Fermentation Parameters, Amino Acids Profile, Biogenic Amines Formation, and Bacterial Community of Ensiled Stylo Treated with Formic Acid or Sugar

Substantial proteolysis occurs and free amino acids can be degraded to biogenic amines by decarboxylation during stylo (<i>Stylosanthes guianensis</i>) ensiling. High biogenic amine concentrations in silage are harmful to the health of ruminant animals. The purposes of this work were to (1) analyze the biogenic amines and amino acids concentrations, bacterial composition, and fermentation profile of spontaneously fermented stylo silage, (2) explore the effect of formic acid or sugar additive on these silage parameters, and (3) further reveal the correlations between silage amines and fermentation parameters, amino acids, and bacteria. Freshly chopped stylo was treated with distilled water (control), formic acid (4 mL/kg), and sugar (20 g/kg) and fermented for 28 days. The results indicated that putrescine (321 mg/kg dry matter), cadaverine (384 mg/kg dry matter), and tyramine (127 mg/kg dry matter) rapidly increased in concentration and become predominant in the control silage after 28 days of fermentation. Applying formic acid and sugar at ensiling, especially the acidifier, significantly decreased putrescine, cadaverine, tyramine, and total biogenic amine concentrations compared with the control treatment (<i>p</i> < 0.0001). <i>Clostridium pabulibutyricum</i>, <i>Weissella cibaria</i> and <i>W. paramesenteroides</i> were the predominant bacteria in the control silage, and the application of both additives remarkably lowered their relative abundance in comparison with the control treatment (<i>p</i> < 0.001). Correlation analysis showed that putrescine, cadaverine, and tyramine were positively related to pH, butyric acid, non-protein nitrogen, and ammonia nitrogen (<i>p</i> < 0.01). These amines also had significant correlations with <i>C. pabulibutyricum</i>, <i>W. cibaria</i> and <i>W. paramesenteroides</i> (<i>p</i> < 0.001). Putrescine, cadaverine, and tyramine were the main biogenic amines and <i>C. pabulibutyricum</i> was the predominant undesirable bacterium in naturally fermented stylo silage. <i>C. pabulibutyricum</i>, <i>W. cibaria</i> and <i>W. paramesenteroides</i> were positively related to putrescine, cadaverine, and tyramine formation. The application of formic acid or sugar significantly reduced the undesirable bacterial population and improved the fermentation and hygienic quality of the stylo silage. These findings lay the foundation for further elucidating the microbial mechanism underlying the main biogenic amine formation during fermentation of stylo silage.