Feed value of native forages of the Tibetan Plateau of China

The nutritive value of 22 native forages consisting of sedge, grass, forb and shrub species harvested in August, September and October from the Tibetan Plateau of China was assessed by using chemical, in sacco degradability and in vitro gas production analyses. Generally, data from the study showed that metabolizable energy value (ME) as estimated by in vitro gas production and chemical composition data decreased with maturity. Forb forages had the highest ME value (9.18 MJ/kg) and grasses the lowest (8.74 MJ/kg). ME value of grasses showed a sharp decrease from August to September, then it remained constant. Other forages showed a linear decrease of ME value with maturity. The relative decrease in the content of nitrogen available for microbial degradation (degradable N g/kg DOM) with maturity was similar for sedge, grass and forb species. Grazing of sedges and forbs in mixed communities of grasses may be important for supplying extra nitrogen for microbial fermentation and increasing efficiency of utilisation of grasses. Data from in vitro gas production completed in presence of polyethylene-glycol 4000 (PEG), a phenolic-related binding agent, showed that some species of sedges, forbs and shrub might contain large amounts of inhibitory compounds to rumen microbes. Further in vivo studies are needed to establish optimum levels of inclusion of such plants in Yak diets to optimise grassland use and animal performance. Finally, data from grasses suggested that such forages should preferably be grazed by August while their nutritive value was high.