The Effect Of Supplementing Astragalus To Weaned Yak Calves On Growth Performance And Physiological Metabolism

It is urgent to improve immune ability and reduce stress of livestock through nutritional regulation measures.Especially for newly weaned calves,their rumen are still not fully developed which hampered the nutrients absorption and metabolism.As a traditional Chinese herbal medicine,astragalus has been widely used in clinical practice,especially its medicinal function.In present study,astragalus dried root and water extract?ARE?were used to carry out in vitro fermentation and supplanting to weaned yak calves,respectively.The objective is to reveal the health and immunity promoting function of astragalus as feed additives to yak calves,and to provide scientific evidence for the future use of astragalus in livestock production.Experiment I The effect of astragalus superfine power and antibiotics on in vitro rumen fermentationAlfalfa hay was used as fermentation substrates in the in vitro fermentation experiment.The astragalus superfine powder?Astra.?and tetracycline?Antib.??5%of dried Alfalfa hay,respectively?were added.The control?CK?was only alfalfa hay.The results were as the following:?1?At the different sampling time,the dry matter degradation rate of Astra.was significantly higher than that of the other two treatments?Antib.And CK??P<0.05?.During the fermentation process,compared with Antib.Treatment,the concentration of total volatile fatty acids?TVFA?were significantly increased in CK and Astra.groups?P<0.05?.The TVFA concentration of Astra.treatment was significantly higher than that of CK and Antib.treatments?P<0.05?.?2?After 16Sr RNA gene sequencing,the dominant bacteria groups at the phylum level were Bacteroidetes,Proteobacteria and Firmicutes.The Firmicutes in the control group and astragalus group were significantly increased?P<0.05?,while those in the Antib.group were significantly decreased?P<0.05?.Proteobacteria were significantly increased in the astragalus group?P<0.05?.Prevotella₁ was the dominant bacterium in the three treatment groups at the genus level.During the fermentation process,the Astra.and Antib.had significantly lower levels of prevotella₁?P<0.05?,but it was significantly higher in Astra.group than the other two groups?P<0.05?.Experiment II The effect of supplementing different levels of astragalus root extract on growth performance and rumen fermentation of weaned yak calvesTwenty-four male yak calves,six to seven months of age,were used in a 75 d feeding trial.They were assigned randomly to one of four dietary treatments that differed in supplementary astragalus root extract?ARE??0,ARE₀,20,ARE₂,50,ARE₅,and 80,ARE₈,mL/kg dry matter intake?,with 0 g/kg as control.The results were as the following:?1?The average daily gain?ADG?of calves in the group with supplementing ARE was significantly higher than without?P<0.05?.The feed conversion rates?ADG:DMI?in ARE₅ and ARE₈ groups were significantly higher than the other two groups?P<0.05?.?2?The acetate concentration of ARE₈ group was significantly higher than the other groups?P<0.05?.The concentration of total volatile fatty acids?TVFA?in ARE₀,ARE₂ and ARE₅ groups increased with the extension of feeding time?P<0.05?.The TVFA in ARE₈ group was significantly higher than the other three groups?P<0.05?.Experiment III The effect of supplementing different levels of astragalus root extract on serum physiological and biochemical indexes of yak cavesThe experimental design is the same as experiment II.The results were as the following:?1?The total antioxidant capacity?T-AOC?,superoxide dismutase?SOD?and insulin?INS?in serum increased significantly with the increase of feeding time?P<0.05?.On the 60th day of the experiment,the serum SOD concentration in ARE₈group was significantly higher than the other three groups?P<0.05?.The T-AOC in ARE₀ group was significantly lower than the other three groups?P<0.05?.?2?The supplementing ARE to yak calf significantly increased serum immunoglobulin A?IgA?,immunoglobulin G?IgG?and immunoglobulin M?IgM?concentrations,which also increased with feeding time?P<0.05?.The IgA concentration of ARE₈ was significantly higher than other three treatments on day 60?P<0.05?.The IgG concentrations of ARE₅ and ARE₈ were significantly higher than ARE₀ and ARE₂ on day 60?P<0.05?.?3?The concentration of serum tumor necrosis factor?TNF-??decreased with feeding time in all the four groups?P<0.05?.The serum interleukin-6?IL-6?concentration in ARE₈ group was significantly higher than the other three groups?P<0.05?.Experiment IV The effect of supplementing different levels of astragalus root extract on ruminal microbiota of yak calves.The experimental design is the same as experiment II.The results were as the following:?1?At the phyla level,Firmicute,Bacteroidetes and Proteobacteria were the dominant phyla of calves?42.5,48.1 and 1.14%of the OTUs,respectively?.With the increase of ARE level,the proportion of Firmicutes,Proteobacteria and Actinobacteria increased?P<0.05?,while the proportion of Bacteroidetes decreased?P<0.05?.?2?Total of 79 bacterial genera were detected,among which the core genera were Rikenellaceae RC9?15.5%?,Succiniclasticum?13.9%?and Prevotella 1?12.5%?.The abundance of Rikenellaceae_RC9_gut_group,Succiniclasticum and Prevotella₁in ARE₅ and ARE₈ groups was significantly higher than that in ARE₀ group?P<0.05?.In conclusion,the current study found that supplementing ARE to weaned yak calves increased the average daily gain,feed utilization efficiency.Ruminal acetate and propionate concentrations,and antioxidant status and immune responses were all increased with supplementary ARE.Furthermore,ARE supplementation increased rumen microbial diversity and the abundance of fibre degrading microbes.We concluded that ARE can be used as an effective botanical feed additive to improve livestock production and that supplementation at 50 mL/kg to 80 mL/kg DMI was an appropriate level.