Study On The Precursor Of Milk Protein Of Mid-lactating Dairy Cows Fed Different Diets

The experiment was designed to study the effects of feeding different diets (basedon the feeding patterns of farmers and farms) on the utilizations of nitrogen and aminoacids. Twenty-four mid-lactating Holstein dairy cows with similar DIM, weight andparity were chosed and twelves of them were fitted with abomasal cannulation andrumen catheterization. These cows were randomly divided into two groups and eachgroup contained six cows with abomasal cannulation and rumen catheterization andsix without. The cows fed two different diets and the ratio of forage to concentratewas60:40and40:60. The forage of one diet was corn straw (CS) and the other diet’sforage was mixed with Chinese wildrye, alfalfa hay and corn silage (MF). Theexperiment lasted63days.The results suggested that:(1) There were no differences of the intakes of nitrogenand fecal nitrogen between the two groups (P>0.05),but the ratio of fecal nitrogen tointakes of nitrogen was significantly higher in MF group than that in CS group (P＜0.01). In CS group, the output of urinary nitrogen was higher than CS group (P<0.05).There was no difference of milk nitrogen was observed in the two groups (P>0.05).The transformation efficiency of feed nitrogen to milk protein was higher inMF(P<0.05), while transformation efficiency of feed nitrogen to ture protein andsedimentation nitrogen had no differences (P>0.05). The biological value of proteinand utilization ratio of net protein were higher in MF, but no differences wereobserved in the two groups (P>0.05). The concentration of ammonia nitrogen washigher in CS than that in MF (P<0.05) and it showed regular changes. The blood ureanitrogen was higher in CS than that in MF (P<0.05) and the concentration wasincreased after feeding.(2) There were no differences of the digestibilities of total amino acids, essentialamino-acid and non-essential amino acid between the two groups (P>0.05). Thedigestibility of all the amino-acid was higher than50%.(3) There were no differences of blood flow and the supplementation ofamino-acids between the two groups (P>0.05). The concentrations of amino-acids in artery were higher than in vein. Arteriovenousdifferences of Phenylalanine in CS tended to be higher than in MF (P=0.10)andaspartic acid was higher in MF than in CS (P<0.05). In all, arteriovenous differencesof total amino acids, essential amino-acid and non-essential amino acid had nodifferences between the two groups (P>0.05).There were no difference of the productions and ratios of amino acids, totalessential amino acids and total non-essential amino acids between the twogroups(P>0.05).The intake efficiency of aspartic acid in MF significantly higher than in CS(P<0.05), while no differences of the other amino-acids were observed (P>0.05). Thetransformationefficiency of phenylalanine in MF was significantly higher in MF thanin CS (P<0.01),while the threonine, aspartic acid and serinewas lower in MF than inCS (P<0.05).