Improving digestibility and palatability of straw feed by separating lignocellulose decomposition and lactic acid bacteria fermentation

Abstract: In China, about 7.0×108 t of crop straws may be collected annually, and the amount suitable for converting to feed was approximately accounted for 85.67%. However, low digestibility and protein content prevent its use in feedlots, much of these materials were disposed by burning, which resulted in environmental pollution. A matrix formed by lignin and hemicellulose surrounds the orderly cellulose microfibrils and reduces their digestibility. The breakdown of the bonds between lignin and cellulose is the key to transform the lignocellulosic substrate into a high quality feed for ruminants. Studies have provided various results that removal of lignin enhanced the digestibility of straws. Although hemicellulose has higher potential digestibility than the other cell wall components, its degradation was not maximized because it concentrated in the primary wall, and no research results has been provided that the removal of hemicelluloses enhanced the digestibility. In order to improve the digestibility and nutrition value of air-dried corn stalk, and to develop a convenient and practical straw feed processing technology, experiments were carried out as follows: 1) Corn stalk was fermented at 60℃ in a feed fermentation machine for 5 days, after the moisture content of which was adjusted to 60%, and hemicellulose-degrading microflora WDC2 was inoculated in them; 2) Lactic acid bacteria community S FC-2 was cultivated in a fermentation tank, the working volume of which was 30 L; 3) Culture broth of SFC-2 was sprayed evenly on the corn stalk being partially degraded, at the rate of 1:1 (m/v) to produce fermented straw feed. In this study, the feasibility of bioconversion of straw as forage by dividing the fermentation into lignocellulose decomposition of corn stalk and malolactic fermentation of lactic acid bacteria, was discussed from the nutriology and the molecular ecology. The results indicated that after 5 days high-temperature fermentation, the degradation rates of cellulose, hemicelluloses and lignin were 5.36%, 18.83% and 3.29%, respectively, and in vitro digestibility of dry matter, neutral detergent fiber and acid detergent fiber improved by 13.94%, 22.56% and 21.12%, respectively. In addition, dry matter, crude protein and water soluble carbohydrate content, as well as in vitro degradation rate showed that the quality of products was stable during the continuous fermentation. The results of PCR-DGGE indicated that the diversity of microorganisms in the decomposed straw was very abundant, however, no pathogenic bacteria was detected. Meanwhile, during the continuous fermentation of lactic acid bacteria, the microbial composition of the lactic acid bacteria community, OD600 and pH value of the culture broth were all stable. However, lactic acid and ethanol content were decreased and acetic acid was increased as the cultivate time. Which indicated that the period of continuous fermentation should be controlled in 10 days for more lactic acid and less acetic acid. Compared with the untreated stalk, the crude protein content of the partially decomposed stalk mixed with the culture broth of SFC-2 increased by 36.17%. Twelve Nanyang cattles were used as experimental animal to determinate their feed intake on the treated straw, the results showed that the dry matter intake increased by 21.71%, compared to the untreated treatment. In conclusion, by coupling lignocellulose decomposition of corn stalk and malolactic fermentation of lactic acid bacteria, both digestibility and nutritive value of corn stalk and dry matter intake of beef cattle on it were improved.