Cts Of Intra-Arterial Infusion Of Fatty Acids And Amino Acids On Mammary Gland Lipid Metabolism In Lactating Dairy Cows

The objective of this study was to determine the effects of intra-arterial infusion of fatty acids and amino acids on milk fat synthesis in the mammary gland of lactating dairy cows, providing theoretical basis for further exploring the interaction between milk fat synthesis and milk protein synthesis.Experiment 1 studied the effects of intera-arterial infusion of acetate and long-chain fatty acids on fatty acids composition in artery and vein, mammary extraction and mammary balance. Eight multiparous Chinese Holstein cows (DIM=99±11d; parity,2～3) fitted with intra-arterial catheter were administered 2 treatments in 2×2 multifactor cross experiment design. The two diet treatments were mixed forage ration (MF) consisted of hay, corn silage and alfalfa as forage and CS diet featured with corn stover as only forage. The overall experiment period was 54 day with 27 days each period, including 21-day preliminary period and two continuous 3-day infusion periods. During the first 3-day infusion, both of MF and CS were infused with carriers featured with MFcl and CSc. During the second 3-day infusion, MF was infused with carriers (MFc2), whereas CS was infused with mixed fatty acids emulsions (CSf). CSf tended to increase milk fat content relative to CSc, but did not influence milk fat yield. Compared with CSc, CSf had tendency to increase the extraction rate of total fatty acids, C16:0, C18:0, C18:1 and C18:3, while increased extraction rate of C18:2n-6 to the same level of MFc2. In addition, mammary balance of C8·0, c10:0 and C12:0 for CSf were significant higher than that of CSc. Results indicate that acetate and long-chain fatty acids infusion tended to increase milk fat content and significantly increased mammary ectraction of C18:2n-6. And mixed fatty acids infusion markedly increased mammary synthesis of C8:0, C10:0 and C12:0, which illustrated the positive effect of acetate to de novo synthesis could overrided the inhibition caused by C18 FA.Experiment 2 was conducted to study the effects of intra-arterial infusion of amino acids on milk fatty acids composition. Eight multiparous Chinese Holstein cows (DIM= 99 ± 11d; parity,2～3) fitted with intra-arterial catheter were used in a one-factor experimental design based on CS diet. The experimental period was 27 day, including 21-day preliminary experiment and two continuous 3-day infusion periods. During the infusion periods, cows were infused with carriers for the first 3-day (CSc) followed by 3-day amino acids infusion (CSa). The results shows that CSa significantly increased milk fat content, while it had no influence on milk yield, milk fat yield, milk protein content. The milk concentrations of C4:0, C6:0, C8:0, C10:0, C12:0, C14:0 and C16:0 for CSa were lower than that of CSc, giving rise to the lower concentration of total short- and medium-chain fatty acids of CSa. However, the concentration of C18:0, C18:2n-6 and C18:3n-3 were not affected by amino acids infusion. Therefore, amino acids provided by intra-arterial infusion can decrease the concentration of shor- and medium-fatty acids in milk, but increased milk content, meanwhile, it did not affect total milk fat synthesis.Based on the experiment 2, the objective of this part was to evaluate the fatty acids composition in artery and vein and mammary lipid synthesis in order to study the possible interaction between milk fat precursors and milk protein precursors. Results indicate that amino acids infusion decreased the concentrations of long-chain fatty acids in both of artery and vein, but did not influence the total extraction rate of long-chain fatty acids. Moreover, marnmary de novo synthesis of C8:0, C10:0 and C14:0 were declined by amino acids infusion, which had no influence on mammary balance of C 18:1, C81:2n6 and 18:3n3. Therefore, intra-arterial infusion of amino acids can alter the fatty acids composition in artery and vein. In addition, the fatty acids arising from de novo synthesis were decreased by amino acids infusion, which did not influence long-chain fatty acids uptake from mammary artery.