| In addition to the reduction in water soluble carbohydrates (WSC) content during ensiling, losses of starch and hemicellulose are also observed in silages. It is expected that the starch and hemicellulose can be degraded into some simple carbohydrates by plant and microbial enzymes under the acidic conditions. To date, however, little information is available about total mixed ration (TMR) silage, particularly regarding the extents and causes of starch and hemicellulose degradation in TMR silage during ensiling. Excessive consumption of carbohydrates such as starch and hemicellulose during ensiling can result in negative impacts on nutrition and feeding value of TMR silage. Thus, it is important to have a better understanding of the dynamics and mechanisms underlying the starch and hemicellulose loss with prolonged ensiling of TMR silage. The main contents and conclusions are as follows:1. In experiment 1, whole crop corn and TMR formulated mainly with whole crop corn and other agricultural and food by-products were used to clarify the fermentation quality, microbial and carbohydrate components dynamics during fermentation. The WSC, starch and hemicellulose contents significantly declined with prolonged ensiling of whole crop corn silage. Similar results were also observed in TMR silage with a decrease in starch and hemicellulose concentrations during fermentation.2. In experiment 2, TMRs were adjusted to different moisture content (375g/kg,432g/kg and 483g/kg) and used for investigating the effects of moisture content on carbohydrate components dynamics in TMR silages. Irrespective of moisture content, the starch and hemicellulose contents decreased as ensiling advanced. TMR silages with high moisture content (483g/kg) exhibited highest reduction of starch and hemicellulose than that in the other two TMR silages. Therefore, the loss of starch and hemicellulose can be inhibited to some extent by reducing the moisture content in TMR silages.3. To reveal the dynamics and mechanisms underlying the starch and hemicellulose loss with prolonged ensiling of TMR silage, TMR formulated mainly with soybean curd residue and two different roughages of alfalfa hay (ATMR) and Leymus chinensis hay (LTMR) were subjected to a series time of fermentation in experiment 3. The loss of carbohydrates, microbial enzyme activities, succession of dominant amylolytic or hemicellulolytic microbes during ensiling as well as the microbial and enzymatic properties were investigated to clarify the main enzyme producing microbes and the roles of their enzymes in starch and hemicellulose degradation during fermentation of TMR silages. Results indicated as follows:(1) In addition to the substantial loss of water soluble carbohydrates, loss of starch and hemicellulose was also observed in both ATMR and LTMR silages with prolonged ensiling. Higher loss of starch, but lower hemicellulose loss was observed in ATMR silage compared to LTMR silage.(2) The microbial amylase contributes to starch hydrolysis during the ensiling process in both ATMR and LTMR silages, whereas the microbial hemicellulase participates in the hemicellulose degradation only at the early stage of ensiling. The high concentrations of lactic and acetic acids produced during ensiling could lead to the continued loss of hemicellulose after 14 d of fermentation in both ATMR and LTMR silages.(3) During the early stage of fermentation, the main amylase-producing microbes were Bacillus amyloliquefaciens, B. cereus, B. licheniformis, and B. subtilis in ATMR silage and B. flexus, B. licheniformis, and Paenibacillus xylanexedens in LTMR silage, whereas Enterococcus faecium was closely associated with starch hydrolysis at the later stage of fermentation in both TMR silages.(4) B. amyloliquefaciens, B. licheniformis, and B. subtilis and B. licheniformis, B. pumilus, and P. xylanexedens were the main source of microbial hemicellulase during the early stage of fermentation in ATMR and LTMR silages, respectively. |
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