Effect of varying levels of stevioside supplementation on in vitro gas production and rumen fermentation in sheep

We studied the effect of varying supplemental dietary stevioside levels on nutrient degradation and rumen fermentation in sheep. In this study, eight experimental sheep treatments were set up, with stevioside supplements at 0 (CK group), 0.01%, 0.04%, 0.07%, 0.10%, 0.15%, 0.20%, and 0.30% (based on the air-dried matter in the diet), and the rumen fermentation and nutrient degradation rates were evaluated for 48 h by an in vitro gas production method. The results showed that the gas production (GP), dry matter degradation rate (DMD), volatile fatty acid, and methane yields, in all treatments, increased with prolonged rumen degradation time, peaking at 48 h. However, pH decreased with prolonged rumen degradation time. After 12 h, the GP of the 0.10% group showed a significant increase compared to the CK group (P < 0.05). At 24 h, the DMD in the 0.20% and 0.30% groups was significantly lower than in the CK group (P < 0.05), with reductions of 9.71% and 5.80% (P < 0.05), respectively. Compared with the CK group, there were no significant differences in DMD and crude protein degradation rate of all other groups at 48 h (P > 0.05). With an increase in fermentation time, the content of ammonium nitrogen (NH₃-N) in the rumen fluid of each treatment ranged from 7.05～13.97 mg·dL⁻¹, which was within the appropriate concentration range for rumen microbial activity. The 0.07% and 0.10% groups maintained elevated levels of acetic acid and total volatile fatty acids. In conclusion, the optimal concentration range of stevioside in sheep diet was observed to be 0.07%～ 0.10%. These results provide a theoretical basis for adopting the appropriate stevioside supplementation levels in sheep production practices.