Detoxification and fermentation of fresh cassava roots using sulfur and cyanide-utilizing bacteria for FTMR: An <i>in vitro</i> study

This study aimed to evaluate the effects of sulfur and cyanide-utilizing bacteria (CUB) supplementation, along with varying fermentation durations, on the nutritional quality, gas production kinetics, digestibility, and ruminal fermentation characteristics of fermented total mixed rations (FTMR) based on fresh cassava tubers. A completely randomized design (CRD) was applied in a 3 × 3 factorial arrangement consisting of three additive treatments (no additive, 1.5% sulfur, and CUB at 108 CFU/g) and three fermentation periods (0, 7, and 14 days), resulting in nine dietary treatments. The CUB strain used was Enterococcus faecium KKU-BF7, previously isolated from rumen fluid for its cyanide-degrading capability. Results revealed that both additives and fermentation time significantly (p < 0.01) affected feed chemical composition, particularly crude protein (CP), either extract (EE), acid detergent fiber (ADF), and acid detergent lignin (ADL). The highest NH3-N concentration (22.43 mg/dL; p < 0.01) was observed in the CUB group fermented for 14 days. In vitro dry matter digestibility (IVDMD) was highest in the CUB group, similar to the control, while sulfur reduced it (p < 0.01). In vitro organic matter digestibility (IVOMD) is highest on day 14 of fermentation, regardless of additive (p < 0.05). Sulfur supplementation, particularly after 14 days of fermentation, markedly reduced cumulative gas production over the 96-hour incubation period. As the fermentation time increased, acetate decreased, while propionate and butyrate increased. At the onset of fermentation (day 0), HCN concentrations were similar among treatments (≈81–83 ppm). After 7 days, CUB reduced HCN to 11.9 ppm, compared with 29.0 ppm for sulfur and 46.51 ppm for the control (p < 0.01). By day 14, HCN in the CUB group further declined to 4.12 ppm, the lowest among treatments, compared with 10.11 ppm for sulfur and 22.77 ppm for the control (p < 0.01). These findings demonstrate that CUB is a promising additive for improving cassava-based FTMR through enhanced detoxification, fermentation efficiency, and nutrient utilization. Optimization of additive type and fermentation duration can significantly enhance feed safety and energy availability in ruminant diets.