Effect Of Sodium Acetate Supplementaion On Milk Fat Synthesis,rumen Fermentation And Microflora In Lactating Dairy Goats

Acetic acid is one of the most abaundant volatile fatty acids（VFAs）after carbohydrate fermentation in the rumen of ruminants.Acetic acid plays an important biological function mainly by participating in animal fat metabolism.In the mammary gland tissue of ruminants,acetic acid is not only an important energy source of the body,but also an indispensable precursor of milk fat synthesis.On the one hand,milk fatty acids are derived from the intake of medium-and long-chain fatty acids by breast epithelial cells from the blood,and on the other hand,from the de novo synthesis of volatile fatty acids in the rumen.The nutrients in ruminant diet are first transformed into small molecular substances that can be used by the body through the degradation of rumen microorganisms,and then enter into each system to function.Therefore,this experiment studied the effect of sodium acetate on milk fat synthesis of dairy goats by adding sodium acetate to diet,which has important theoretical basis and practical significance for improving milk quality of dairy goats.A single factor experimental design was adopted in this study.30 dairy goats with 2parity,in mid-lactation（60 ±5 d）and similar body weight were randomly divided into three groups.The effects of sodium acetate on lactation performance,milk fatty acids and milk fat synthesis related genes of dairy goats were studied by feeding basic diet（CON group）,basic diet + 30 g/（d ·head）sodium acetate（group Ⅰ）and basic diet +60 g/（d ·head）sodium acetate（group Ⅱ）.The effect of sodium acetate on rumen microorganisms was discussed by 16 S r DNA sequencing technique,and the function and epigenetic modification of sodium acetate on milk fat synthesis were verified by adding sodium acetate to mammary epithelial cells.The main results are as follows:（1）Effect of sodium acetate on milk fat synthesis of dairy goats.Compared with CON group,the milk yield and milk fat rate of group Ⅰ and group Ⅱ increased significantly（P < 0.05）,but there was no significant difference in milk protein rate,lactose rate and non-fat milk solid（P > 0.05）.The percentage of palmitic acid（C16:0）in group Ⅰ and group Ⅱ was significantly higher than that in CON group（P < 0.05）,while the percentage of γ-linolenic acid（C18:3n6）was significantly lower than that in CON group（P < 0.05）.The percentage of α-linolenic acid（C18:3n3）in group Ⅱ was also significantly lower than that in CON group（P < 0.05）.Compared with CON group,the expression of FASN,SCD1 and ACACA,the key genes of milk fat synthesis in group Ⅱ was not significant（P > 0.05）,but had an increasing trend.In the detection of blood biochemical indexes,the serum globulin（GLB）in group Ⅰ and group Ⅱ was significantly higher than CON group（P < 0.01）,and the content of serum total protein（TP）in group Ⅱ was also significantly higher than that in group CON（P < 0.05）.The content of serum albumin（ALB）and white globulin ratio（A/G）in group Ⅱ were significantly lower than those in CON group（P < 0.05）.（2）Effect of sodium acetate on rumen microorganisms of dairy goats.The results of rumen volatile fatty acids showed that the changes of acetic acid and total volatile fatty acids were not significant（P > 0.05）,but the ratio of acetic acid to propionic acid increased.Through high-throughput sequencing of the V3-V4 region of 16 S r DNA gene in the rumen fluid of dairy goats,the results of Alpha and Beta diversity showed that the diversity and richness of rumen fluid microflora in group Ⅰ and group Ⅱ were higher than those in CON group,but the difference was not significant（P > 0.05）.Species composition analysis showed that Bacteroidetes and Firmicutes were the dominant bacteria in the rumen fluid of dairy goats,and Prevotella₁ was the dominant genus.At genus level,the abundance of Ruminococcus₁ in rumen fluid of dairy goats in group Ⅰ was significantly higher than that in group CON（P < 0.05）,Prevotellaceae_UCG-001 in rumen fluid of dairy goats in group Ⅱ was significantly higher（P < 0.05）,and the abundance of Fibrobacteraceae in rumen fluid of dairy goats in group Ⅰ and group Ⅱ was significantly higher than that in group Ⅱ（P < 0.05）.The analysis of rumen microbial function in dairy goats found that it was mainly involved in carbohydrate metabolism,amino acid metabolism,membrane transport and energy metabolism.The correlation analysis results show that there was a significant positive correlation between Prevotella₁ and total volatile fatty acids（P <0.05）,a significant negative correlation between Ruminococcus₁ and butyric acid（P< 0.05）,and an extremely significant positive correlation between Prevotellaceae_UCG-001 and C18:3n6（P < 0.01）.（3）Study on the effect of sodium acetate on milk fat synthesis in dairy goat mammary epithelial cells.The results of RT-q PCR showed that the expression of genes related to lipid metabolism（PPARG,SREBP1,INSIG-1）was significantly upregulated（P < 0.05）and the genes of de novo fatty acid synthesis and desaturation（ACACA,FASN,ACSS2,SCD1）,lipoprotein transport（FABP3）and triglyceride synthesis（GPAM,DGAT1）were extremely significant up-regulated（P < 0.01）when the concentration of sodium acetate was 12 m M,while the expression of ACSL1 gene was significantly down-regulated（P < 0.05）.By detecting the fatty acid composition of breast epithelial cells,it was found that with the addition of sodium acetate,when sodium acetate was added to 4 m M,the proportion of C6:0 was significantly higher than that of other groups（P < 0.05）,and the proportion of C4:0 was extremely significant higher than that of other groups（P < 0.01）,and the proportion of C22:1n9was significantly higher than that of 12 m M sodium acetate.When sodium acetate was added to 8 m M,the proportion of C:12 was significantly higher than that of other groups.When sodium acetate was added to 12 m M,the proportion of C16:0 and C18:0 was extremely significant increased in a dose-dependent manner(P < 0.01.The results of intracellular oil red and triglyceride contents showed that compared with the control group,the relative contents of oil red O and triglyceride increased significantly when sodium 12 m M acetate was added（P < 0.01）.The results of Western Blot assay showed that when the concentration of sodium acetate was 12 m M,the expression of histone H3K29 ac was extremely significant（P < 0.05）,while the expression of histone H3K27 ac was not significant（P > 0.05）,but had an increasing trend.To sum up,the effect of sodium acetate on milk fat synthesis was proved by adding sodium acetate in vivo and in vitro in this study,and the main microflora affecting milk fat synthesis were screened by 16 S r DNA sequencing.The results provide reference for milk quality improvement of dairy goats and provide theoretical and experimental basis for further elucidating the regulation mechanism of sodium acetate on milk fat synthesis of dairy goats.