عنوان مقاله [English]
Introduction: Agricultural by-products, which contain high fibre and have low nutritional value, are one of the feed sources for ruminant animals. A variety of cereal residues including wheat straw, corn stover and paddy straw are generally used to supplement the green forage as animal feed. Wheat is an important cereal crop, which generates a huge amount of lignocellulose in the form of straw. Some various strategies have attempted to improve forage quality. These methods include physical treatments (heat, steam and pressure) as well as treatment with chemical treatments such as acids, alkalis, NH3 and ozone. However, using them is associated with some problems as they require complex material and have detriments such as secondary pollution. Recently the researches have focused on biological alternatives, especially since they are environmentally benign and widely acceptable. One of the biological methods is to use micro-organisms including fungi and bacteria many of which had been found to degrade cellulose and other plant cell wall fibers. The cellulase activity of the fungus is premier, whereas bacteria have a faster growth rate than fungi, and there is increasing interest in cellulase production by bacteria and they can generate cellulase much better. Cellulolytic bacteria are present in a variety of sources such as composting heaps, decaying agricultural wastes, soil and gastrointestinal tract of herbivores. These bacteria are presumed to live in both the rumen and in the colon that digest plant cell walls. Annually, large amounts of agricultural residues are produced in countries around the world, including Iran. These agricultural residues are important foods in the diet of ruminants. However, the use of these products as a food source in the diet of ruminants is limited due to their limited biological structure and low protein. Different physical, chemical and biological methods have been used to process wheat straw, all of which aim to break down lignin and make more cellulose and hemicellulose available for fermentation in the rumen. The use of biological processing method by fungi has received more attention due to the lack of environmental pollution. White rot fungi are the only organisms that are able to aerobically break down lignin into CO2 and water. Schizophyllum commune is an edible fungus of the basidiomycete’s family. Spraying of lacase enzyme from Schizophyllum (liquid culture lacase, solid culture lacase and purified lacase) on wheat straw, corn straw and sorghum straw gradually reduces the amount of Neutral Detergent Fiber of straws and As a result, it increases the digestibility of straws. Lignin is an important constituent of these agro-residues which is resistant to most of the bacterial enzymatic systems, as well as non-digestible by ruminants and rumen microflora. Solid state bioprocessing of agro residues by ligninolytic fungi have got the potential to convert these materials into better feed. Beside lignin, these agro residues contain complex polysaccharides (hemicellulose and cellulose) and water-soluble fractions (soluble sugars, some pectin component, some soluble proteins and organic acids). Lignin binds with hemicellulose and cellulose to form a matrix and make these polysaccharides unavailable for the ruminants. Bio delignification of agro-residues has got the potential to convert this biomass into more nutritive and easily digestible feed. Most studied white rot fungi species are quite efficient lignin degrader but it also degrades an enormous amount of organic matter thus limiting its practical use for improvement of animal feed quality. while the pretreated straw may be useful for other purposes including biofuel production. It necessitates the need to look for organisms which can degrade the lignin without causing major loss of other important constituents like hemicellulose and cellulose. The purpose of this experiment was to determine the chemical composition, volume of gas produced, dry matter degradability, degradability of Neutral Detergent Fiber and volatile fatty acids produced by wheat straw processed with Schizophyllum commune under liquid culture and solid culture using nylon bags and gas production method.
Material and Methods: To process wheat straw, the straw was first soaked in water for 12 hours and then sterilized in an autoclave at 121 ° C for 20 minutes. For solid culture, a 7-day-old mushroom was transferred to each jar containing sterilized wheat straw and stored at 26 ° C for 25 days. Liquid culture medium containing the secreted enzymes was inoculated after filtration of the fungi on the liquid and into a glass chamber containing sterile and soaked wheat straw and kept at 26 ° C for 25 days. Wheat straw was removed from the jars after 25 days and dried for 4 days at 60 ° C. The gas production of the treatments in glass vials at 2,4,6,8,12,24,48,72,96,120,144 hours and their degradability were measured using nylon bags and three Holstein cows fistulated at 2,4,6,8,12,24,48,72,96 hours of ruminal incubation.
Results and Discussion: Processing of wheat straw by Schizophyllum commune reduced dry matter and Neutral Detergent Fiber. Solid culture and liquid culture increased the amount of protein from 2.94 to 6.12 and 5.7%, respectively. Cumulative gas production increased during 144 hours of incubation in wheat straw processed by solid culture. Organic matter digestibility percentage, dry matter digestibility percentage and Metabolisable energy in wheat straw processed by liquid culture method showed a significant increase. The amount of crude microbial protein in wheat straw processed by liquid culture method showed a significant increase. Dry matter degradability increased during 96 hours of ruminal incubation and the potentially fermentable portion of processed wheat straw by solid culture. There was no significant difference between different treatments in terms of nutritional value index. The degradability of Neutral Detergent Fiber was reduced during 96 hours of incubation and the effective degradability in the treated groups was reduced. Liquid and solid culture processing increased the total amount of volatile fatty acids and ammonia nitrogen in wheat straw.
Conclusion: In general, processing of wheat straw with Schizophyllum by solid culture method improved some nutritional components, but the addition of fungal liquid culture medium did not have a significant positive effect on increasing the nutritional value of wheat straw.