Effect Of A High Concentrate Diet On The Redistribution Of Free Amino Acids In The Liver And Milk Yield/Milk Protein In Dairy Goats And Its Mechanism

The purpose of this study was to explore the effect of a high concentrate diet on the redistribution of free amino acids in the liver and milk yield/milk protein in dairy goats. The research consists of three parts:1 The effect of a high concentrate diet on the redistribution of free amino acids in the liver in goats at their dry periodThe experiment selected 6 goats at their dry period and used a 2×2 Latin square design. The first 10d was the adaptation period, during which the rumen fistula surgery and vascular fistulas surgery were performed. After the adaptation period, the goats were randomly divided into 2 groups and were fed with forage with different concentrate ratios, 40:60 (the normal control group) and 60:40 (the high concentrate group), for 4 weeks each Latin square cycle. At the end of each cycle, blood was taken from jugular vein, hepatic vein and portal vein; rumen fluids were collected through the rumen fistula; liver tissues were also sampled. The pH value of rumen fluid was determined respectively at 0,1,2,4,6, 8 and 10 hours from feeding. Also determined the concentration of free amino acids in the blood of hepatic vein, portal vein and the liver homogenate, the LPS and MDA content in peripheral blood and the enzyme activity of SOD, CK, LDH, GPT and GOT in both peripheral blood and liver tissues. Results:Comparing the two groups, in the the high concentrate group:there were more amino acids in portal vein while less amino acids in hepatic vein, and the storage of free amino acids in liver also decreased; the pH value of rumen fluid declined by time and the goats were found to have SARA; the LPS content in peripheral blood had an extremely significant increase (P<0.01); the MDA content increased while the enzyme activity of SOD decreased significantly (P<0.05). In the peripheral blood of the high concentrate group:the enzyme activity of CK increased with no significance (P>0.05); the enzyme activity of LDH increased with extreme significance (P<0.01); the enzyme activity of GPT and GOT increased with significance (P<0.05); meanwhile in liver, the enzyme activity of these four increased but with no significance (P>0.05). These results suggest that a high concentrate diet could cause amino acids redistribution in liver, the amino acids entering into the liver being increased and the amino acids going out the liver being reduced. The mechanism might be that under a high concentrate diet, the organisms get SARA which causes the LPS content increasing in peripheral blood and leads to a weaker ability of antioxidant, thus inducing liver damage and the excessive consumption of amino acids.2 The effect of a high concentrate diet on the redistribution of free amino acids in the liver and the milk protein in lactating dairy goatsThe experiment selected 6 lactating dairy goats and used a 2×2 Latin square design. The first 10d was the adaptation period, during which the vascular fistula surgeries of hepatic portal vein, hepatic vein and femoral.artery were performed. After the adaptation period, the goats were randomly divided into 2 groups, were fed with forage with different concentrate ratios,40:60 (the normal control group) and 60:40 (the high concentrate group), for 8 weeks each Latin square cycle. At the end of each cycle, milk yield was measured with milk samples taken to determine the milk protein content. Blood was taken from the vascular fistula surgeries of hepatic portal vein, hepatic vein and femoral artery. Free amino acids in plasma were measured by RP-HPLC. Meanwhile jugular blood was also taken in order to determine the MDA content and the enzyme activity of SOD、GPT、GOT、AKP、 GT、LDH and CK in peripheral blood. Results:After 8 weeks of feeding, comparing the two groups, in the high concentrate group:milk yield declined (461.75±87.74 vs 403.10±21.40, P>0.05); the percentage of milk protein declined significantly (2.83±0.05 vs 2.65±0.03, P<0.05); in hepatic portal vein 14 kinds of amino acids all had a higher percentage while in hepatic venous they had a lower percentage except for Asn、Gln and Ile whose percentage were slightly higher; in femoral artery, these amino acids had a lower percentage except for Tyr and Trp having a slightly higher one; in peripheral blood the enzyme activity of the oxidative stress indicator, SOD, declined significantly (P<0.05); the percentage of the stress indicator, MDA, increased (P>0.05); the enzyme activity of GT increased extremely significantly (P<0.01); the enzyme activity of GPT and GOP increased plainly or extremely significantly(P>0.05, P<0.01); the enzyme activity of both of CK and LDH increased significantly (P<0.05).The results suggest that long-term feeding with a high concentrate diet causes the organisms in a state of oxidative stress, the distribution and redistribution of amino acids in liver changed, the consumption of amino acids in liver increased, amino acids entering into the mammary gland reduced and the percentage of milk protein declined. Conclusion:A high concentrate diet is adverse to the milk protein synthesis and health of lactating dairy goats.3 The endocrine mechanism and signaling pathway by which a high concentrate diet causes the decrease of milk yield and milk protein contentThe experiment design was the same with that of the second part. Milk samples, jugular blood, liver tissues and mammary gland tissues were taken at the end of each Latin square cycle. The GH and IGF-Ⅰ content in the peripheral blood was determined. Milk yield was measured and milk samples were taken to determine the milk protein and lactose content. Also determined were the GHR, JAK2 and STAT5 gene mRNA expression level in liver and the IGF-Ⅰ R gene mRNA expression level in mammary gland. Results:under the high concentrate diet feeding:in the peripheral blood, the concentration of GH decreased (P >0.05) while that of IGF-Ⅰ decreased significantly (P<0.05); in the liver, the mRNA expression of GHR, JAK2 and STAT5 were down-regulated while that of JAK2 was significantly down-regulated(P<0.05); in the mammary gland, the mRNA expression of IGF-ⅠR was significantly down-regulated(P<0.05). Our results indicate that feeding with a high concentrate diet for a long time cause the decrease of the secretion of endogenous GH, thus inducing the suppression of JAK2-STAT5 pathway. On the one hand, it suppresses the synthesis of milk protein directly. On the other hand, it suppressed the expression of target gene, IGF-Ⅰ. The decrease of the synthesis of IGF-1 in the liver causes the decrease of IGF-Ⅰ content in peripheral blood and naturally lessens the combination of IGF-Ⅰ and its receptor, IGF-1R, which would reduce the galactopoietic effect and the absorption of glucose and ultimately result in a decline in the milk yield.