Effects Of Shrub Encroachment On Grazing Behavior,Rumen Fermentation And Serum Parameters Of Yaks In Alpine Meadows

Shrub encroachment in grassland is one of the most remarkable changes over the past 150 years.The Qinghai–Tibetan Plateau（QTP）is the largest grassland ecosystem and plays a vital role in livestock production.However,little information is available concerning the effect of shrub encroachment on livestock productivity on the QTP.In the present study,the alpine meadow was used to investigate the effect of shrub encroachment on grazing yak production during the different forage maturation stages.The shrub coverage（Control,no shrub;Low,5.4%shrub coverage;Middle,11.3%shrub coverage;High,20.1%shrub coverage）in the pastures was defined and selected as the experimental pastures.In the present study,the chemical composition and biomass of forage were measured to illuminate the effect of shrub encroachment on forage productivity.Afterwards,the effects of the shrub coverage on grazing behavior,rumen bacterial diversity,rumen fermentation,serum nutrient metabolism parameters and health indices,and economic benefit of yaks were evaluated by grazing yaks trial to illuminate the influence of shrub encroachment in alpine meadows on productivity of yaks grazing system on the QTP.The objectives of the study were to investigate the response mechanism of grazing livestock to shrub encroachment into the pastures.The results derived from the present study as following:1)Although there was not significant difference between shrub coverage treatments（0 to 20%）for forage chemical composition（P<0.05）,high shrub coverage group（20.1%）decreased the productions of dry matter（DM,P=0.012）,crude protein（CP,P=0.012）,neutral detergent fiber（NDF,P=0.022）and acid detergent fiber（ADF,P=0.041）compared with control group.The concentrations of DM,CP,and organic matter of forage significantly decreased with the forage maturation（P<0.001）,whereas the concentrations of NDF and ADF increased（P<0.001）,as a result reduced the efficiencies of nutrition digestibility and energy utilization（P<0.001）.Among which,the relationships(r_linear=0.422 to 0.778;r_quadratic=0.568 to 0.815)were obtained between forage CP concentration and nutrition digestibility or energy parameters（P≤0.003）,and the CP digestibility does not increase when forage CP concentration over the value of 9.7%.2)The diurnal behavioral patterns were similar for the yaks grazing in pastures with different levels of shrub coverage,and yaks spent average 76.5%,14.7%and 8.8%of the time for grazing,ruminating/resting and walking,respectively.An increasing shrub coverage enhanced the time yaks allocated to walking（P=0.029）,bites per minute（P=0.036）and steps per minute（P=0.029）,whereas decreased the time allocated to ruminating/resting（P=0.045）.3)Bacteroidetes and Firmicutes as the two dominant phyla of yak rumen fluid were identified across all the samples and represented 45.0%and 44.4%of the total sequences,respectively,when the yaks were grazed on the alpine meadows.The other high relative abundances of bacterial phylum were Spirochaetes,Proteobacteria,SR 1（Absconditabacteria）etc.4)Although the concentrations of ammoniacal nitrogen and volatile fatty acids in rumen significantly increased（P<0.05）with an increase in shrub coverage,the microbial protein content and fermentative mode were not influence by shrub coverage（P>0.05）.Compared with senescent stage,yaks in the bloom stage have higher concentrations of ammoniacal nitrogen（P=0.032）,volatile fatty acids（P=0.002）and microbial protein（P<0.001）in rumen,indicating that yaks grazing in forage bloom stage improved the efficiencies of energy and nitrogen utilization.The relative abundances of Ruminococcus 1,Ruminococcaceae NK4A214 group,Fibrobacter,Erysipelotrichaceae UCG-004,probable genus 10,Prevotella 1,Prevotellaceae UCG-001 and Selenomonas 1 used for degrading cellulose or hemicellulose were positive correlation with acetate concentration,while the relative abundances of Ruminococcaceae NK4A214 group,Ruminococcaceae UCG-010,Christensenellaceae R-7 group and Prevotellaceae UCG-003 were in favor of increase the contents of propionate and butyrate in rumen.5)Although there was not significant difference between shrub coverage treatments for serum biochemical parameters（P<0.05）of yaks,serum concentrations of glucose（P=0.037）,β-hydroxybutyric acid（P<0.001）and blood urea nitrogen（P=0.001）significantly decreased with forage maturation,because of the deficiency of the nutrition in forage.Additionally,a higher non-esterified fatty acid concentration（P<0.001）was found for yaks grazing in winter due to mobilization of fat to provide energy,consequently,potentially damaged to animal health.6)Yaks grazed on the pastures with high shrub coverage（20.1%）decreased economic benefit by 19%compared with control group（P=0.041）,indicating that shrub encroachment into alpine meadows on the QTP need a certain level of control for the sustainable grazing yak production.The results derived from the present study provide more information for the influences of shrub encroachment on productivity of grazing livestock and an insight for the sustainable utilization of pastures with shrub encroached.