The effects of natamycin and hexanoic acid on the bacterial community, mycotoxins concentrations, fermentation profiles, and aerobic stability of high moisture whole-crop corn silage
Introduction
Whole-crop corn silage has become the predominant dietary ingredient in modern dairy and beef operations worldwide because of its high-net energy and physically effective neutral detergent fiber (NDF) for dairy rations. The high starch and energy in whole-crop corn silage make it also ideal for finishing cattle. The promotion of the project “Changing grain to forage” in China enhanced the planting of whole-crop corn for silage over the last 10 years.
Although whole-crop corn is a readily fermentable crop for silage production, corn silage from hot or tropical regions is usually poorer in quality than that produced in cool or temperate climates (Bernardes et al., 2018). The high temperature accompanied humidity favor the propagation of bacterial and fungal pathogens such as Escherichia coli, Penicillium spp., Aspergillus spp., and Fusarium spp. (Samapundo et al., 2005). Several species belonging to these fungal genera can produce mycotoxins, resulting in the accumulation of mycotoxins in human and livestock food chains (Ogunade et al., 2018).
Mitigating the risk of mycotoxins and improving the hygienic quality of silage during ensiling and feed-out require additives with capacity to inhibit undesirable bacteria and prevent toxin contamination (Mugabe et al., 2019). Hexanoic acid is a potential additive to inhibit the growth of yeasts and molds in silages because of its high dissociation constants (pKa). Natamycin is a pimaricin fungicide permitted by over 150 countries and has been used in human food such as fermented dairy products, meats, beverages, fruits, and vegetables (Aparicio et al., 2016). Both hexanoic acid and natamycin showed antifungal properties, however, whether they had the anti-bacterial capacity and affected the fermentation process and succession of bacterial community during ensiling are still unclear. Lactobacillus plantarum is one of commercial starters employed in silage fermentation, however, it usually reduces the bunk life and worsens the aerobic stability in corn silages since sufficient LA provide substrates for the development of yeasts and subsequent spoilage during aerobic exposure (Ma et al., 2017). Romero et al. (2018) reported that inoculants improved low-moisture whole-crop corn silage quality because of a shift in the bacterial and fungal community composition during ensiling. To our knowledge, no study has investigated the efficacy of hexanoic acid and natamycin on bacterial community and fermentation and hygienic quality of silage. We hypothesized that both hexanoic acid and natamycin showed antifungal properties rather than anti-bacterial capacity, and they could alter the succession of bacterial community to improve the fermentation and hygienic quality as well as L. plantarum.
Thus, this study aimed to examine the effects of natamycin, hexanoic acid, and L. plantarum on fermentation characteristics, aerobic stability, mycotoxins concentrations, and bacterial community of whole-crop corn silage.
Section snippets
Silage preparation and treatments
Whole-crop corn was planted in the experimental field of Nanjing Agricultural University (32.04° N, 118.88° E), which contained 5 plots (about 200 m2/plot). The region is characterized by subtropical monsoon climate with mean annual precipitation of 1106 mm and average temperatures of 15.4 ºC. On November 17, 2017, 3 plots of whole-crop corn at 1/2 milk lines stage were randomly selected and manually harvested. Then the whole-crop corn was chopped into 2–3 cm length using a forage cutter
Results
The DM and WSC concentrations of fresh whole-crop corn were 219 g/kg FW and 186 g/kg DM, respectively. The population of yeast and molds, and LAB was 2.27 and 6.16 log10 cfu/g FW, respectively.
Discussion
All silages pH decreased below 4.0 within 14 d, which partly be attributed to the lower DM contents (21.9%) than recommended range of DM concentration (32–35%) (Romero et al., 2018). Queiroz et al. (2018) reported that the low DM in the silages contributed to the high fermentation rates and rapid silage pH decline.
Conclusion
HEX depressed LA accumulation and resulted in higher pH and WSC than other silages during the initial 7 d of ensiling, however, it extended to the aerobic stability over 144 h. The addition of NAT or LP improved the fermentation quality of whole-crop corn silage by enhancing the proliferation of Lactobacillus. Lactobacillus genera colonized and dominated the LP and NAT silages. The LP and NAT silages had lower mycotoxins concentrations than fresh corn, CON, and HEX silages after 60 d of
CRediT authorship contribution statement
Xianjun Yuan and Tao Shao: designed the experiment. Xianjun Yuan, Xin Yang, and Wenbo Wang: performed the experiment, analysis, and writing. Junfeng Li, Zhihao Dong, and Jie Zhao: performed the editing and revision. All authors have read and agreed to the published version of the manuscript.
Declaration of Competing Interest
The authors declare that there are no conflicts of interest.
Acknowledgements
This work was partially supported by the National Natural Science Foundation of China (31872421) and the National Key Research and Development Program of China (2017YFE0104300).
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