Influence of Trace Elements Mixture on Bacterial Diversity and Fermentation Characteristics of Liquid Diet Fermented with Probiotics under Air-Tight Condition

Cu(2+), Zn(2+), Fe(2+) and I(−) are often supplemented to the diet of suckling and early weaning piglets, but little information is available regarding the effects of different Cu(2+), Zn(2+), Fe(2+) and I(−) mixtures on bacteria growth, diversity and fermentation characteristics of fermented liquid diet for piglets. Pyrosequencing was performed to investigate the effect of Cu(2+), Zn(2+), Fe(2+) and I(−) mixtures on the diversity, growth and fermentation characteristics of bacteria in the liquid diet fermented with Bacillus subtilis and Enterococcus faecalis under air-tight condition. Results showed that the mixtures of Cu(2+), Zn(2+), Fe(2+) and I(−) at different concentrations promoted Bacillus growth, increased bacterial diversity and lactic acid production and lowered pH to about 5. The importance of Cu(2+), Zn(2+), Fe(2+) and I(−) is different for Bacillus growth with the order Zn(2+)> Fe(2+)>Cu(2+)> I(−) in a 21-d fermentation and Cu(2+)>I(−)>Fe(2+)>Zn(2+) in a 42-d fermentation. Cu(2+), Zn(2+), Fe(2+) and I(−) is recommended at a level of 150, 60, 150 and 0.6 mg/kg respectively for the production of fermented liquid diet with Bacillus subtilis. The findings improve our understanding of the influence of trace elements on liquid diet fermentation with probiotics and support the proper use of trace elements in the production of fermented liquid diet for piglets.