Abstract
The influence of mixing alfalfa with whole-plant corn in different proportions on the fermentation characteristics and bacterial community of silage was investigated. Alfalfa and whole-plant corn, harvested at dry matter content of 276.47 and 328.43 g/kg fresh weight, accordingly, were chopped to approximately 2 cm and mixed at ratios of 100:0 (C0, control), 80:20 (C20), 60:40 (C40), 40:60 (C60), 20:80 (C80) and 0:100 (C100) on a fresh weight basis, respectively. Silos of each treatment were produced in triplicate and anaerobically fermented in darkness for 100 days at room temperature (20–21 °C). At silo opening, silage fermentation characteristics and bacterial composition and diversity were analyzed. The C0 silage was weakly preserved, evidenced by a low lactic acid concentration and a high value of pH, acetic acid, propionic acid, butyric acid and ammonia nitrogen. With corn proportion in the mixture increasing from 0% to 40%, silage pH, acetic acid, butyric acid and ammonia nitrogen level decreased, whereas the value of lactic acid and lactic acid to acetic acid ratio increased. The C40, C60, C80 and C100 silages’ Flieg score, used to evaluate the overall fermentation quality, was above 80 and higher than C0 (25) and C20 (61) silages. The C0 silage contained a complex bacterial community at the genus level, consisting mainly of Enterococcus (38.86%), Enterobacteria (20.61%), Rhizobium (8.45%), Lactobacillus (8.15%), Methylobacterium (5.54%) and Weissella (5.24%). As corn percentage increased from 0% to 40%, the relative abundance of desirable Lactobacillus increased and undesirable Rhizobium and Methylobacterium population reduced. With corn proportion in the mixture increasing from 0% to 40%, inclusion of corn to alfalfa at ensiling significantly improved silage fermentation quality and shifted the bacterial community for better silage preservation. Overall, high quality silage was produced when alfalfa was combined with at least 40% whole-plant corn on a fresh weight basis.
Highlights
Alfalfa (Medicago sativa L.) has been planted widely in northern China and many other regions of the world due to its high content in many essential vitamins, minerals and protein [1,2]
It is challenging to directly ensile alfalfa principally owing to a high buffering capacity (BC) [4,5] and a low water-soluble carbohydrates (WSC) and dry matter (DM) concentration [5,6]
We previously evaluated the bacterial composition and diversity of silage prepared with alfalfa, corn stalk and their mixture by Illumina MiSeq sequencing, after 65 days (d) of ensiling, and found that the relative abundance of desirable Lactobacillus increased, whereas undesirable Enterobacter abundance decreased as corn stalk percentage ranged from 0% to 60% [5]
Summary
Alfalfa (Medicago sativa L.) has been planted widely in northern China and many other regions of the world due to its high content in many essential vitamins, minerals and protein [1,2]. Improved characterizing silage microbiota has been achieved through molecular technologies, including denaturing gradient gel electrophoresis [12], random amplified polymorphic DNA [13] and terminal restriction fragment length polymorphism [14]. These approaches only identify some of the operational taxonomic units (OTUs) present due to poor detection limits [15]. We previously evaluated the bacterial composition and diversity of silage prepared with alfalfa, corn stalk and their mixture by Illumina MiSeq sequencing, after 65 days (d) of ensiling, and found that the relative abundance of desirable Lactobacillus increased, whereas undesirable Enterobacter abundance decreased as corn stalk percentage ranged from 0% to 60% [5]. To the best of our knowledge, most of the studies on co-ensiling alfalfa and corn focus on silage fermentation parameters and chemical characteristics, and very few works have evaluated the bacterial community in alfalfa-corn mixture silage
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