Effect of feed processing and enzyme supplementation of wheat-based diets on performance of broiler chicks

Abstract

An experiment was conducted using 336 one-day-old broiler chicks (Ross^® 308) to evaluate the effects of feed processing (pelleted vs. mash) and enzyme supplementation (with and without 0.3 g Grindazym GP 15,000/kg of wheat in a complete diet) on broiler chick performance from 1 to 36 days of age. Birds were randomly allocated to one of the four dietary treatments, each replicated four times (21 chicks per pen) in a completely randomised design in a 2×2 factorial arrangements. Measurements included body weight (BW), daily gain (DG), feed intake (FI), feed conversion ratio (FCR) and relative weight of gastrointestinal organs to BW (%). Results showed that the broiler chicks fed the pelleted diets had significantly (P < 0.05) improved BW, DG, FI and FCR. In addition, birds fed the diet containing the enzyme supplement had significantly (P < 0.05) improved BW, DG, FI and FCR; however, the beneficial effects of the enzyme were mainly limited to earlier stages of growth. There was a significant interaction between feed processing and enzyme supplementation for FCR between 20 and 36 days. Neither feed processing nor enzyme supplementation had significant effects on carcass or gastrointestinal characteristics, except gizzard weight relative to BW at 36 days of age. In conclusion, the results of this experiment show that both pelleting and enzyme supplementation are valuable tools to improve broiler chicks performance and feed utilisation which is plays a crucial role in reducing feed supply shortage in developing countries.

Keywords:

• broiler
• body weight
• enzyme
• pellet
• feed conversion ratio

Introduction

Although corn is a preferred grain source in broiler diets it is not always available at a reasonable price in many countries. In such situations, wheat may be a more viable alternative, especially when the price difference between corn and wheat is favourable. Compared with corn, wheat has lower energy content, but is richer in many other nutrients including protein and amino acids such as lysine, methionine, arginine, phenylalanine and tryptophan (NRC 1994).

Unfortunately, all major wheat-producing countries report considerable variability in wheat energy content, mainly due to high variation in content of complex, highly viscous and water-soluble non-starch polysaccharide (NSP) (Choct and Annison 1990; Anisson 1993; Chesson and Austin 1998). Water-soluble NSP is not only indigestible but also interfere with the process of digestion, thereby reducing availability of all nutrients but especially fat and as a result energy. Arabinoxylan (50–80 g/kg) is the predominate NSP in wheat, consisting of a main chain of β(1,4) linked xylose residues to which side chains of α-arabinose are substituted at the O₂ and O₃ positions (Annison 1993).

Poultry do not synthesise enzymes capable of hydrolysing such cereal structural carbohydrates but do support microorganisms in the large intestine and caecum that have this capability. Therefore, enrichment of their diets with exogenous enzymes with appropriate activities is of importance in practical feeding especially in young broiler chicks that have a relatively low capacity for hind gut fermentation (Boros et al. 1998; Zhang et al. 2000). Exogenous enzymes are able to minimise the adverse effects of soluble NSP; and consequently improve feed utilisation and as a result reduce environmental impact of poultry production (Choct and Annison 1990; Bedford and Morgan 1996; Classen 1996; Pan et al. 1998; Zanella et al. 1999; Hughes et al. 2000; Zhang et al. 2000; Svihus and Hetland 2001; Wang et al. 2005).

Grinding serves as a physical processing method to disrupt the physical structure of dietary ingredients and thereby increase the surface area exposure to digestive enzymes. A combination of heat and moisture treatments by steam pelleting, expansion or extrusion is used to gelatinise starch to improve its digestibility, degrade or inactivate anti-nutritive factors, such as α-amylase inhibitors but it also results in formation of resistant starch and solubilised NSP (Chesson and Austin 1998) both of which detract from digestibility. Nevertheless, it has been reported (Salari et al. 2006) that chickens fed pelleted diets gained more weight, consumed more feed and converted feed more efficiently but also deposited significantly more abdominal fat.

While the benefits of feeding pelleted diet over mash diet are well documented more work is needed to determine whether the response to application of exogenous enzyme is influenced by type of feed processing method diets (Alzueta 1991; Al Bustany 1996). Therefore, the objective of the present study was to determine the effect of feed processing method (pelleted vs. mash) on the response of broiler chicks to enzyme supplementation in a diet rich in wheat.

Materials and methods

This study was carried out at the Animal Science Department, University of Kurdistan, Sanandaj, Iran. A total of 336 one-day-old Ross 308 broiler chicks (mixed sex) were used to evaluate the effects of feed processing method (pelleted vs. mash) and enzyme supplementation (with and without 0.30 g Grindazym GP 15,000/kg of wheat in complete diet) in a wheat-based diet on broiler chicks performance from 1 to 36 days of age. Each group consisted of four replicates of 21 birds (per each replicate). Experimental diets were formulated to meet or exceed the nutrient requirements (NRC 1994) of the broiler (Table 1). The enzyme preparation (Grindazym GP 15,000: 15,000 BGU/g endo − 1, 4-beta-glucanase EC 3.2.1.4., 36,000 FXU/g endo − 1, 4-beta-xylanase EC 3.2.1.8.) was obtained from the Biochem Company (Biochem-Co. Ltd. No. 267, Gholsang Saiediehe Station, Bahonar av. (ex. Niavaran, 19356 Tehran, Iran). Pelleted feed was prepared in a local feed mill (Jik-Daneh Co., Greza Kamarbande, Jihad Square, Sanandaj, Iran) using a short-term conditioner (15 s retention time) set at low temperature (35°C) and low steam injection (to increase diet moisture up to 10%) and the diet pelleted through 2 and 3.17 mm dies (Sprout Matador A/S, Esbjerg, Denmark), for starter and grower diets, respectively. The pelleting temperature was deliberately kept low to minimise losses of enzyme activity. The chicks were housed in 16 floor pens (1.25×1.4 m), containing wood shavings throughout the experiment. Light was on continuously for the first day post-hatching, after which a 23 L: 1 D lighting schedule was maintained for the duration of experiment. Temperature was maintained between 30 and 32°C at the beginning of the rearing period and was gradually decreased every 2–3 days to 22°C at the end of rearing period. Chicks were provided free access to feed and water during the experiment. Care and management of the chicks were in accordance with commercial guidelines and protocol approved by University of Kurdistan Animal Ethic Committee.

Table 1. Composition and nutrient levels of the basal diets.

Ingredient (g/kg)	Starter (0–21 days)	Grower (22–36 days)
Wheat	565.2	601.9
Soybean meal (440 g Cp/kg)	349.2	310.8
Fish meal (63% Cp)	15.0	5.0
Soy oil	34.7	45.8
CaCo3	10.0	10.0
Dicalcium phosphate^a	15.3	15.3
Common salt	2.7	2.8
Mineral premix^b	2.5	2.5
Vitamin premix^c	2.5	2.5
dl-methionine	2.1	2.3
l-lysine—HCL	0.8	0.9
Calculated analysis (g/kg) ^d
ME (mJ/kg)	12.14	12.56
Crude protein	222.3	203.4
Ca	9.4	8.8
Total phosphorus	6.9	6.6
Non-phytate phosphorus	4.5	4.2
Methionine	5.4	5.3
Total sulfur amino acids	9.1	8.8
Lysine	13.3	11.9
Na	1.5	1.5
^aContain 250 g/kg Ca and 180 g/kg P.
^bProvides per kilogram of diet: vitamin A (9000 IU), vitamin D3 (2000 IU), vitamin E (18 IU), menadion (2 mg), thiamine (1.8 mg), riboflavin (6.6 mg), niacin (30 mg), pyridoxine (3 mg), vitamin B12 (15 mg)[AQ18], d-pantothenic acid (100 mg), folic acid (1 mg), biotin (0.1 mg), choline chloride (500 mg) and antioxidant (100 mg).
^cProvides per kilogram of diet: manganese (100 mg), zinc (84.7 mg), iron (50 mg), copper (10 mg), iodine (1 mg) and selenium (0.2 mg).
^dCalculated and based on published tabular values for individual ingredient (NRC 1994).

Birds were weighed as a group on arrival. At 20 and 36 days of age, all birds were weighed by pen. Feed intake (FI) was recorded at the same points in time and used for calculation of feed conversion. Mortality was recorded daily and feed consumption data were corrected for body weight (BW) of mortality. Average BW, daily gain (DG), FI and feed to gain ratio (FCR) were determined for each period and for the overall experiment.

Two birds per pen (eight birds/treatment) were randomly selected for gastrointestinal measurements on 20 and 36 days of age, while feeding normally. The chicks were weighed, killed by cervical dislocation, and abdominal cavity opened. The proventriculus, gizzard, liver and small intestine were separated, and weights of liver (without gall bladder), proventriculus, gizzard (after digesta removal) and three different sections of small intestine (duodenum, jejunum and ileum) were recorded and their relative weight (RW) (g 100/g) to BW was determined. At 20 days of age, the lower small intestine tract digesta content (from yolk stalk to ileo cecal junction) of two birds which had been used for gastrointestinal measurements were collected and pooled for pH measurements using a digital pH meter (Model 744, Metrohm Ion Analysis, Metrohm CH-91 01 Herisau, Switzerland).

Data were analysed as a 2×2 completely randomised design with processing method and enzyme as the factors using the general linear models procedure (SAS 2001). Significant differences among treatments (Duncan's multiple range test) were accepted if P ≤ 0.05.

Results

Bird performance

The results of this study showed that birds fed pelleted diet had significantly (P < 0.05) higher BW at 36 days of age, higher DG between 20 and 36 days of age and higher FI throughout all experimental periods (Table 2). The feed conversion ratio (FCR) significantly (P < 0.05) increased for birds fed the pelleted versus mash diet between 0–20 and 0–36 days of age (Table 2).

Table 2. The effect of feed processing and enzyme supplementation on BW and weight gain in broiler chicks.

	Feed processing (P)		Enzyme (E) (g/kg)		P-value
Days	Pelleting	Mash	0	0.30	P	E	P×E	SEM
Body weight (g)
20	630.9	611.1	597.4^b	644.6^a	0.2447	0.0312	0.1077	32.4789
36	1955.6^a	1791.4^b	1796.0^b	1950.9^a	0.0012	0.0019	0.9769	78.0922
Daily gain (g)
0–20	29.9	28.9	28.2^b	30.6^a	0.2502	0.0137	0.0884	1.6323
20–36	82.0^a	74.4^b	74.8^b	81.6^a	0.0035	0.0068	0.3287	4.1567
Feed intake (g/day^−1)
0–20	51.9^a	46.6^b	48.0^b	50.5^a	<0.0001	0.0120	0.2515	1.7055
20–36	153.8^a	137.8^b	141.5	150.1	0.0021	0.0584	0.3505	8.2179
0–36	94.7^a	85.8^b	87.6^b	92.9^a	0.0013	0.0283	0.2947	4.2319
Feed conversion ratio(g/g^−1)
0–20	1.74^a	1.62^b	1.71	1.65	0.0044	0.1624	0.1624	0.0722
20–36	1.88	1.86	1.89	1.84	0.6418	0.1595	0.0143	0.0733
0–36	1.83^a	1.77^b	1.83^a	1.78^b	0.0214	0.0267	0.0513	0.0416
Note: Mean values within a row and under each main effects with no common superscripts differ significantly (P < 0.05).

The results showed that incorporation of the enzyme in the diet resulted in higher BW at 20 and 36 days of age (Table 2) and higher DG between 0–20 and 20–36 days of age. Using enzyme in the present experiment also improved broiler FI between 0–20 and 0–36 days of age and FCR throughout the experiment (P < 0.05).

The interaction between processing method and enzyme supplementation was only significant for FCR between 20 and 36 days of age, as shown in Figure 1, the addition of enzyme to the mash diet significantly (P < 0.05) improved FCR (Figure 1) but had no effect on FCR in for birds fed the pelleted diet (P > 0.05).

Figure 1.  The interaction between feed processing (mash vs. pelleted) and enzyme supplementation (with or without 0.30 g Grindazym GP 15,000/kg of wheat in complete diet) on FCR (g/g) during 20–36 days of age.

Ileum pH and gastrointestinal traits

Neither feed processing method nor enzyme supplementation had significant effects on the pH of broiler ileum digesta (data not shown) or on the weight of the different gastrointestinal tract organs relative to BW (g 100/g) at 20 and 36 days of age, with the exception of gizzard, pancreas and duodenal relative weight (RW) at 36 days (Table 3). At this age, gizzard RW (%) was significantly lower in birds fed pelleted versus mash diets (1.04 vs. 1.46% in mash diet). As shown in Figure 2, enzyme supplementation of the pelleted diet resulted in significantly (P<0.0587) higher pancreas RW (%) at 36 days of age whereas there was no such enzyme effect on mash-fed birds t (P>0.05). Pelleting the diet increased duodenum RW (%) only in diets which did not contain enzyme at 20 days of age (Figure 3). Broiler carcass characteristics (Table 4) were not significantly (P>0.05) affected by any of the dietary treatments.

Figure 2.  The interaction between feed processing (mash vs. pelleted) and enzyme supplementation (with or without 0.30 g Grindazym GP 15,000/kg of wheat in complete diet) on pancreas RW (%) at 36 days of age.

Figure 3.  The interaction between feed processing (mash vs. pelleted) and enzyme supplementation (with or without 0.30 g Grindazym GP 15,000/kg of wheat in complete diet) on duodenum RW (%) at 20 days of age.

Table 3. The effect of feed processing and enzyme supplementation on RW (g 100/g) of gastrointestinal organs to live BW at 20 and 36 days of age in broiler chicks.

	Feed processing (P)		Enzyme (E) (g/kg)		P-value			SEM
	Pelleting	Mash	0	0.30	P	E	P×E
Duodenum RW
20 days	1.36	1.29	1.32	1.32	0.3713	0.9741	0.0364	0.0754
36 days	0.92	0.85	0.88	0.89	0.4688	0.9396	0.4252	0.0969
Jejnum RW
20 days	2.61	2.44	2.57	2.47	0.1924	0.4324	0.8116	0.1231
36 days	1.86	1.88	1.91	1.84	0.9402	0.7427	0.7084	0.2121
Ileum RW
20 days	1.82	1.69	1.70	1.80	0.3119	0.4539	0.7607	0.1243
36 days	1.42	1.40	1.50	1.33	0.8959	0.1843	0.3288	0.1216
Liver
20 days	2.88	3.06	3.0	2.94	0.4338	0.8310	0.9377	0.2350
36 days	2.87	2.68	2.76	2.78	0.5450	0.9147	0.7483	0.2970
Pancreas
20 days	0.39	0.40	0.39	0.39	0.6710	0.9074	0.8464	0.0316
36 days	0.27	0.27	0.26	0.27	0.9257	0.7799	0.0205	0.0262
Proventriculus
20 days	0.57	0.64	0.63	0.59	0.2693	0.4753	0.8207	0.0594
36 days	0.37	0.35	0.34	0.38	0.4309	0.2761	0.0854	0.0307
Gizzard
20 days	1.81	2.14	1.97	1.98	0.1644	0.9524	0.3251	0.2254
36 days	1.04^b	1.46^a	1.34	1.15	0.0035	0.1316	0.3368	0.1174
Note: Mean values within a row and under each main effects with no common superscripts differ significantly (P<0.05).

Table 4. The effect of feed processing and enzyme supplementation on carcass characteristics (g 100/g) in broiler chicks at 36 days of age.

	Feed processing (P)		Enzyme (E) (g/kg)		P-value
	Pelleting	Mash	0	0.30	P	E	P×E	SEM
Processed carcass	67.8	62.2	60.7	69.3	0.3257	0.1388	0.3860	5.4574
Breast	23.5	20.8	20.5	23.8	0.1521	0.0884	0.3602	1.7988
Thighs	10.4	9.6	9.3	10.7	0.4462	0.1895	0.3671	1.0030
Drums	8.9	8.3	8.1	9.1	0.5189	0.2552	0.4337	0.7731
Abdominal fat	1.37	1.25	1.34	1.29	0.5143	0.7905	0.4969	0.1748
Note: Processed carcass equals the sum of all parts excluding abdominal cavity contents.

Discussion

The objective of the present study was to evaluate the effects of feed processing method on broiler chick response to enzyme supplementation and possible interaction between them on broiler performance.

Predictably, pelleting broiler diets resulted in superior performance in almost all aforementioned performance criteria. These findings are in agreement with published reports claiming that pelleted feed is thought to increase animal performance due to decreased feed loss at the feeder, reduced animal energy expenditure during consumption and decreased ingredient segregation (Kilburn and Edwards 2001; McKinney and Teeter 2003; Greenwood et al. 2004; Moritz et al. 2005; Salari et al. 2006). McKinney and Teeter (2003) reported that pelleting contributes the equivalent of 187 kcal metabolizable energy (ME)/kg at 100% pellet quality, with the caloric value of the pellets diminishing with decreasing pellet quality. Moritz et al. (2005) reported that diets containing pelleted or extruded corn increased live weight gain compared with the control in part due to increased FI. Greenwood et al. (2004) showed that pellet-fed birds consume significantly less digestible lysine to achieve the same amount of BW gain as the mash-fed birds, suggesting that the effect is not restricted to intake. The fact that pelleting reduced gizzard RW (%) at 36 days of age in the present study suggests that less energy was expended in grinding feed particles, and consequently improving throughput (i.e. FI) and consequently performance.

The findings of the present experiment on enzyme effects on broiler performance are in agreement with those showing improved broiler performance by enzyme supplementation of diets (Preston et al. 2001; Wang et al. 2005). The benefits of exogenous enzyme supplementation to NSP-rich diets are well documented. These enzymes can partially hydrolyse NSP, reduce viscosity of gut contents, and result in improvements in nutrient absorption (Choct and Annison 1990; Annison 1993; Zhang et al. 2000).

The lack of an interaction between processing method and enzyme supplementation may be partially related to the relatively low temperature applied in this study (35°C). McCracken et al. (1993) reported both decreased excreta dry matter content and increased digesta viscosity when feeding broiler chickens with feeds pelleted after conditioning at 85°C for 15 min compared with cold pelleted feeds. Inborr and Bedford (1994) also showed that conditioning the diets at 75 and 85°C resulted in almost identical overall bird performance but both live weight gain and feed utilisation were significantly worse after conditioning at 95°C before pelleting. In both studies, the inference was that the application of a viscosity reducing enzyme would have been more beneficial at higher rather than lower pelleting temperatures.

Conclusions

In conclusion, the results of this experiment confirmed the beneficial effects of pelleting and feed enzyme supplementation on broiler chicks' performance; however, it seems that they both influence performance independently and indeed may interact under certain circumstances.

Acknowledgements

The authors wish to express thanks to the University of Kurdistan for funding this research project. We would like to thank Dr Michael Bedford (AB Vista Feed Ingredients Ltd, 3 Woodstock Court, Blenheim Rd, Marlborough SN8 4AN, UK) for great assistance in editing and proof reading of the manuscript. The authors also express their gratitude to Biochem Company for providing the enzyme used.