| In this experiment, external pudendal artery(EPA) cannulation techniques were used to study the impact of infusing amino acids (AA) or fatty acids(FA) into EPA of dairy cows feeding the ration that corn straw(CS) is a single roughage on lactation performance, the levels of arterial concentrations of AA and its uptake rules in mammary gland, and, to explore whether the lower milk yield, milk protein and fat production is related to the concentration of milk component precursor supplied by EPA blood.The results may provide a theoretical basis for scientific and reasonable utilization of corn straw. Eight healthy Holstein cows with similar parity, body weight, lactation period(99±11d), and milk yield(20.17=1.28 kg/d) were randomly assigned in 2 groups with 4 cows each. A 2 x 2 cross-design were used in this study. Two different diets were formulated:Mixed forage(MF) diet containing alfalfa, Chinese wild hey and corn silage; and CS diet with only corn stalks that contained the same roughage ratio with the MF diet. The experiment was divided into two phases, the first phase consisted of 14 days of preliminary period and 9 days of infusion period, and CS group was infused carrier(C), AA or FA respectively, and MF group was infused C only during the first phage. The infusion of MF group and the CS group were interchanged during the second phase. Milk and blood were collected in the last two days during each infusion to determine the effect of the infusion of amino acid or fatty acids on uptake rules in mammary glands of dairy cows.The study was divided into three parts. Experiment one was conducted to study the effects of EPA infusion amino acid or fatty acids on milk yield, milk protein yield and milk protein rate. Experiment two investigated the impacts of infusion amino acid or fatty acids on the concentration and the ratio of amino acid in caudal. Experiment three primarily explored the effects of infusion amino acid or fatty acids on amino acid uptake and utilization in the mammary gland.Under the present experiment conditions, the study indicated that:(1) Compared with EPA infusion C, infusing AA could significantly improve the content of milk protein, total amino acid (TAA), branched-chain amino acid(BCAA), limiting amino acid(LAA), essential amino acid(EAA) and non-essential amino acid (NEAA) contents of milk dairy cows for CS group, and could tend to be significantly reduce fat corrected milk, milk yield and milk protein yield than MF, but the difference between the MF group and CS group was reduced.(2) Compared with infusion C for CS dairy cows, infusing FA could improve the content and synthesis efficiency of milk protein, while the content of milk AA was not significantly affected. The differences between the CS and MF in fat corrected milk, milk yield and milk protein yield were reduced, but all of these parameters in CS group were still significantly or tended to be significantly lower than in MF group.(3) Infusion AA though for CS dairy cows could significantly increase the concentration of TAA, EAA, NEAA and BCAA, as well as the contents of Asp, Ser, Ala, Leu, Lys, His, Glu and Ile of the caudal artery, and significantly or tend to be significantly improve the supply of each AA and plasma flow. Intake efficiency of mammary gland on most AA was significantly reduced.(4) Infusion FA for CS dairy cows could significantly or tend to significantly depress the content of TAA, EAA and LAA of the caudal artery. The plasma flow and the daily supply of each AA tended to be improved. The difference in the arteriovenous concentration of AA had a downward trend, especially EAA and LAA were significantly reduced. But there was little effect on the uptake efficiency and AA intake.(5) The low concentration of amino acids, insufficient supply of amino acids and large difference in amino acids arteriovenous concentration were probably the main reasons that the milk production and milk protein yield in CS group were lower than in MF group. |
PDF Full Text Request