| Astragalus variabilis is a perennial herbaceous plant belonging to the genus Astragalus in the Fabaceae family.It is one of the main poisonous weeds in the natural grasslands of northwest China.On the one hand,due to overgrazing,ecological degradation has led to the proliferation of toxic plants such as A.variabilis,while the types and quantity of edible forage have decreased.This has forced grazing livestock to consume toxic plants,resulting in poisoning and even death,seriously affecting the healthy development of grassland animal husbandry and requiring prevention and control measures.On the other hand,previous studies have shown that A.variabilis has high nutritional value,strong stress resistance,and potential medicinal value.In some grazing areas where there is a shortage of drought-resistant forage if A.variabilis can be controlled and added to the diet or detoxified before feeding,it can turn waste into treasure and has great potential for utilization.However,in the past,the understanding of the distribution of A.variabilis in suitable habitats was limited by manual field investigations,which hindered its prevention and control,and resource utilization.In addition,there have been no studies reporting the safety threshold and feeding effects of adding A.variabilis to animal feed.Therefore,this study focuses on the prevention and control,and resource utilization of A.variabilis,including(1)using geographic information software ArcGis and MaxEnt ecological niche model based on R optimization to explore the distribution of suitable habitats for current and future A.variabilis and the relationship between habitat suitability and livestock poisoning;(2)conducting toxicological safety evaluation of A.variabilis hay powder added to mice feed at doses of 0,5%,10%,15%,and30% by observing clinical symptoms,detecting blood physiological and biochemical indicators,and pathological tissue sections;(3)exploring the feeding effect of adding A.variabilis to animal feed by detecting related immune factors(IL-1β,IL-6,IL-2,and IgG)and antioxidant indicators(SOD,MDA,and GSH-PX)in the serum of animals in each dose group,as well as calculating the feed-to-weight ratio.The study obtained the following results:1.Simulation and prediction of the distribution of A.variabilis suitable habitats under current and climate background: After selecting 189 distribution points and 10 environmental factors data with a spatial filtering scale of 10 km,the model was built.The optimal parameters were set as "FC=H,RM=0.5".AUC,TSS,CBI,and OR10 indicators showed that the modeling performance was robust and reliable.Jackknife analysis results indicated that the February average maximum temperature,June average precipitation,and surface soil organic carbon were the important environmental variables that affect the distribution of A.variabilis.The results of the environmental response curve were consistent with the characteristics of cold resistance of A.variabilis,drought resistance,and tolerance to poor soil.Under current climate conditions,the suitable habitats of A.variabilis are mainly distributed in western Inner Mongolia,northern Gansu,central and northeastern Xinjiang,and other regions.Correlation analysis results showed that habitat suitability was positively correlated with the frequency of livestock poisoning.Under four SSP climate scenarios in the future,the suitable habitats of A.variabilis will shift towards higher latitudes and elevations.2.Determining the safety threshold for the use of A.variabilis in animal feed:Observations of clinical symptoms showed that mice in the 30% dose group exhibited severe poisoning symptoms,mice in the 15% dose group exhibited mild poisoning symptoms,and mice in the 10% and 5% dose groups showed no difference compared to the control group.Results of an open field test showed that mice in the 30% dose group had a significantly reduced number of movements per minute compared to the control group.Results of blood physiological index tests showed that RBC,HGB,HCT,and PLT were significantly decreased in the 30% dose group;RBC,HGB,HCT,and PLT were significantly decreased in the 15%dose group;and RBC,HGB,and PLT were significantly decreased in the 10% dose group.Results of blood serum biochemical index tests showed that ALT,AST,and CRE were significantly increased and TP and ALB were significantly decreased in the 30% dose group;AST was significantly increased and TP,ALP,and ALB were significantly decreased in the15% dose group;AST was significantly increased and ALB was significantly decreased in the10% dose group;and AST was significantly increased in the 5% dose group.Results of tissue slice observations showed that mice in the 30% dose group had vacuolar degeneration in the heart,liver,kidney,and cerebellum,cytoplasmic shrinkage,and disappearance of nuclear nucleoli in brain nerve cells;mice in the 15% dose group had vacuolar degeneration in the kidney and mild hepatocyte swelling;mice in the 10% dose group had vacuolar degeneration in the kidney;and mice in the 5% dose group showed no pathological changes in any organs.3.Evaluation of the effects of A.variabilis supplementation: Results of growth performance evaluation showed that the 5% dosage group had a slight improvement in daily weight gain and a slight decrease in the feed-to-gain ratio;the daily weight gain and the feed-to-gain ratio of the 10% dosage group were similar to those of the control group;the daily weight gain of the 15% dosage group was significantly reduced,and the feed-to-gain ratio slightly increased;the daily weight gain of the 30% dosage group was significantly reduced,and the feed-to-gain ratio significantly increased.Results of antioxidant capacity evaluation showed that the 5% dosage group had a slight increase in SOD and GSH-PX and a slight decrease in MDA;the 10% dosage group had a slight increase in SOD,a significant increase in GSH-PX,and a slight decrease in MDA;the 15% dosage group had a significant increase in SOD and GSH-PX and a slight decrease in MDA;the 30% dosage group had a significant increase in SOD,GSH-PX,and MDA.Results of immune function evaluation showed that the 5% and 10% dosage groups had a slight increase in IL-2 and IL-6;the 15%and 30% dosage groups had a significant increase in IL-2 and IL-6.Conclusion: Currently,the distribution of A.variabilis,which is mainly related to livestock poisoning,is mainly concentrated in western Inner Mongolia,northern Gansu,central and northeastern Xinjiang,and other regions.The habitat suitability of A.variabilis is related to livestock poisoning.In the future,the predicted A.variabilis suitable habitat will shift to higher altitude and latitude regions.The safe threshold for A.variabilis feed additives is between 5% to 10%.When used within the safe dosage range,the growth performance,antioxidant capacity,and immune function of mice can be improved,but the differences are not significant.The research results provide important basic data and theoretical guidance for the prevention and control of A.variabilis and the enhancement of resource utilization value. |
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