Sweet potato vines (SPV) nutrients can support livestock production, but the high moisture content makes them prone to deterioration after harvest. Ensiling, which preserves plant material through fermentation without air, offers a practical solution. How added bacteria influence both preservation and the transformation of plant material is essential for improving their feeding value.

A research team led by Prof. KONG Xiangfeng from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (CAS), collaborating with researcher from the Institute of Microbiology of CAS, found that fermentation with a mixture of lactic acid bacteria can improve the preservation and nutritional characteristics of SPV, and a moderate proportion of the fermented SPV can improve feed efficiency in pigs, highlighting its potential for converting agricultural byproducts into feed resources.

The study was recently published in Chemical Engineering Journal.

In the study, two bacterial species, Lactiplantibacillus plantarum and Pediococcus pentosaceus, were added and compared with naturally fermented SPV over eight weeks. Nutrient measurements, microscopy, and analyses of microbial DNA and small molecules were combined to track changes during fermentation.

The bacterial treatment consistently lowered pH and ethanol accumulation. At later stages, the treated vines contained higher crude protein concentration and less crude fiber than naturally fermented material. Microscopy also revealed greater disruption of plant tissues, suggesting that fermentation altered structural barriers that can restrict access to nutrients.

These changes coincided with a microbial community dominated by Lactiplantibacillus. In contrast, the predominant microorganisms varied more over time during natural fermentation. Further analyses identified associated changes in microbial genes and chemical profiles related to carbohydrate processing, amino acid metabolism, and vitamin-related pathways. Together, these observations connect improved fermentation performance with changes in plant structure and microbial activity.

To assess practical feeding value, the team conducted an eight-week trial involving 32 finishing Ningxiang pigs fed diets containing 0%, 4%, 8%, or 12% fermented SPV. At 4% inclusion, the feed-to-gain ratio fell from 4.98 to 4.21—approximately 15% less feed per unit of weight gain than in the control group.

Final body weight, average daily gain, and average daily feed intake did not differ significantly among diets. Higher inclusion levels provided no significant overall feed-to-gain advantage over the control, emphasizing the importance of an appropriate dietary proportion.

Dr. HU Weidong, The first author, emphasised these findings support controlled fermentation as a promising approach to utilizing SPV in livestock feeding. Larger trials and measurements of nutrient digestibility will help establish its broader applicability.

Contacted: KONG Xiangfeng

E-mail: nnkxf@isa.ac.cn

Figure 1. Lactic acid bacteria reshape microbial communities and metabolic processes during sweet potato vine fermentation and support its utilization as a feed resource for Ningxiang pigs. (Imaged by HU Weidong)