Effects Of Branched-chain Volatile Fatty Acids And Folic Acid On Growth Performance Of Holstein Dairy Bulls Based On Omics Technology

To study the effects of branched-chain volatile fatty acids(BCVFA)and folic acid(FA)on growth performance,nutrient digestibility,rumen fermentation and liver metabolism of holstein bulls,the experiment was divided into four parts.Part 1: Eight 9-month-old holstein calves were selected to study the effects of different levels of BCVFA on rumen metabolites and microbial flora.Part 2: This study evaluated the effects of BCVFA and FA on growth performance and nutrient digestibility of 8 Holstein dairy calves at the age of 60 days.Part 3: This study evaluated the effects of BCVFA and coated folic acid(CFA)on growth performance and nutrient digestibility of 12 Holstein dairy bulls at the age of 16 months.Part 4:This study investigated transcription m RNA expression of the liver tissue of bulls based on part 3.Part 1showed that the diversity of rumen bacteria was decreased(P<0.05)by supplementation of 20 mL/d BCVFA.BCVFA significantly reduced the relative abundance of Ruminococcus and Succinvibrio(P<0.05).The metabolites of rumen fluid and serum in 40 mL/d BCVFA group were separated from control group(VIP>1.0;P<0.05).The concentration of serum caffeic acid was higher for 20,40 and 60 mL/d BCVFA addition than for control(VIP>1.0;P<0.05).In part 2,the BCVFA×FA interaction was observed for the ratio of acetate to propionate,activity of cellobiase and ruminal microbial protein synthesis(P<0.05).The higher average daily gain and nutrient digestibility were observed for BCVFA or FA addition(P<0.05).Nitrogen retention/digestible nitrogen increased(P<0.05)with BCVFA addition,but was not affected by FA addition.Serum acetoacetate and somatostatin were increased by BCVFA,but were decreased by FA(P<0.05).Part 3 showed that the higher average daily gain,nutrient digestibility,nitrogen retention/digestible nitrogen and serum albumin,growth hormone and insulin-like growth factor-1 were observed for BCVFA or CFA addition(P<0.05).Rumen total volatile fatty acids oncentration,microbial enzyme activity,bacteria populations and ruminal microbial protein synthesis increased(P<0.05)with BCVFA addition.However,ruminal fermentation was not affected by CFA addition.Part 4 showed that among the genes involved in lipid metabolism pathway,CFA significantly increased the expression levels of CD36 antigen gene and LOC522146 in the liver,and significantly decreased the expression levels of LOC101906598(FC≥2).BCVFA significantly increased the expression of prostaglandin D2 synthase in liver(FC≥2).The interaction between FA and BCVFA significantly increased the expression of LOC512541 in the liver(FC≥2).In summary,the rumen microbial diversity and metabolites content changed with rumen BCVFA addition.Serum coffeic acid may be a marker metabolite to BCVFA addition.The growth performance of Holstein dairy bulls was improved with BCVFA,FA or CFA supplementation.The BCVFA×FA interaction was observed for the ratio of acetate to propionate,activity of cellobiase and ruminal microbial protein synthesis.