Effects Of High DHA Microalgae Powder On Digestion And Metabolism,Rumen Fermentation And Fatty Acid Composition Of Milk Fat In Dairy Cows

The subject of this experiment is to study the optimal amount of high-DHA microalgae powder for the production of DHA-rich functional milk.In this experiment,the effects of nutrient digestibility,rumen fermentation,rumen microflora,enzyme activity,blood antioxidant indexes,milk production performance,and milk fatty acid composition were studied by combining the semi-in vivo method and lactating dairy cow feeding experiment.It provides a theoretical basis for the production of DHA-rich functional milk by adding high-DHA microalgae powder to the dairy cow’s diet.Experiment 1: four 18 month old Holstein dairy bulls with permanent fistulas weighing 570±2.5 kg were randomly assigned to a 4×4 Latin square design.The treatments were designed as :control(without DHA),LDHA,MDHA,and HDHA with 100,200,300 g DHA per steer per day,respectively.The experiment lasted for 80 days.Results:Dietary supplementation of 300 g high DHA microalgae powder significantly reduced the effective degradation rate of NDF in rumen(P<0.05).At 6 h after feeding,the concentration of NH3-N in rumen fluid decreased significantly with the increase of microalgae powder dosage(P<0.05).At 3 h after feeding,200 g microalgae powder significantly increased the total VFA production in rumen(P<0.05).At 6 h after feeding,200 g and 300 g microalgae powder significantly decreased rumen A: P value(P<0.05).Before feeding,300 g of microalgae powder significantly reduced the abundance of rumen white rumen cocci and rumen yellow rumen cocci(P<0.05).At 3 h after feeding,200 g microalgae powder significantly increased the abundance of rumen amylop Hilic in rumen(P<0.01).At 3and 6 h after feeding,200 g and 300 g microalgae powder significantly reduced the abundance of protozoa in rumen(P<0.05).The concentration of free fatty acids in plasma increased significantly with the increase of microalgae powder(P<0.05).The concentration of thiobarbital reactants in plasma increased significantly with the increase of microalgae powder dosage(P < 0.05).Comprehensive analysis of the indicators,the optimal addition of high DHA microalgae powder is 200 g.Experiment 2: Thirty lactating cows with similar body weight(675±21 kg),parity(3.5±0.2),lactation days(97±12 d)and milk yield(30±2.4 kg)were randomly divided into two groups and fed with basal diet and basal diet + 200 g microalgae powder respectively.The cross experiment design was used to carry out three 90 day lactation experiments.Result:Dietary microalgae powder significantly reduced the concentration of ammonia nitrogen in rumen fluid(P<0.05),and the abundance of protozoa in rumen fluid significantly decreased(P<0.05).The activities of superoxide dismutase,thiobarbituric acid reactants and malondialdehyde in blood antioxidant indexes were higher than those in control group(P>0.05).Compared with the control group,the dry matter intake and standard milk volume had no significant change,the milk yield increased significantly(P<0.05),but the milk fat rate decreased significantly(P<0.05).Microalgae powder significantly changed the fatty acid composition of milk fat,increased the proportion of unsaturated fatty acids and decreased the content of saturated fatty acids(P<0.05),especially significantly increased the DHA content of n-3 polyunsaturated fatty acids in milk fat(P<0.05),up to 0.59 g / 100 g milk fat.Conclusion:Adding 200 g microalgae to dairy diet improves the performance of dairy cows,and can produce DHA rich milk.