Study On Mechanism Of Milk Protein Synthesis And Nutritional Modulation In The Lactating Ruminant

This paper mainly studied on mechanism of milk protein synthesis and nutrition modulation in lactating goats by nutrients infusion technique and arterio-venous technique.Firstly,it was analyzed and evaluated that effects of the levels of intestinal absorption AA on the arterial concentrations of AA and mammary uptake rates of AA. Secondly, the first limiting AA for milk protein synthesis (Met) in dairy cows fed on ordinary diet is studied to observe the effects of intravascular administration of two mixtures of amino acids including (+M) or excluding (-M) Met on mammary uptake rate of amino acids .The results showed that the mammary blood supply of the profile of amino acids could limit milk protein secretion and affected mammary metabolism.It was suggested that milk protein synthesis could be improved by regulating mammary blood supply of the profile of amino acids and increasing mammary uptake of amino acids.Trial one Effect of abomasal infusions of sodium caseinate on milk secrection and mammary uptake and utilization of individual amino acid in lactating goatsIn 3x4 incomplete Latin Square desige,three Shaneng goats(35 ± 5kg) with the same milk yield,fitted with permanent abomasal cannulas,and embeded carotid artery under the skin were used to investigate the effect of abomasal infusions of sodium caseinate,which was 0,33,66 and 99g/d,on mammary metabolism of amino acids and milk secretion in lactating goats.The results showed averaged yields of milk ,CP (milk N × 6.38) and milk fat trended to inrease as levels of abomasal infusions of casein increased, and increased respectively 17.39,28.35 and 15.02% on the control treatment, but these responses were not significant among three casein treatments(p>0.05). Milk fat and CP percentage remained unchanged.Mammary plasma flow was not significantly affected by added casein (p>0.05).Arterial concentration of essential amino acids increased significantly as infusions of casein increased. Arterial concentration and uptake of nonessential amino acids except Pro, Glu and Tyr were not significantly affected by casein treatment, and uptake was insufficient toaccount for output of nonessential AA residues in milk protein. Mammary uptake of individual EAA was compared with EAA secretion in milk protein, and the results showed some essential amino acids(Lys,Arg,Val and lie) were taken up in excess of their secretion into milk proteins,but others(His,Met,Leu and Phe)were almost exclusively extracted by the udder in a direct ratio to their output, which suggested mammary utilization of EAA was higher and mammary uptake of EAA mainly synthesised milk protein. Mammary tissue may exist physiological controls involved in regulating mammary uptake according to requirements of milk protein products.Trial two Effect of intrvenous administration of two mixtures of amino acids on milk secrection and mammary uptake and utilization of individual amino acid in lactating goatsIn 2x3 crossover desige,two Shaneng goats(35 ± 5kg) with the same milk yield,fitted with permanent cannulas,and embeded carotid artery under the skin were used to investigate the effect of intrvenous adminitration of two mixtures of amino acids.which was an amino acid mixture (60g/d) including (+M; 1.39g/d) or excluding(-M) Met,on mammary uptake of amino acids and milk secrection in lactating goats.The results showed that yields of milk (p<0.01) , CP (milk N x 6.38)(P<0.01) and CP( milk N x6.38) content (p<0.05) significantly inreased 12.99,4.92 and 18.33% during +M infusion. Fat percentage in milk was decreased from 3.99 to 3.70% by +M infusions so that the ratio of protein to fat climbed from 0.97 on the -M to l.l(p<0.05).It was suggested that the ratio of protein to fat was a sensitive indicator of Met imbalance. Removal of Met from the infusate caused arterial plasma Met concentration to drop 56.55 %(p<0.05),those of other amino acids changed little. The low levels of plasma Met caused the mammary blood supply of profile of AA change. As a result, the changes of mammary physiological metabolism also took place : 1) mammary plasma flow increased 39.79% 2) the mammary gland s capacity to remove plasma Met increased 46.82%,whereas the glands capacity for other amino acids declined.Thus ,the higher mammary plasma flow may offset mammary blood of Met deficiency so that milk protein yield decreased from 35.18 to 29.73g/d.