| Energy feed shortage is a major problem all over the world. China is the leading crop straw producer in the world, and the straw yield accounts for half of the biomass resources. It can realize the use of renewable resources, relieve the energy resources crisis, protect the environment and realize the sustainable development of agriculture and economy by the economic and effective utilization of straw. With the rising price and shortage of corn, the main energy feed in animal production, it is imminent to convert straws into animal feed.In this study, the pretreatment and microbial fermentation was combined in developing the biological fermentation of corn stalk (BFCS). Study on its nutritional value and effect on production performance of broiler was conducted. The results were as follows:(1) The effect of different physical and chemical pretreatments on corn stalk degradation was studied. The results showed that the optimum condition of corn stalk pretreatment was air dry corn stalk exploded directly under 2.5 Mpa pressure for 200 s. The degradation rates of cellulose, hemicelluloses and lignin in the corn stalk were 8.47%, 50.45% and 36.65%, respectively. The pretreatment was practical and suitable for the subsequent microbial fermentation.(2) To study the combined effect of physical and biological treatments on corn stalk degradation, microstructure, composition and enzyme productions, the corn stalk was steam exploded (2.5 Mpa, 200 s), and then followed by microbial fermentation. The results showed that microbial fermentation could reduce the contents of cellulose in original and exploded stalks significantly (P<0.05). NDF and ADF contents in the exploded corn stalk fermented by Aspergillus oryzae was significantly lower than that fermented by Trichoderma koningii (P<0.05), which indicated Aspergillus oryzae fermentation was more effective than Trichoderma koningii for the insoluble fiber degradation. After the exploded corn stalk was fermented by Aspergillus oryzae for 6 days, the contents of cellulose and hemicellulose in the fermented corn stalk were decreased by 27.89% and 64.80% respectively, compared with the original corn stalk (P<0.05). The filter paper cellulase, CMCase, amylase and protease activities in the fermented products were 335.10, 1138.92, 32.57 and 201.99 U/g, respectively. The content of formic acid in the fermented products was lower than that in the exploded stalk, and furfural in the fermented products was all degraded, which indicated that fermentation treatment effectively reduced the content of inhibitors produced in the pretreatment. The microstructure was analyzed by scanning electron microscope, the surface of untreated corn stalk was smooth and tightly complete. There were many spherical structures on the surface of exploded corn stalk, indicating explosion treatment made the lignin in corn stalk rearrangement to increase the specific surface area. The fermentation of exploded corn stalk by Aspergillus oryzae made the tissues broken, and more internal fibrous exposed, which contributed to the utilization of animals. The corn stalk pre-treated by steam explosion and followed by Aspergillus oryzae fermentation seems to be a new prospective method for corn stalk degradation and application.(3) The four-factor and three-level orthogonal experiment was used to determine the optimum fermentation prescription of exploded corn stalk. The result showed that the optimal medium for biodegradation of exploded corn stalk was 5% corn meal, 2.5% wheat bran, 5% soybean meal and 4% the nutrient solution. The levels of nutrient solution, corn, and soybean had significant effect on stalk degradation (P<0.05).(4) Substitution method and emptying-force-feeding method were used to determine the apparent metabolic energy of BFCS separately. In substitution method, a total of 16 AA broilers were assigned to 2 groups, 8 broilers for each group. Group 1 was fed with the basal diet (consist of 8% BFCS); group 2 was added with 30% BFCS to replace the same percent of energy and protein feed in the basal diet. The results showed that the apparent metabolic energy (AME) of broiler in basal diet is 12.63 MJ/kg, AME of BFCS predicted by the formulation of basal diet was 12.46 MJ/kg,which was 4.38 MJ/Kg calculated by the formula. In emptying-force-feeding method, a total of 10 AA broilers were assigned to 2 groups, 5 broilers for each group. Group 1 was added with the BFCS; and group 2 was added with exploded corn stalk. The result showed that AME of broilers in group1 and group 2 was 5.30 and 6.33 MJ/kg, respectively.(5) A 2-period feeding program was adopted in the experiment to study the effect of BFCS for replacing corn meal on broiler production, and to get the suitable substitution rate for broiler farming.In the earlier stage (1-21 d), a total of 200 one-day-old AA broilers were assigned to 5 groups, 40 broilers for each group consisting of 4 replicates. In the later stage (22-42 d), a total of 150 22-day-old AA broilers were assigned to 5 groups, 30 broilers for each group consisting of 5 replicates. The control group was the basal diet; group 1, 2 and group 3 was added with 4%, 8% and 12% BFCS for replacing the same percent of corn meal in the basal diet, respectively. Group 4 was added with 8% BFCS for replacing the same percent of corn meal in the basal diet, and the energy was balanced with the control.In the earlier stage, the results showed that the average daily gain (ADG) and the feed conversation (FCR) were decreased significantly in the groups added with BFCS (P<0.05); the organic matter, energy and protein metabolic rates in group 3 were lower than that in the control group (P<0.05). The counts of lactic acid bacteria in the ileum and cecum in group 3 was reduced, compared with the control group (P<0.05). The serum uric acid content in group 3 and 4 was higher than that in the control (P<0.05). The activities of filter paper enzyme, CMC enzyme in duodenum and the filter paper enzyme in cecum in group 2 were higher than that in the other group (P<0.05). Economic benefit of the groups added with BFCS were reduced, compared with the control.In the later stage, the feed intake was improved in group 1 and group 2 (P<0.05); metabolic rate of NDF and ADF in group1 and group 2 were significantly higer than that in the control group (P<0.05); lactic acid bacteria counts in ileum and cecum of group 2 was increased significantly (P<0.05). The activities of filter paper and CMC enzymes in duodenum and cecum in group 2 were higher than that in the control group (P<0.05). The average daily gain (ADG) was improved in group 2, 3 and 4 (P<0.05); the energy metabolic rate was reduced in group 3 (P<0.05); lactic acid bacteria counts in ileum and cecum of group 3 were significantly lower than that in group 2 (P<0.05); relative weight of duodenal and ileum were improved in group 3. The serum total protein, albumin and globin were improved in group 5 (P<0.05), lactic acid bacteria counts in ileum and cecum were increased significantly in group 5 (P<0.05), the red degree of pectorals in group 5 was also increased. The economic benefit in group 1 was higher than that in the control group, the economic benefit in group 2 was comparable to that in the control, and was higher than that in group 4.In conclusion, 4-8% BFCS to replace corn meal in the diets of broilers at later feeding stage could improve production performance of broilers, and the application of BFCS in animal production is an economic and feasible way.
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