| Milk long chain fatty acids (LCFA) are mainly from diet octadecenoic acids which absorbed in intestine. Enhancing milk LCFA content might be good at cinsumer's health. Our study aims to estimate postruminal octadecenoic acids requirement for lactation in dairy cows.Experiment 1 studied relationship between duodenal flows or postruminal infusion of C18 fatty acid and the correponding fatty acid concentrate in milk fat or daily yield, using a meta-analysis of database 15 experiments. Additionally we also measured the effect on DMI in lactating dairy cows. The data from duodenal fows of 18C fatty acids showed that, stearic acid had largest daily flow, but a lowest appearent transfer rate to milk. Whereas, postruminal flow of oleic acid, linoleic acid, and linoleinc acid had linear relationship with the corresponding fatty acids in milk fat. Postruminal infusion of oleic acid, linoleic acid, and linolenic acid also lineary increased milk those corresponding fatty acids, however with daily yield of oleic acid and linoleic acid in milk were showed quadrautic type of changes, they were appeared that increased firstly then decreased with the infusion amount increased. In this point, data of linolenic acid was less sufficient. Postfuminal supply increasing amount of 18C fatty acids quadratically affected DMI in lactating cows, the inflextion point showed in 400-450 g/d.Increasing theα-linolenic acid content of milk fat might be desirable to meet consumer's health care. Objective of experiment 2 was to determine the potential to alter the content of C18:3 in milk by duodenal infusion of a high C18:3 free fatty acid mixture. Four multiparous Chinese Holstein cows (BW = 556±19 kg, DIM = 93±9 d) fitted with duodenal cannulas were administered 2 treatments in a crossover design. Treatments were homogenized aqueous mixtures ofα-linolenic acid (LNA; 82.4% cis-9, cis-12, cis-15 18:3; 14.7% cis-9, cis-12 18:2; 2.8% cis-9 18:1) or control containing only the emulsifying ingredients. The control infusate consisted of 15 g/d of xanthan gum, 5 g/d sodium alginate, and 25 g/d of Tween 80 in 10 L of water. Each period lasted 5 wk, in which 2 cows received each amount (0, 40, 80, 120, and 160 g/d) of LNA for 1 wk each, and the other 2 cows received only the carrier infusate. Measurements were made during the last 3 d of each infusion amount. Dry matter intake and total tract apparent digestibilities of nutrients were not affected by LNA infusions. Milk production tended to decrease and quadratically affected as LNA infusion increased but production of 4% FCM was not changed. Milk fat content tended to increase linearly with LNA infusion. Milk protein content was not changed by LNA infusion, whereas milk lactose content and yield were lower for LNA vs. control and decreased quadratically as LNA infusion increased. Increasing the amount of LNA infused into the duodenum linearly increased concentrations of cis-9, cis-12, cis-15 C18:3 (0.61 to 25.4 of total fatty acids) and cis-9, cis-12 C18:2. Increasing LNA decreased percentages of C4:0, C14:0, and C16:0 so that total≤16C fatty acids decreased linearly. Increasing LNA linearly decreased percentages of cis-9 C18:1 and cis-9, trans-11 C18:2 in milk fat. Milk fat content of cis-5, cis-8, cis-11, cis-14, cis-17 C20:5 was quadratically affected, whereas concentrations of C18:0, trans-9 C18:1, trans-11 C18:1, and trans-10, cis-12 C18:2 were not affected. Increasing the supply ofα-linolenic acid to the small intestine linearly increasedα-linolenic acid in milk fat and markedly altered milk fat composition. Experiment 3 was continuation of experiment 2. We used 0, 100, 200, 300 and 400 g/d as LNA infusion amount measured effects on DMI, milk production, milk composition, and milk fatty acid composition in primparious lactating dairy cows. Milk fat and protein content were linearly increased with increasing amount of LNA infused into duodenum, whereas, milk lactose content was decreased linearly. Fatty acid profile in milk fat was significantly altered as LNA infusion as the similar paterns of experiment 2. SFA and MUFA in milk fat decreased linearly as LNA infusion amount increased, PUFA content was increased linearly duo to LNA concentration sharply increased with treatment. Daily yield of LNA in milk was quadruatically affected by increasing amount of duodenal LNA infusion, the reflextion point was showed at the amount of 300 g/d.In experiment 4, we conducted to use five duodenal cannuled Holstein dairy cows to study effect of duodenal infusion of variable 18C fatty acids of DIM, milk production performance and milk fatty acid profile. 5×5 latin square design was used, treatment were A: infusion amount was 400 g/d free fatty acids mixtures of oleic acid + linoleic acid + linolenic acid + stearic acid; B: infusion amount was 388 g/d free fatty acids mixtures of oleic acid + linoleic acid + stearic acid; C: infusion amount was 382 g/d free fatty acids mixtures of oleic acid + linolenic acid + stearic acid; D: infusion amount was 184 g/d free fatty acids mixtures of linoleic acid + linolenic acid + stearic acid; and E: infusion amount was 246 g/d free fatty acids mixtures of oleic acid + linoleic acid + linolenic acid, respectively. Each period lasted 21 d, including 14 d adaptation and a 7 d of data collection. Withdrawl of specific 18C fatty acid from infusate were not affected DMI, milk yield, and milk composition compared to A treatment. Except stearic acid, withdrawl one of specific 18C fatty acid form the whole mixture of infusate decreased corresponding fatty acid concentrations in milk fat. When withdraw oleic acid from the infusate, increased stearic acid concentration and tended to increase linolenic acid in milk fat. The results suggesting that, postruminal oleic acid, linoleic acid, and linolenic acid amount are the restriction factor of corresponding fatty acids concentration in milk fat; oleic acid may be an inhibition factor to stearic acid and linolenic acid uptake by mammary gland during lactation.
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