Effects Of Four Functional Native Herbages In Alpine Meadow On Digestive Metabolism And Rumen Microecology Of Tibetan Sheep

Functional native herbage（FNH）accounts for 20%-30%of grassland biomass and more than 50%of grassland species richness.Like traditional herbage,FNH is an important component of terrestrial ecosystem productivity and biodiversity.The few studies on FNH have focused on its ecological functions,while the potential effects of the whole plant on digestion and metabolism and productivity of livestock remain to be elucidated.This study analyzed the effects of four FNH species in alpine meadows on growth performance,nutrient apparent digestibility,serum biochemical and antioxidant indices,rumen fermentation parameters and rumen microbial community of grazing Tibetan sheep based on the Maqu Grassland Agricultural Experiment Station of Lanzhou University.The main results are as follows:1.Effects of Ligularia virgaurea（LV）on digestion and metabolism of Tibetan sheepThe biomass of LV,which belongs to the Asteraceae family,accounts for 5%-20%of the total biomass of alpine meadows.In summer and winter,32 yearling Tibetan sheep were selected and randomly divided into 4 groups.Sheep were fed a basal diet with 0,100,200,or 300 mg/kg BW of LV per animal/d.In summer,100 and 200 mg/kg LV additions increased sheep average daily gain（ADG）by 9.6%and 19.8%and dry matter intake（DMI）by 4.1%and 6.4%,respectively（P<0.05）;and increased DMI by3.9%and 6.8%in winter（P<0.05）.At 200 mg/kg BW addition,digestible nitrogen（DN）,deposited nitrogen（RN）,digestible energy（DE）and metabolizable energy（ME）increased by 20.6%,48.4%,29.1%and 34.4%（P<0.05）,respectively;and 46.3%,18.9%and 25.3%（P<0.05）in winter for DN,DE and ME,respectively.LV increased superoxide dismutase（SOD）and glutathione peroxidase（GSH-Px）contents by 6.1-36.4%and 5.3-24.0%,respectively（P<0.05）.Total volatile fatty acid（TVFA）were elevated by 12.2%-14.7%（P<0.05）.In winter,bacteria associated with fiber catabolism,propionate production and energy utilization were elevated in the LV supplemental groups（P<0.05）.LV intake above 200 mg/kg reduced DMI and digestive metabolic efficiency.2.Effects of Stellera chamaejasme（SC）on digestion and metabolism of Tibetan sheepThe biomass of SC,which belongs to the Thymelaeaceae family,accounts for 3%-10%of the total biomass of alpine meadows.In summer and winter,32 yearling Tibetan sheep were selected and randomly divided into 4 groups.Sheep were fed a basal diet with 0,100,200,or 300 mg/kg BW of SC per animal/d.In summer,ADG and DMI increased by 16.7%and 5.3%（P<0.05）in the 100 and 200 mg/kg addition groups,respectively;in winter,DMI increased by 4.2%（P<0.05）.In summer,DN,RN and DE increased by 11.0%,34.1%and 3.8%,respectively,in the 100 mg/kg addition group（P<0.05）;in winter,DN increased by 10.2%-12.3%in the SC addition groups（P<0.05）.In summer,SC increased SOD and GSH-Px levels by 5.5%-8.2%and 6.9%-18.2%,respectively（P<0.05）;while rumen NH₃-N concentration decreased by 11.5%-42.6%.In winter,at 100 mg/kg addition,propionate concentration increased by 29.2%（P<0.05）.In summer,the conditional pathogenic bacteria,Selenomonas and Olsenella decreased in the SC supplemental groups,while the relative abundance of Firmicutes and Verrucomicrobiota increased（P<0.05）.In winter,the relative abundances of Bacteroides,Synergistota,Verrucomicrobiota and Cyanobacteria were increased in SC supplementation groups（P<0.05）.The efficiency of digestion and metabolism in Tibetan sheep was strongly influenced by the main rumen bacterial genera,and SC promoted digestive and metabolic efficiency and productivity in grazing Tibetan sheep at the level of 100 mg/kg addition.3.Effects of Pedicularis kansuensis（PK）on digestion and metabolism of Tibetan sheepThe biomass of PK,which belongs to the Scrophulariaceae family,accounts for5%-18%of the total biomass of alpine meadows.In summer and winter,32 yearling Tibetan sheep were selected and randomly divided into 4 groups.Sheep were fed a basal diet with 0,100,200,or 300 mg/kg BW of PK per animal/d.In summer,the DMI increased by 4.5%at 300 mg/kg addition group;in winter,the OM digestibility increased by 6.2%at 200 mg/kg addition group（P<0.05）.In winter,PK increased serum SOD and GSH-Px levels by 1.8%-6.9%and 1.9%-6.7%,respectively（P<0.05）.In summer,PK increased ruminal NH₃-N and isobutyrate concentrations by 3.0%-19.5%and 12.4%-46.2%,respectively;in winter,NH₃-N concentrations were increased by4.3%-15.9%（P<0.05）.In summer,the relative abundance of Firmicutes,Bacteroidetes and some Prevotellaceae members increased in PK supplemental groups（P<0.05）.In winter,Patescibacteria,Rikenellaceae＿RC9＿gut＿group and Prevotellaceae＿UCG＿001were increased in PK supplementation groups（P<0.05）.At the level of 200 mg/kg addition,SC promotes digestive and metabolic efficiency in grazing Tibetan sheep.4.Dynamic adaptation of the rumen microbiome to Anemone rivularis（AR）in grazing Tibetan sheepThe biomass of AR,which belongs to the Ranunculaceae family,accounts for 6%-15%of the total biomass of alpine meadows.32 yearling Tibetan sheep were selected and randomly divided into 4 groups.Sheep were fed a basal diet with 0,100,200,or300 mg/kg BW of AR per animal/d.Rumen fluid was collected from Tibetan sheep in each treatment group at the pre-trial period（Day 0）,the mid-trial（Day 14）and the end-trial period（Day 30）of the experiment to analyze the dynamic changes of rumen microbiota.Ruminal bacterial diversity tended to increase and then decrease throughout the test period,while ruminal fungal diversity tended to decrease（P<0.05）.The relative abundance of Prevotella increased over time regardless of AR addition level,while the relative abundance of unclassified＿F082 and Butyrivibrio decreased（P<0.05）.Ruminal fungi were more sensitive to the addition of AR to the diet compared to rumen bacteria.Due to the higher stability and functional redundancy of the rumen microbiota,there will be a gradual synergistic adaptation to the intake of AR over time.The dose of FNH intake affected the feeding feedback pathway of Tibetan sheep,mainly in terms of changes in feed intake,and there was a threshold effect on the effect of FNH on the digestive metabolism of Tibetan sheep.At appropriate intake doses,DMI,ADG,nutrient digestibility,nitrogen and energy metabolism efficiency,serum antioxidant performance and rumen fermentation characteristics were significantly improved in grazing Tibetan sheep.Among them,the appropriate doses of LV and PK for grazing Tibetan sheep were 200 mg/kg BW and 100 mg/kg BW for SC;however,correction is needed to determine the optimum additive amount in livestock grazing production system.There is a synergistic effect between the function of rumen microorganisms and the digestion and metabolism of nutrients in ruminant,and there is a specific adaptive response of the rumen microbiome to the intake of FNH.In conclusion,for the characteristics of different FNH and utilized at reasonable doses,FNH can improve the productivity of Tibetan sheep,alleviate grass-livestock conflicts,and help promote the sustainable development of alpine meadow grazing production system.Subsequent studies need to further focus on FNH product development and application,as well as the elimination measures and technology development for the adverse effects of some types of FNH on livestock.