Milk fat synthesis in dairy cattle nutrition metabolism regulation mechanism on
100 years, nutrient metabolism in dairy cows on milk fat synthesis during the formation of three kinds of theoretical models: is the rumen volatile fatty acids (volatilitfattyacid, VFA) changing pattern of the precursors of milk fat; is a glucose on insulin adipose tissue mobilization theory; is the fatty acid and its isomers on milk fat synthesis. Results show that dairy rations of various nutritional factors on the synthesis of milk fat with the combined effect of regulation.
1 rumen VFA pattern effect on milk fat precursors
Acid as the theory of milk fat precursors, such as due to Powell (1939), Balch, etc. (1952), Loosl, etc. (1945), MaClvmont, etc. (1950), Tyznik, etc. (1951) using high concentrate on low roughage food, Balch (1954), Blosser and other (1952), Putnam et al (1961) with chopped coarse material and granulation cows fed hay produced milk fat percentage decreased, acetic acid can be used rumen microorganisms, but also a synthesis of short chain fatty acids Raw material , ROOk, etc. (1964), Tyznik, etc. (1951) found that feeding Vinegar Cream can relieve lower sodium, while Balch, etc. (1955), Stoddard et al (1949) that the coarse material in low conditions, short chain fatty acids in milk fat was further reduced (Plamquist, 1993). Milk fat percentage decreased and rumen fermentation and rumen PH related (Powell, 1939). Emery (1964) reported carbonate can increase the milk fat, which made acetate / propionate ratio effect on milk fat, rumen VFA supplement and strengthen the theoretical model. However, test results and the conclusions contrary, McClymont (1950) and VanSoest et al (1959) found decreased blood levels of fatty acid is not relevant; fed high concentrate diets, the ruminal acetate did not decrease significantly (VanSoest, 1963 ). Bauman et al (1970) also found with the radioactive isotope method high concentrate diet had no effect on rumen VFA concentration, acetate did not lack, but the acetate / propionate ratio declined. Swan, etc. (1956), Hawkins, etc. (1959), Rook et al (1961) that feeding propionate also resulted in decreased milk fat. In the hunger strike, low nutrient levels or lower case intake, milk fat percentage increase, at this time rumen acetate / propionate ratio increased, but low levels of nutrition in long-term adaptive regulation of dairy produce, thereby reducing fat and non-fat solids content, which kind of adjustment process takes 2 1 4 weeks (Emery, 1973).
2 insulin-glucose and adipose tissue mobilization theory
Eckle (1916) that the hunger strike and low nutrition level, milking cows by the endocrine control mechanisms. Hormone may mobilize body fat, resulting in lipid, non-esterified fatty acids (non-esterifiedfattyacid, NEFA), blood ketone bodies, blood fat and improve activity, a transient increase in milk fat secretion. Insulin is associated with fat metabolism in one of the main endocrine hormones promote fat synthesis and inhibition of fat mobilization and decomposition. Intravenous infusion of glucose and glycerol lead to lower milk fat and glucose to promote insulin secretion, inhibition of lipid metabolism in pituitary factor, lower blood glycerol and NEFA levels. Cream can temporarily reduce insulin infusion (VanSoest, 1963). As the increase in plasma insulin result in fatty acid intake increased organization and make 5 times the body's insulin levels, while blood glucose remained unchanged, found no effect of insulin on milk fat synthesis.
Breast cells is a prerequisite for absorption of triglycerides in breast epithelial cells within the capillary surface lipoprotein lipase (liPoproteinllPase, LPL) under the action of triglyceride hydrolysis. LPL activity ratio from the lipoprotein lipid and protein type control, these factors are controlled by diet and hormones, lipids from adipose tissue transfer to the breast showing the breast with tissue-specific LPL, adipose tissue LPL activity than in the mobile layer high mammary gland LPL activity was higher at the bottom. Hormones on the regulation of LPL has specific and prolactin on the mammary tissue (presence of insulin under the conditions, 4h medium) LPL release and induced activities of help. Prolactin had no effect on fat tissue, but fat tissue in the 24h culture process, LPL activity by insulin regulation (McGuire et al, 1995). The beginning of lactation, breast lipoprotein lipase LPL activity increased 8 times, and lower adipose tissue LPL; low roughage diet reduced mammary LPL, LPL increased in adipose tissue (Askew, 1971).
Lipids in most physiological conditions (such as hunger, causative and stress) for the storage of energy, triglyceride hydrolysis before the first to be used by other organizations, the enzyme catalyzed hydrolysis known as the "hormone-sensitive lipase" ( hormonesensitivelipase, HSL, also called fat transfer enzyme), its role is similar to LPL. Fat storage decided to HSL, ester synthesis and adipose tissue LPL activity. Different dietary conditions or under lactation launched, with the secretion of milk fat, glyceride synthesis in adipose tissue LPL has changed dramatically, beginning lactation, adipose tissue fatty acid migration in the active enzyme content increased 1.6-fold (Sidhu, etc. , 1972).
HSL hormone-sensitive lipase by glycogen synthase and a CAMP dependent kinase phosphorylation are regulated, no active form of the enzyme kinase or CAMP caused by living under. Hormones affect the activity of hormone sensitive lipase, such as epinephrine, norepinephrine, glucagon and other rapid effect, while the chaff hormone, growth hormone and insulin inhibitor on the part of the role of acid green gland slower. Insulin decreased. AMP levels, inhibiting the hydrolysis of fat cells, lipids, thus reducing the number of HSL activity. In addition, HSL acts on triglycerides stored in fat cells, while the role of lipoprotein lipase in transit lipoprotein triglycerides. Hormones on the regulation of LPL is the level of protein synthesis and expression, lies on the regulation of HSL phosphorylation occur, has nothing to do with protein synthesis. Insulin reduced the activity of HSL, increasing the activity of lipoprotein lipase; contrast, catecholamines reduced lipoprotein lipase activity, increased HSL activity.
Dietary factors as fat reduction, although decomposition of adipose tissue triglycerides increased, but decreased the release of glycerol and fatty acids, which is caused due to re-synthesis of triglycerides to fatty acids in adipose tissue to circulating, fat tissue glycerides synthesis of fatty acids to regulate and control the release of priority in the HSL. Release of fatty acids esterified as triglycerides in the blood into the mammary gland for secretion or after the formation of fatty acid oxidation metabolism, if the fatty acids and glycerol esterification process in the proportion of the breast is not appropriate, the formation of excess energy, for milk and milk protein synthesis, suggesting that other factors also affect milk fat synthesis (Emery, 1973
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