Study On The Digestibility Of Protein Fraction C Of Dairy Cows Feedstuffs

Degradation and digestion rates of protein fraction C of kinds of Dairy feedstuffs weredetermined in this study,based on the method in cornell net carbohydrate and proteinsystem(CNCPS); The variations of the Milk yield and Milk compositions as a results ofadding Lys and Met to diet in different amounts, based on the digestion rates of proteinfraction C,were measured.Part1, Study on degradation rates of protein fraction C in rumenSix multiparous, ruminally cannulated Holstein dairy cows，with the similar milkproduction performance,were used to evaluate the degradation rates of protein fraction C of16kinds of feedstuffs by the rumen nylon bag method. The results indicated that proteinfraction C could be digested in rumen.And the degradation rates was higher for proteinfraction C in nonforage than in forage.Part2, Study on digestion rates of protein fraction C in intestineThe small intestinal digestion rates of protein fraction C in feedstuffs and ruminalresidues were established by the method of the three-step in vitro procedure (Calsamiglia andStern,1995). The results indicate that protein fraction C in feedstuffs can be digested in alarge extent. Especially, there is a significant difference on the digestion rates of proteinfraction C between feedstuffs and ruminal residues.The digestion rates of protein fraction C inruminal residues of DDGS、soybean meal and wheat bran are0%,others are between2.34%and44.25%. A significant difference of digestion rates was observed (P<0.01) when proteinfraction C of concentrates were degraded in rumen for12hours,besides peanut meal (P=0.15),On the contrary, the diversification of digestion rates of protein fraction C in coarse fodderswere not obvious besides alfalfa2(P<0.01).Part3, The study of appropriate proportion of Lys and Met in digestible protein ofintestine by feeding trial60dairy cows in early lactation period was fractionated to3groups(group A、B and C)by milk yield, to measure the appropriate proportion of Lys and Met in digestible protein ofintestine.Change the quantity of Lys and Met in digestible protein by addingRumen-protected lysine and Rumen-protected Methionine to diet. The variations of the milkyield and milk compositions as a results of adding Lys and Met to diet in different amountswere measured after feeding lactation cows of those three groups for60days. Finally, nosignificant difference was observed(P>0.05) from the result besides the Lactose(P=0.13).Theresults show that the three diets of different Lys and Met ratio have no significant effect on performance of early lactation dairy cows under the conditions of this experiment.