Effects Of Schizochytrium Sp.and Lactoferrin On Growth And Gastrointestinal Health Of Pre-weaning Dairy Calves

In this research,dairy calves were used to investigate the effects of Schizochytrium sp.(SZ)on growth performance,rumen fermentation function,antioxidant capacity and immune function.Furthermore,according to the result of the first experiment,evaluating of Schizochytrium sp.(SZ)and lactoferrin(LF),both individually and in combination,for their ability to improve growth,feed utilization,gut health,and fecal microbiota in dairy calves challenged with Escherichia coli K99(E.coli K99)before weaning were performed.The specific research content is as follows:Experiment 1:This study aimed to determine the effect of different levels of SZ supplementation on the growth performance,rumen fermentation function,antioxidant capacity and immune function of dairy calves.Fifty newborn female Holstein calves were randomly assigned to 5 groups(n=10).The 5 groups of calves were fed with whole milk supplemented with(per calf per d)0 g(control,SZ0),5 g(SZ5),10g(SZ10),20 g(SZ20),or 40 g(SZ40)of SZ powder from day 4 to 60.The results were as follows:1)The body weight and heart girth increased quadratically with the increasing SZ supplementation(P<0.05),SZ10 and SZ20 groups were higher than other groups at day 60.2)With the increasing SZ supplementation,average daily gain increased quadratically(P<0.05)between day 1 to 60,SZ20 group was numericallly higher than other groups;Feed-to-gain ratio decreased quadratically(P<0.05)between day 1 to 60,SZ20 group was numericallly lower than other groups.3)The concentrations of rumen isobutyric acid and isovaleric acid decreased linearly with increasing SZ supplementation at day 42(P<0.05).4)With the increasing SZ supplementation,the content of malondialdehyde and the activity of glutathione peroxidase increased linearly at day 28 and 60(P<0.05);the activity of catalase increased linearly at day 60(P<0.05).Considering the conditions of experiment,it is better to add 20 g/d SZ in dairy calves.Experiment 2:This aim of this study was determine the alleviating effects Schizochytrium sp.(SZ)and lactoferrin(LF)on diarrhea in dairy calves,and the growth performance,rumen fermentation function,serum index and fecal microbiota of dairy calves.Forty newborn male Holstein calves were randomly assigned to 4 treatments(n=10):Ctrl,fed whole milk only;LF,fed whole milk supplemented withlactoferrin(1 g/d);SZ,fed whole milk supplemented with Schizochytrium sp.(20 g/d);LF+SZ,fed whole milk supplemented with both lactoferrin(1 g/d)and Schizochytrium sp.(20 g/d)in a 2×2 factorial design.In day 7,all the calves were challenged with E.coli K99(10 mLx10~100 CFU/mL)orally.The results showed as follows:1)Fecal score in SZ group was significantly lower than Ctrl group at day 3(P<0.05).There were synergistic action of SZ and LF for decreasing fecal score at day 8,9,and 14(P<0.05);SZ,LF and LF+SZ were significantly lower than Ctrl group at day 8(P<0.05);LF was significantly lower than Ctrl group at day 9(P<0.05);SZ was significantly lower than Ctrl group at day 14(P<0.05).2)The activity of glutathione peroxidase calves in LF group was significantly higher than SZ and LF+SZ groups in blood(P<0.05).The SZ significantly increased the activity of superoxide dismutase in blood(P<0.05),and significantly decreased the concentration of tumor necrosis factor-?and D-lactic acid in blood(P<0.05)compared with control.The LF+SZ significantly increased the activity of superoxide dismutase and catalase,and the content of malondialdehyde in blood(P<0.05),and significantly decreased the concentration of tumor necrosis factor-?,lipopolysaccharides and nitric oxide in blood(P<0.05)compared with control.The concentration of Immunoglobulin G calves in SZ and LF+SZ groups were significantly higher than LF group in blood(P<0.05).3)SZ and LF increased the community diversity and abundance of fecal sample,however LF+SZ decreased the diversity of fecal sample in dairy calves,of which SZ increased the abundance of fecal Megamonas,and decreased the abundance of fecal unidentified Enterobacteriaceae and Veillonella,LF increased the abundance of fecal Bacteroides and Akkermansia,and LF+SZ increased the abundance of fecal Bacteroides.These results indicated that SZ and LF could reduce the fecal score of dairy calves and have a synergistic effect in reducing the fecal score of dairy calves,which can effectively relieve diarrhea in dairy calves through regulating intestinal microbial composition of diarrhea calves,improving intestinal permeability,reducing pro-inflammatory factors,improving antioxidant capacity and immune capacity.