Effects of different proportions of stevia stalk on nutrient utilization and rumen fermentation in ruminal fluid derived from sheep.

Abstract

<h4>Background</h4>Stevia straw is a byproduct of sugar crop stevia. It is a good feed material because of richness in nutrients and active substances (steviosides and flavonoids). However, due to improper utilization such as piling, burning and so on, it became a large amount of wasted straw resources and lead to environmental pollution.<h4>Methods</h4>We added 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0% and 1.5% of stevia stalk to study the effects of different stevia stalk concentrations on nutrient utilization and rumen fermentation in sheep (based on sheep diet). <i>In vitro</i> fermentation method was used, with 17 repetitions for each treatment. All fermentation substrate based on sheep diet with different stevia stalk concentrations were fermented for 2 h, 6 h, 12 h, 24 h and 48 h, then the gas production, dry matter degradability (DMD), crude protein degradability (CPD), neutral detergent fiber degradability (NDFD), acid detergent fiber degradability (ADFD), pH, ammonia nitrogen (NH₃-N) and volatile fatty acids (VFAs) were determined.<h4>Results</h4>The results showed that at different fermentation time, the change trend of gas production in each teatment was basically same, but the maximum occurred in 1.0% treatment at 48 h. The DMD, CPD, NDFD and ADFD of sheep diets increased with fermentation time increasing, especially the CPD_48h, NDFD_48h and ADFD_48h of diets in 0.8%, 1.0% and 1.5% treatments were significantly higher than those in control (<i>P</i> < 0.05). The pH of fermentation substrate in each treatment remained within the normal range of 6.21∼7.25. NH₃-N_24h-48hin 0.8%, 1.0% and 1.5% treatments were higher than that in control. At 6 h-12 h, the total acid content of 0.8% and 1.0% treatments were significantly higher than those of other treatments (<i>P</i> < 0.05), it reached the highest in 1.0% treatment. According to overall evaluation, effect ranking of stevia stalk on sheep nutrient utilization was as follows: 1.0% >0.8% >1.5% >0.4% >0.6% >0.2%. Overall, 1.0% stevia stalk could promote nutrient degradation and sheep rumen fermentation.