on a 4 × 2 factorial arrangement of treatment, nine iso-caloric and iso-nitrogenous experimental diets included four wheat cultivars (Sardari, Azar 2, Pishgam and Sirvan) with or without enzyme, plus a corn-based control diet, were tested in a completely randomized design (Table 1).

TABLE 1 Ingredients and composition of the experimental diets.

		Diets based on different wheat cultivars
Ingredients	Control diet	Sardari	Azar 2	Pishgam	Sirvan
Corn	54.15	–	–	–	–
Wheat: Sardari	–	61.08	–	–	–
Wheat: Azar 2	–	–	61.38	–	–
Wheat: Pishgam	–	–	–	61.21	–
Wheat: Sirvan	–	–	–	–	63.85
Soybean meal	23.24	22.91	22.59	22.77	20.19
Wheat bran	6.66	–	–	–	–
Vegetable oil	2.00	2.00	2.00	2.00	2.00
Calcium carbonate	4.00	4.00	4.00	4.00	4.00
Di-calcium phosphate	1.73	1.72	1.72	1.72	1.72
Oyster shell	6.34	6.26	6.26	6.26	6.24
Salt	0.37	0.33	0.33	0.33	0.33
Vitamin premixa	0.30	0.30	0.30	0.30	0.30
Mineral premixb	0.30	0.30	0.30	0.30	0.30
l-Lysine	0.10	0.30	0.30	0.30	0.30
l-Threonine	0.03	0.03	0.03	0.03	0.03
DL-methionine	0.18	0.17	0.19	0.18	0.18
Sodium bicarbonate	0.10	0.10	0.10	0.10	0.10
Acidifier and toxin binder	0.50	0.50	0.50	0.50	0.50
Calculated analysis
ME (kcal/kg)	2650	2650	2650	2650	2650
Crude protein (%)	16.00	16.00	16.00	16.00	16.00
Ether extract (%)	4.25	3.21	3.38	3.32	3.36
Crude fibre (%)	3.55	2.95	3.23	3.12	2.84
Calcium (%)	4.40	4.40	4.40	4.40	4.40
Available phosphorus (%)	0.45	0.45	0.45	0.45	0.45
Digestible amino acids
Arginine (%)	0.90	0.89	0.87	0.88	0.82
Glycine (%)	0.61	0.59	0.58	0.60	0.57
Serine (%)	0.70	0.71	0.69	0.70	0.70
Histidine (%)	0.38	0.36	0.35	0.35	0.34
Isoleucine (%)	0.58	0.58	0.56	0.57	0.56
Leucine (%)	1.25	1.03	1.00	1.02	1.00
Lysine (%)	0.71	0.87	0.91	0.95	0.86
Methionine (%)	0.40	0.38	0.39	0.38	0.38
Methionine + cystine (%)	0.64	0.64	0.64	0.64	0.64
Phenylalanine (%)	0.68	0.66	0.64	0.65	0.66
Tyrosine (%)	0.57	0.51	0.50	0.51	0.44
Threonine (%)	0.55	0.53	0.52	0.52	0.50
Tryptophan (%)	0.20	0.21	0.21	0.21	0.20
Valine (%)	0.67	0.65	0.64	0.64	0.63

a

Vitamin mixture per 0.3 kg/100 kg of diet: vitamin A, 7700,000 IU; vitamin D3, 3300,000 IU; vitamin E, 6600 mg; vitamin K3, 550 mg; thiamine,2200 mg; riboflavin, 4400 mg; vitamin B6, 4400 mg; capantothenate, 550 mg; nicotinic acid, 200 mg; folic acid, 110 mg; choline chloride, 275,000 mg; biotin,55 mg; vitamin B12, 8.8 mg.

b

Mineral mixture per 0.3 kg/100 kg of diet: Mn, 66,000 mg; Zn, 66,000 mg; Fe, 33,000 mg; Cu, 8800 mg; Se, 300 mg.

Wheat cultivars and enzyme

The four Iranian wheat cultivars (Sardari, Azar 2, Pishgam and Sirvan), used in this experiment, were obtained via wheat distribution companies under the supervision of the Agricultural Research Institute of Kurdistan and Kermanshah Provinces, Iran. The enzyme used in this research study was a multivalent enzyme, beta-endopower, which is a combination of alpha galactosidase, galactomananase, xylanase and beta-glucanase (200 g/t were used for all enzyme-supplemented wheat diets) produced from solid-state fermentation of non-GMO fungi, Aspergillus niger and Aspergillus oryzae.

Chemical analysis

Before the experiment, wheat cultivars were analysed to determine the chemical composition (Table 2), and the experimental diets were formulated accordingly. Based on the methods of Horowitz and Latimer (2006), dry matter, crude protein, crude fibre, crude fat, ash, sugar and starch content were determined. In addition, neutral detergent fibre and acid detergent fibre (ADF) were measured by the methods of Van Soest et al. (1991). Based on the methods 32-07.01 and 991.43 of AACC (American Association of Cereal Chemists), the Megazyme assay kits (K-TDFR) were used to measure NSPs and soluble and insoluble fibres. Moreover, the content of amylose and amylopectin was determined by the specific Megazyme kit (K-AMYL). A calorimeter bomb (Parr 1261), standardized with benzoic acid, was used to measure the gross energy. To measure calcium and phosphorus, the wheat samples were first ashed, digested according to the method described by Horowitz and Latimer (2006) and then read by a spectrophotometer (Jenway Model 6300).

TABLE 2 Chemical analysed composition of the different wheat cultivars.

Chemical composition (% DM)	Wheat cultivars
Parameters	Sardari	Azar 2	Pishgam	Sirvan
Dry matter	94.18	94.34	96.61	96.61
Crude protein	9.58	9.05	9.20	11.98
Crude fibre	3.00	2.80	2.40	3.16
NFE	78.66	78.83	76.09	72.79
NDF	12.75	13.50	11.25	15.75
ADF	2.75	2.50	2.25	3.50
ADL	8.75	9.90	8.30	11.4
Ash	1.50	1.40	1.55	2.65
Crude fat	1.30	2.00	2.50	1.90
Gross energy (kcal/kg)	4125	4128	4082	4003
AMEn (kcla/kg)a	3109	3095	3101	3102
Calcium	0.42	0.30	0.18	0.28
Phosphor	0.25	0.22	0.15	0.12
Sugar	5.31	6.06	5.17	5.58
Starch	74.95	68.73	75.88	56.75
Insoluble fibre	18.367	12.483	16.622	19.712
Soluble fibre	4.110	4.568	6.077	8.292
NSPsb	11.75	12.70	10.70	15.4
Amylose (%)	7.29	4.80	6.61	6.69
Amylopectin (%)	92.71	95.20	93.39	93.31

Abbreviations: ADF, acid detergent fibre; ADL, acid detergent lignin; DM, dry matter; NDF, neutral detergent fibre; NFE, nitrogen-free extract.

a

Apparent metabolizable energy (standardized to a dry matter content of 88%) – Evonik Nutrition & Care GmbH/Analytical Report AMINONRG, www.aminonrg.com.

b

NSPs, non-starch polysaccharides; cellulose = NDF − ADF, cellulose = ADF − (ADL + Ash), NSP = crude fibre + ADL (Kalantar & Yaghobfar, 2016).

Performance parameters

After 1-week adaptation period, data collection from the experimental groups was started. Feed residual was weighted weekly, and then, FI was measured on a cage basis. Every day the numbers of eggs laid by each replicate were collected and eggs weighed (EW), using an electronic weighing scale, and the average was recorded. At the end of each month (62 and 67 weeks), FCR, EP and EM were calculated.

Egg quality traits

At weeks 62 and 67 of age, 2 eggs per replicate cage were randomly sampled for 3 days (30 eggs per treatment), and egg quality indices, including egg index, yolk index, the Haugh unit, shell weight, shell thickness, yolk colour, egg gravity, albumen and yolk weight, were measured. At first, the length and width of the eggs were measured by a compass, and the egg shape index was calculated by the formula (width/length) × 100. Then, egg-specific gravity was estimated using six normal salt solutions with gradual increasing concentrations, which presented specific gravity of 1000, 1062, 1070, 1082, 1090 and 1102 (Hempe et al., 1988). The Haugh unit formula was used to calculate the Haugh index, which is based on the egg weight and the albumen height, measured by a micrometre (Eisen et al., 1962). The yolk index was assessed as a ratio of the yolk height by the yolk diameter using a compass (WELLS, 1968). To measure the thickness of the shell, an average of three different parts of the shell was used, which were measured by a dial and pipe gauge. Moreover, the yolk colour was measured using the DSM fan scale. The eggshell percentage was determined using the individual weight of each egg and the shell weight.

Statistical analysis

The obtained data from a 4 × 2 factorial arrangement of treatments were analysed based on a completely randomized design using SAS software version 9.4 (SAS Institute, 2015). In factorial arrangement, the model was Y_ijk = μ + A_i + B_j + AB_ij + e_ijk, where Y_ijk is the measured characteristic, μ is the overall mean, (A_i) is the effect of wheat cultivar, (B_j) is the effect of the enzyme, (AB_ij) is the interaction between wheat cultivar and enzyme and (e_ijk) is the residual error. The least significant difference test was used to compare the mean values. Each time the interaction was significant, the effects of the main factors were ignored. The following model was used to compare the mean of nine experimental treatments by a completely randomized design, Y_ij = μ + T_i + e_i, where Y_ijk is the measured characteristic, μ is the overall mean, (T_i) is experimental treatments and (e_i) is the residual error.

RESULTS Productive performance

The effects of diets containing different wheat cultivars with or without enzyme on the productive performance of laying hens are shown in Tables 3 and 4. The effects of dietary treatments on EP, EM and FCR during the periods of 58–62, 63–67 and 58–67 weeks of age were not significant (p > 0.05). In a comparison of nine dietary treatments, EW was reduced in diets containing different wheat cultivars compared to the corn-based control diet within 63–67 weeks. Significant effects of dietary treatments on FI from 63 to 67 and 58 to 67 weeks of age were detected (p < 0.05). In these periods, the dietary groups with Sardari wheat cultivar had the lowest FI compared to the other cultivars (p < 0.05). Moreover, in comparing nine experimental dietary treatments, the Sardari-included diet with and without enzyme and corn-based diet had the lowest FI compared to other dietary groups (p < 0.05) (Table 4). The interactions between dietary wheat cultivar and enzyme for BWG were significant (p < 0.05). Besides, the reduced BWG of layers fed with enzyme-supplemented diets compared to diets with no enzyme was observed (p < 0.05). The highest BWG was related to hens fed with Azar 2–included diet with no supplemental enzyme (p < 0.05). In comparing nine experimental dietary treatments, the lowest BWG was observed in Sirvan- and Azar 2–included diets with enzyme and corn-based diet (Table 4).

TABLE 3 Effects of replacing dietary corn with four different Iranian wheat cultivars with or without enzyme on the productive performance of laying hens.

	Egg weight (g)			Egg production (%)			Egg mass (g/hen/day)
Weeks of age	58–62	63–67	58–67	58–62	63–67	58–67	58–62	63–67	58–67
Wheat cultivar (WC)
Sardari	61.25	62.25	61.74	91.87	89.01	90.44	57.44	56.54	56.99
Azar 2	60.62	62.33	61.46	86.62	85.16	85.89	53.68	54.22	53.95
Pishgam	60.96	62.63	61.80	88.37	87.38	87.88	55.05	55.93	55.49
Sirvan	60.86	62.21	61.54	87.85	88.90	88.37	54.55	56.43	55.49
p-Value	0.860	0.790	0.924	0.434	0.655	0.590	0.450	0.755	0.646
SEM	0.514	0.327	0.401	2.323	2.432	2.324	1.690	1.704	1.661
Enzyme
Zero	60.90	62.35	61.62	88.22	86.47	87.35	54.87	55.04	54.96
0.2 (g/kg)	60.94	62.36	61.65	89.13	88.75	88.94	55.49	56.52	56.00
p-Value	0.937	0.986	0.927	0.700	0.356	0.498	0.720	0.394	0.534
SEM	0.364	0.231	0.284	1.644	1.717	1.642	1.196	1.209	1.174
WC × E
p-Value	0.806	0.889	0.941	0.768	0.974	0.935	0.860	0.975	0.977
CV	2.69	2.64	2.12	7.84	8.42	7.89	9.22	9.32	9.03
Treatment
WC E
Sardari−	61.08	62.46ab	61.76	89.60	88.08	88.84	55.92	56.16	56.04
Sardari+	61.41	62.04b	61.72	94.15	89.95	92.05	58.97	56.92	57.95
Azar 2−	60.93	62.29ab	61.59	85.86	83.06	84.46	53.44	52.82	53.13
Azar 2+	60.32	62.36ab	61.33	87.38	87.26	87.32	53.92	55.62	54.77
Pishgam−	60.61	62.59ab	61.58	89.48	86.68	88.08	55.40	55.41	55.40
Pishgam+	61.32	62.68ab	62.01	87.26	88.08	87.68	54.70	56.45	55.58
Sirvan−	61.00	62.07b	61.53	87.96	88.08	88.02	54.74	55.79	55.26
Sirvan+	60.73	62.35ab	61.55	87.73	89.71	88.72	54.36	57.08	55.72
Corn	60.67	64.32a	62.44	89.83	88.08	88.95	55.62	57.76	56.69
p-Value	0.983	0.052	0.957	0.781	0.929	0.913	0.846	0.931	0.943
SEM	0.734	0.738	0.586	3.112	3.303	3.110	2.271	2.332	2.244

Note: Means with different superscripts in columns differ significantly (p ≤ 0.05). Values are expressed as mean.

Abbreviations: CV, coefficient of variation; SEM, standard error of the mean.

TABLE 4 Effects of replacing dietary corn with four different Iranian wheat cultivars with or without enzyme on the performance of laying hens.

	Feed intake (g/hen/day)			Feed conversion ratio (g/g)		Body weight gain (g)
Weeks of age	58–62	63–67	58–67	58–62	63–67	58–67	58–67wk
Wheat cultivar (WC)
Sardari	109.65	109.71b	109.86b	1.91	1.95	1.93	306.40
Azar 2	109.66	109.85a	109.92a	2.06	2.05	2.06	341.00
Pishgam	109.58	109.85a	109.92a	2.01	1.98	2.00	283.20
Sirvan	109.60	109.94a	109.97a	2.01	1.95	1.99	266.00
p-Value	0.430	0.030	0.050	0.477	0.708	0.624	0.777
SEM	0.038	0.032	0.016	0.068	0.067	0.066	65.96
Enzyme
Zero	109.64	109.82	109.91	2.01	2.00	2.01	388.00a
0.2 (g/kg)	109.61	109.85	109.93	1.99	1.96	1.98	220.30b
p-Value	0.436	0.319	0.347	0.772	0.497	0.613	0.007
SEM	0.026	0.023	0.011	0.048	0.047	0.047	46.643
WC × E
p-Value	0.625	0.207	0.220	0.861	0.976	0.965	0.049
CV	0.11	0.10	0.05	10.26	10.29	10.07	73.11
Treatment
WC E
Sardari−	109.62	109.69c	109.85c	1.97	1.96	1.97	375.80ab
Sardari+	109.67	109.73c	109.87c	1.86	1.93	1.90	237.00b
Azar 2−	109.70	109.79bc	109.90bc	2.07	2.09	2.09	418.00a
Azar 2+	109.62	109.90ab	109.95ab	2.06	2.00	2.03	184.00b
Pishgam−	109.62	109.89ab	109.95ab	1.99	1.99	1.99	320.20ab
Pishgam+	109.55	109.81bc	109.90bc	2.03	1.98	2.01	246.20b
Sirvan−	109.61	109.91ab	109.95ab	2.01	1.98	2.00	338.00ab
Sirvan+	109.59	109.97a	109.98a	2.02	1.93	1.98	174.00b
Corn	109.70	109.74c	109.87c	1.97	1.90	1.94	192.00b
p-Value	0.670	0.031	0.032	0.860	0.933	0.933	0.044
SEM	0.058	0.050	0.024	0.091	0.091	0.089	92.101

Note: Means with different superscripts in columns differ significantly (p ≤ 0.05). Values are expressed as mean.

Abbreviations: CV, coefficient of variation; SEM, standard error of the mean.

Egg quality traits

The effects of dietary wheat cultivar and enzyme on the egg quality traits of laying hens are presented in Tables 5–7. No significant effects of dietary treatments were observed on the yolk index and egg-specific gravity. There was a significant effect of dietary treatments on the Haugh unit between some wheat cultivars on week 67. In the first egg sampling at 62 weeks of age, the higher egg shape index was detected in laying hens fed with the enzyme-supplemented diets (p < 0.05) (Table 5). In comparing nine experimental dietary treatments, the highest egg shape index was observed in Azar 2–included diet with enzyme, and the lowest egg shape index was observed in Sirvan-included diet with no enzyme (p < 0.05). Besides, in the second egg sampling at week 67, the highest egg shape index was observed in the corn and Sardari with enzyme-included diet, which had a significant difference with the diet containing Sirvan without enzyme. Concerning the shell thickness, the highest was observed in the group fed with Azar 2, and the lowest in the group fed with Sirvan at the age of 67 weeks (p < 0.05).

TABLE 5 Effects of replacing dietary corn with four different Iranian wheat cultivars with or without enzyme on egg quality traits of laying hens at 62 and 67 weeks of age.

	Haugh unit1		Egg shape index (%)2		Yolk index (%)3
Age (week)	62	67	62	67	62	67
Wheat cultivar (WC)
Sardari	79.48	79.96	75.07ab	75.79	35.08	35.07
Azar 2	79.56	82.82	75.82a	74.98	34.97	35.67
Pishgam	81.65	80.73	74.27ab	75.25	35.53	35.57
Sirvan	80.30	79.65	73.37b	74.40	35.44	36.10
p-Value	0.673	0.374	0.023	0.725	0.960	0.853
SEM	1.34	1.37	0.847	0.871	0.868	0.822
Enzyme
Zero	80.42	79.57	73.67b	74.22	34.46	35.66
0.2 (g/kg)	79.64	82.00	75.59a	75.99	35.04	35.54
p-Value	0.383	0.087	0.030	0.501	0.631	0.890
SEM	0.947	0.975	0.599	0.615	0.614	0.581
WC × E
p-Value	0.349	0.473	0.133	0.793	0.760	0.474
CV	5.49	5.99	3.80	3.53	7.83	7.22
Treatment
WC E
Sardari−	78.34	76.83b	75.46ab	75.16ab	35.79	35.85
Sardari+	80.63	83.08a	74.68abc	76.43a	34.37	34.30
Azar 2−	81.35	82.17ab	73.77bc	74.17ab	34.49	36.31
Azar 2+	77.77	83.47a	77.87a	75.78ab	35.44	35.02
Pishgam−	81.85	80.15ab	73.97bc	74.76ab	35.57	35.07
Pishgam+	81.58	81.31ab	74.57abc	75.73ab	35.50	36.07
Sirvan−	82.04	79.15ab	71.48c	72.78b	36.01	35.40
Sirvan+	78.57	80.15ab	75.26ab	76.03ab	34.86	36.79
Corn	80.37	78.29ab	75.39ab	76.46a	36.13	34.54
p-Value	0.718	0.054	0.057	0.042	0.973	0.826
SEM	1.97	2.15	1.27	1.18	1.23	1.14

Note: Means with different superscripts in columns differ significantly (p ≤ 0.05). Values are expressed as mean.

Abbreviations: CV, coefficient of variation; SEM, standard error of the mean.

1

Haugh unit, h is the observed height of the albumen in millimetre, w is the weight of egg in grams, HU = 100 × log₁₀ (h − 1.7w^0.37 + 7.6).

2

The ratio of width to length of the egg.

3

The ratio of yolk height over yolk diameter ×100.

In the second egg sampling at 67 weeks of age, increased shell weight was observed in the birds fed with enzyme-supplemented diets (p < 0.05) (Table 6). In comparing nine experimental dietary treatments, the highest shell weight was observed in laying hens fed with Azar 2–included diet with enzyme, and the lowest shell weight was observed in Pishgam- and Azar 2–included diet with no enzyme (p < 0.05) (Table 6). The interactions between dietary wheat cultivar and enzyme for yolk and albumen weight were significant (p < 0.05) (Table 7). Concerning albumen weight on week 62, the differences between Sirvan-included diets with and without enzyme were significant, so that enzyme reduced albumen weight (p < 0.05). The highest albumen weight was observed in Sirvan-included diet without enzyme, and the lowest albumen weight was related to the enzyme-supplemented Azar 2–included diet (Table 7). The highest yolk weight was related to the corn-based diet, and the lowest was observed in the enzyme-supplemented Azar 2–included diet on week 62 (p < 0.05). Reduced yolk weight was detected in enzyme-supplemented Pishgam-included diet compared to the Pishgam diet without enzyme (p < 0.05) (Table 7). In both egg samplings (62 and 67 weeks of age), effects of dietary treatments on yolk colour were significant (p < 0.05) (Table 7). The laying hens fed with corn-based diet diets showed improved yolk colour scores compared to those fed with the wheat-contained diets (p < 0.05).

TABLE 6 Effects of replacing dietary corn with four different Iranian wheat cultivars with or without enzyme on egg quality traits of laying hens at 62 and 67 weeks of age.

	Eggshell weight (%)		Eggshell thickness (10−2 mm)		Egg-specific gravity
Age (week)	62	67	62	67	67
Wheat cultivar (WC)
Sardari	9.86	9.65	41.56	42.06ab	1.08
Azar 2	10.02	9.91	42.92	44.86a	1.08
Pishgam	10.02	9.38	41.73	41.13ab	1.08
Sirvan	9.89	9.82	38.93	38.72b	1.08
p-value	0.946	0.236	0.390	0.053	0.573
SEM	0.238	0.190	1.651	1.852	0.001
Enzyme
Zero	9.98	9.37b	40.93	40.16	1.08
0.2 (g/kg)	9.92	10.03a	41.64	43.23	1.08
p-Value	0.798	0.001	0.668	0.107	0.825
SEM	0.168	0.134	1.172	1.303	0.001
WC × E
p-Value	0.892	0.234	0.956	0.278	0.930
CV	7.90	6.37	12.00	13.39	0.54
Treatments
WC E
Sardari−	9.93	9.49bc	41.53	40.66b	1.08
Sardari+	9.79	9.82abc	41.59	43.46ab	1.08
Azar 2−	9.92	9.23c	41.86	40.33b	1.08
Azar 2+	10.13	10.58a	43.99	49.39a	1.08
Pishgam−	10.17	9.17c	41.26	41.59b	1.08
Pishgam+	9.87	9.59bc	42.19	40.66b	1.08
Sirvan−	9.90	9.49bc	39.06	38.06b	1.08
Sirvan+	9.88	10.15ab	38.79	39.39	1.08
Corn	10.38	10.29ab	43.73	42.46ab	1.09
p-Value	0.967	0.019	0.746	0.046	0.741
SEM	0.353	0.277	2.23	2.50	0.002

Note: Values are expressed as mean. Means with different superscripts in columns differ significantly (p ≤ 0.05).

Abbreviations: CV, coefficient of variation; SEM, standard error of the mean.

TABLE 7 Effects of replacing dietary corn with four different Iranian wheat cultivars with or without enzyme on egg quality traits of laying hens at 62 and 67 weeks of age.

	Albumen weight (%)		Yolk weight (%)		Yolk colour
Age (week)	62	67	62	67	62	67
Wheat cultivar (WC)
Sardari	53.76	56.92	30.60a	30.35	1.00	1.00b
Azar 2	53.96	56.13	28.33b	30.10	1.00	1.20a
Pishgam	56.92	54.78	31.17a	29.86	1.00	1.00b
Sirvan	57.00	54.94	30.71a	28.98	1.10	1.00b
p-Value	0.142	0.600	0.026	0.411	0.405	0.054
SEM	1.288	1.280	0.678	0.600	0.050	0.061
Enzyme
Zero	57.13a	55.06	30.86	29.31	1.00	1.00
0.2 (g/kg)	53.69b	56.32	29.54	30.32	1.05	1.10
p-Value	0.011	0.333	0.059	0.102	0.324	0.112
SEM	0.910	0.905	0.479	0.424	0.035	0.043
WC × E
p-Value	0.030	0.520	0.034	0.531	0.405	0.064
CV	7.36	7.09	8.99	10.91	34.11	29.13
Treatment
WC E
Sardari−	52.12c	56.94	30.21bcd	30.07ab	1.00b	1.00b
Sardari+	55.41bc	56.89	30.99abc	30.63ab	1.00b	1.00b
Azar 2−	56.33abc	56.12	29.28cd	30.02ab	1.00b	1.00b
Azar 2+	51.58c	56.15	27.38d	30.18ab	1.00b	1.40b
Pishgam−	59.22ab	54.55	33.44ab	29.46ab	1.00b	1.00b
Pishgam+	54.63bc	55.01	28.89cd	30.26ab	1.00b	1.00b
Sirvan−	60.87a	52.63	30.52bcd	27.72b	1.00b	1.00b
Sirvan+	53.13c	57.24	30.89abcd	30.24ab	1.10b	1.00b
Corn	56.21abc	56.20	34.12a	32.23a	2.20a	2.40a
p-Value	0.013	0.701	0.012	0.743	0.003	0.001
SEM	1.82	1.76	1.23	1.46	0.176	0.156

Note: Means with different superscripts in columns differ significantly (p ≤ 0.05). Values are expressed as mean.

Abbreviations: CV, coefficient of variation; SEM, standard error of the mean.

DISCUSSION Growth performance

In this study, four different varieties of wheat, including Sardari, Sirvan, Pishgam and Azar 2, showed differences in terms of chemical compositions (Table 2). The variation in energy and nutrient content among different wheat cultivars has been reported previously (Nguyen et al., 2021). According to our result, the content of crude protein was highest in Sirvan (11.98%) and lowest in Azar 2 (9.05%), whereas the content of crude fat was highest in Pishgam (2.50%) and lowest in Sardari wheat cultivars (1.30%). Moreover, among different wheat cultivars, the concentration of gross energy, insoluble and soluble fibres, NSPs and starch ranged from 4003 to 4128 kcal/kg, 12.48% to 19.71%, 4.11% to 8.29% and 10.70% to 15.40%, 56.75% to 75.88%, respectively (DM basis).

In the current study, including diets with wheat cultivars with or without enzymes did not affect the EP, EM and FCR in laying hens, whereas some treatments showed a slight decrease in EW compared to the control treatment. These results show that the dietary treatments met the nutritional requirement of laying hens, and that the variations of NSPs across various wheat cultivars had no significant effect on the aforementioned performance parameters. Cufadar et al. (2010), who added three levels of xylanase to five different ratios of corn and wheat in the layers’ diet, also showed no significant impact of various treatments on EP, EW and FCR. In addition, Lei et al. (2018) reported no significant effect of increasing xylanase supplemental levels in the wheat and corn–soybean meal-based diets on EW, EP, EM and FCR in laying hens; however, the interaction between soluble NSPs levels and xylanase on EP was significant. Decreased EP in laying hens fed diets with high levels of NSPs with supplemental enzyme was reported during 25–28 weeks of age (Nguyen et al., 2021). Rafuse et al. (2004) examined the effect of four Canadian wheat varieties with or without enzyme on the performance of laying hens and reported no significant effect of the experimental diets on EP, FCR and EW. In contrast, a significant decrease in EW and EM with no significant effect on EP were observed in the research study with increasing levels of dietary wheat (Mirzaie et al., 2012), but supplementing diets with xylanase improved EM, EP and FCR. The variations between the results of different experiments could be partly attributed to differences in level and cultivar of the evaluated wheat cultivar or variety, type and level of the supplemental enzyme and the age of laying hens.

In the present experiment, laying hens fed with the diets, including Azar 2, Sirvan and Pishgam wheat cultivars, had higher FI compared to those fed with Sardari-included and corn-based diets. The apparent ME (AME) of the four evaluated wheat cultivars was calculated using energy estimation equations, and then, the experimental diets were formulated as iso-caloric and iso-nitrogenous (ME = 2650 kcal/kg and CP = 160 g/kg diet). It seems that the AME of wheat cultivars except for Sardari was probably overestimated, and eventually, layers increased their FI as an adaptation mechanism to low-energy diets (Grobas et al., 1999). In the study of Hadorn et al. (1996), FI was not significantly affected by enzyme addition in laying hens fed with wheat-based diet. Rafuse et al. (2004), who evaluated the effects of supplemental enzymes on the performance of laying hens fed with diets contained four wheat cultivars, found that FI was significantly affected by the bird age, so that the highest and the lowest FI were observed in the first and third weeks of trial. In a study, the use of NSP levels with xylanase supplementation in the rations of layers was examined. Xylanase supplement decreased FI in laying hens during 29–32 weeks of age (Nguyen et al., 2021). In contrast, Mirzaie et al. (2012) reported no significant interaction between the birds’ age and enzyme on FI of the laying hens fed with the xylanase-supplemented wheat-included diets. In the present study, no significant effect of the supplemental enzyme on the FI of laying hens was detected. The effects of dietary supplemental enzyme on ME of different cultivars of wheat can be partly influenced by the various nutrient levels as well as the quality and quantity of NSPs (González-Ortiz et al., 2016). In another report, the effects of supplemental enzyme on ME were affected by the birds’ age, with less impact on the performance of aged birds (Bedford, 2018).

In the present study, the laying hens fed with the diets supplemented with enzyme had less BWG compared to those fed with wheat-included diets with no enzyme. This might be partly due to the type of used enzyme (Ogunleye et al., 2019). In addition, the suggested enzyme matrix by manufacturer company was used in formulating the experimental wheat-included diets. It seems that the amount of AME of enzyme suggested by the manufacturer was higher than the actual amount or overestimated, which, in turn, had impact on the BWG of laying hens. In the study by Olgun et al. (2018), who evaluated the impacts of supplemental enzyme on the performance of laying hens fed with wheat- and corn-based diets, the BWG was adversely influenced by the dietary level of wheat. In another study, interactions between the dietary level of NSPs and supplemental enzyme on BWG of hens were observed during 29–32 weeks of age, so that xylanase improved the BWG of birds fed with low NSP diets compared to those fed with high NSP diet (Nguyen et al., 2021). In contrast, Mirzaie et al. (2012) reported no effect of wheat inclusion in the diet of layers on BWG. Rafuse et al. (2004) also found no significant effect of diet inclusion of wheat and enzyme on BWG. These variations in results can be partly due to the dietary level and variety of wheat, enzyme type and level and the birds’ age.

Egg quality traits

In the present study, egg-specific gravity and yolk index were not significantly affected by the diet inclusion of various wheat cultivars and enzymes. However, there was a significant effect of dietary treatments on the Haugh unit between some wheat cultivars on week 67. Rafuse et al. (2004) also reported no significant influence of dietary wheat cultivars and supplemental enzymes on egg quality traits in hens. Mirzaie et al. (2012) detected no significant effect of wheat cultivars and xylanase on the egg Haugh unit. Cufadar et al. (2010) found that egg-specific gravity, yolk index and the Haugh unit were not affected by the dietary inclusion of wheat and xylanase. Based on the study by Mirzaee et al. (2014), who evaluated the impacts of two different levels of diet AME and enzyme supplementation on the egg quality trait, the yolk index and the Haugh unit were not significantly affected in laying hens fed with diets contained two different wheat cultivars (Marvdasht and Sardari).

In the present study, eggshell weight (%) was higher in the layers fed with the enzyme-supplemented diets, including (week 67 of age). Additionally, the eggshell thickness was influenced by dietary treatments, with the highest thickness observed in the group fed with the Azar 2 cultivar. Eggshell strength in laying hens fed with xylanase-free diet decreased with age, but it remained constant in the group fed with the diet supplemented by xylanase during the trial period (Nguyen et al., 2021). In another research study, xylanase had no significant effect on eggshell weight but improved eggshell thickness in laying hens fed with wheat-included diets (Mirzaie et al., 2012). Better digestion and absorption of minerals in the gastrointestinal tract due to supplemental enzyme were considered the effective factors on the improvement of eggshell quality (Damen et al., 2012; Li et al., 2017; Wang et al., 2017). In contrast, Mirzaee et al. (2014) observed no significant impact of supplemental enzyme on eggshell weight and shell thickness in laying hens fed with wheat-included diets. Moreover, Lázaro et al. (2003) showed no significant effect of supplemental enzyme on the shell weight in laying hens fed with diets based on rye, wheat and barley. The discrepancy between the results of different experiments can be related to differences in dietary wheat cultivar, type and level of enzyme and age of birds.

In egg sampling at 62 weeks of age, egg shape index was higher in laying hens fed with the wheat-based diets supplemented by enzymes. The egg shape index, a scale in determining egg quality, presumably means an improvement of egg quality to be appropriately accepted by consumers (Ogunleye et al., 2019). The highest egg shape index in hens fed with the diet contained 40% wheat offal supplemented with enzyme compared to diet with no enzyme, which likely shows the positive impact of enzyme on egg shape index (Ogunleye et al., 2019). In contrast, Cufadar et al. (2010) found no significant effect of enzyme on egg shape index in layering hens fed with corn- or wheat-based diets. Mirzaee et al. (2014) also observed no significant changes in egg shape index in laying hens fed with enzyme-supplemented wheat-based diets.

In egg sampling at 62 weeks of age, the interactions between dietary wheat cultivar and enzyme on egg yolk and albumen weight were significant. According to the study by Nguyen et al. (2021), xylanase caused yolk weight loss at 32 weeks of age, with no significant effect in the early period of laying. This might be partly due to the reduced absorption of unsaturated fatty acids, the major component of egg yolk (Nguyen et al., 2021). In another study by Rafuse et al. (2004), no significant influence of dietary wheat cultivar and enzyme on egg yolk and albumen weight was detected. In the current study, lighter yolk colour was observed in the laying hens fed with diets with different wheat cultivars compared to corn-based diet. This can be as a result of the lower content of carotenoids in wheat compared to corn (Cufadar et al., 2010; Graham & Rosser, 2000). Adding enzyme to the diets of laying hens did not cause significant improvement in yolk colour. Roberts and Choct (2006) also showed that adding xylanase to the diet of laying hens fed with wheat-based diets had no impact on yolk colour. In contrast, Cufadar et al. (2010) found that the adding xylanase to the corn- or wheat-based diets increased yolk colour. Moreover, Pirgozliev et al. (2010) detected linearly increased yolk colour in laying hens fed with the xylanase-supplemented diets, including wheat or rye. It has been suggested that adding enzymes to the diet of laying hens decreases bile salt de-conjugation and increases fat digestion like carotenoids, as well as reduces the viscosity of digestive contents (Ciftci et al., 2003; Liu et al., 2017).

CONCLUSION

According to the findings of this study, the four Iranian wheat cultivars (Sardari, Azar 2, Pishgam and Sirvan) can serve as a suitable substitute for corn in poultry diets, without any adverse effects on productive performance (EP, EM and FCR) or most egg quality traits. However, there was a noticeable difference in yolk colour, as the groups fed with wheat-containing diets exhibited lighter yolks than those on the corn-based diet. Additionally, birds fed with certain wheat varieties exhibited a slight decrease in EW compared to those on a diet containing corn. Moreover, FI differed between diets contained various wheat cultivars, partly due to the differences in estimating the AME of the evaluated wheat varieties. Decreased BWG was detected in laying hens fed with diets supplemented with the commercial NSPase enzyme (beta-endopower), probably due to overestimating the enzyme matrix value used in formulating the experimental wheat-included diets with enzyme. The significant interactions between dietary wheat cultivar and enzyme were observed on egg yolk and albumen weight (p < 0.05). Moreover, eggshell weight (%) was higher in the layers fed with the enzyme-supplemented diets compared to the layers fed with diet without enzyme.

AUTHOR CONTRIBUTIONS

Data curation; investigation; resources; writing—original draft: SeyedKamyar Seyedoshohadaei. Conceptualization; project administration; resources; supervision; validation; writing—review and editing: Mehran Torki. Methodology; validation: Akbar Yaghoubfar. Formal analysis; software: Alireza Abdolmohammadi.

ACKNOWLEDGEMENTS

The authors appreciate Razi University for financially supporting the current study.

CONFLICT OF INTEREST STATEMENT

The authors have no conflicts of interest to be declared.

FUNDING INFORMATION

No funding was received to assist with the preparation of this manuscript.

ETHICS STATEMENT

All experimental protocols adhered to the guidelines, which were approved by the Animal Ethics Committee of the Razi University, Kermanshsh, Iran, and were in accordance with the EU standards for the protection of animals and/or feed legislation.

DATA AVAILABILITY STATEMENT

The related pure data file would be available at request.

TRANSPARENT PEER REVIEW

The peer review history for this article is available at https://publons.com/publon/10.1002/vms3.1202.