عنوان مقاله [English]
Introduction Corn is one of the most important cereals used for poultry feeding due to its high starch, available energy and protein. Starch is an important source of energy in cereals and it is important to pay attention to its availability. In the cell wall of the endosperm, cereal grains, contain some of the structural carbohydrates that are soluble in the small intestine and have high molecular weight which may cause viscosity. Positive physical and chemical changes by steam conditioning, include starch gelatinization, denaturation of digestive enzyme inhibitor proteins, and cell wall breakage. Regardless of NSP content, some amounts of nutrients pass through the birds gut without being digested in corn-soy diets. Supplementing broiler diets with exogenous enzymes to degrade NSP has been a useful tool to release energy and nutrients, which can increase the value of low quality corn in poultry feeds and improve growth performance.
Materials and Methods This project was conducted at the Poultry Research Center of Ferdowsi University of Mashhad. A batch of corm grains was obtained from a commercial supplier and ground in a hammer mill to pass through screen sizes of 3.0 and 5.0 mm for starter (1-10 d) and grower (11-24 d) periods, respectively.
First trial: Apparent metabolizable energy (AME) and digestibility of corn crude protein (CP) and dry matter (DM) were determined in basal diets, which the corn was the sole source of ME and CP. Basal diets contained the conditioned (at temperatures of 55, 70 and 85 °C) or unconditioned corn and was or was not supplemented with enzyme (Rovabio®; Adisseo, France) at the amount of 0.5 g/kg diet. Total excreta collection was performed with 144 chicks in 8 treatments with 6 replicates and 3 birds each, during 7 to 9 days of age using battery cages. Excreta from each replicate cage were collected early in the morning and in the evening. After removing feathers, feed residues, and other contamination sources, excreta were air dried in an oven at 55 °C for 72 hours. Then the excreta were weighed and homogenized, then a sample of approximately 30% of the excreta was randomly separated and kept at -20 °C to further analysis. Then, dried excreta samples were ground in a micro-mill and submitted to the Animal Nutrition Lab. Feed and excreta dry matter, gross energy, and nitrogen contents were determined.
Second trial: In second trial, 576 d-old broilers from Ross 308 strain with initial BW of 43 g, were fed with mash diets containing conditioned corn which was or was not supplemented with enzyme, during starter (1-10 d) and grower (11-24 d) periods. The experiment was done based on a completely randomized design with 4 × 2 factorial arrangement of treatments evaluating four corn conditioning temperatures (unconditioned and conditioned at 55, 70 and 85 °C) and two enzyme (Rovabio®; Adisseo, France) levels (0 and 0.5 g/kg diet). chicks were assigned under eight treatments with 6 floor pen replicates. Each floor pen of 1.2 × 1 × 0.8 m (L × W × H) included 12 chicks (6 male and 6 female, equally for all replicates). Floor pens were covered with 1.5 Kg/m2 of wood shavings. Four of eight experimental diets were supplemented with 0.5 g/kg of a multiple enzyme complex composed of cellulases, 6400 unit; β-glucanase, 2000 unit and Xylanase 22000 unit per gram (Rovabio®; Adisseo, France). Corn-soy-based diets were formulated to meet the Ross 308 strain recommendations for major nutrients for starter and grower phases. Feed and water were supplied for ad libitum consumption throughout the trial with a tube feeder and two nipple drinkers in each floor pen. House temperature was initially set at 32 ◦C on day one and was decreased linearly by 0.5 ◦C per d to a temperature of 21 ◦C. During the experiment, the lighting program consisted of 23L:1D. A completely randomized design with 4×2 factorial arrangement was used in the both trials. Main factors were included corn conditioning temperatures (unconditioned and conditioned at 55, 70 and 85 °C) and two enzyme levels (0 and 0.5 g/kg diet). The data were analyzed using generalized linear model (GLM) procedure, SAS software (9.4) and the differences between them was tested by Duncan's test (P ≤ 0.05).
Results and Discussion Conditioning and enzyme supplementation had no significant effects on AME and CP digestibility. Conditioning at 80 °C decreased DM digestibility of corn in comparison to control group (P<0.05). Enzyme had no significant effect on DM digestibility. In second trial, there were no significant differences in productive performance among treatments during 11-24 d and the accumulated period (1 to 24 d). Feed conversion ratio (FCR) of the birds fed diets containing conditioned corn at 85 °C was significantly more than that of 55 and 70 °C diets during 1-10 d; although it was not significantly different with control group. Neither corn conditioning nor enzyme supplementation had significant effect on carcass characteristics, and small intestine segments length and weight at 24 d. Enzyme supplementation significantly increased villi height and width at 24 d (P < 0.05). Corn conditioning significantly increased villi width and crypt depth but decreased villi width to crypt depth ratio. Bifidobacteria, E. coli and clostridia population in the ileal contents were not affected by corn conditioning and enzyme supplementation. Lactobacillus population was increased by enzyme addition and also by corn conditioning at temperature 70 °C in compare to control group. These results are in agreement with those reported by Gonza´lez-Alvarado et al. (2007) who reported no significant differences in growth performance of broiler chicks fed heat treated corn-based diets. However, negative effect of higher pelleting temperatures on the WG of birds fed corn-based diets have also been reported. They showed that pelleting a corn–soybean meal diet at 65 ◦C resulted in higher weight gain compared to the basal mash diet and diets pelleted at 75 and 85 ◦C.
Conclusion In general, corn conditioning and enzyme supplementation did not improve growth performance and nutrient utilization but improved gut histomorphology and microbial status.