Effect Of Different Forage Ratio Diets On Milk Fat/Milk Protein And Its Mechanism In Lactating Goats

The purpose of this study was to study the effect of different forage ratio diets on milk fat/milk protein and its mechanism in lactating goats. The research consists of three parts:1Effect of different forage ratio diets on milk protein content and the metabolism flows of free amino acids to milk protein synthesis in lactating goats7healthy mid-lactating goats were used in the study. Goats were randomly divided into two groups, using2×2Latin square design with two replications and each term feeding two weeks. Diet forage to concentrate ratios were4:6(low concentrate group) and6:4(high-concentrate group). Their plasma were obtained from the jugular vein fistula, and milk samples were collected by hand milking. Total protein concentration in milk was determined. The content of free amino acids of plasma and milk from all goats were detected by RP-HPLC. We also detected the contents of the following indicators by automatic blood analyzer, Which were total protein, albumin, globulin, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, creatine kinase, urea, creatinine and uric acid. The results showed that14kinds of free amino acids were isolated from plasma and8kinds of free amino acids were detected from milk in two different diet groups. Amino acid composition of the blood or milk of the lactating goats between two groups fed different crude feed ratio was no obvious difference. Except Ala. all Free amino acids in the blood was higher than the content of the same amino acids in milk. In high concentrate diet group the contents of ketogenic amino acids (Leu, Lys), the branched chain amino acids (He, Leu, and Val) and some glucogenic amino acids (Asn, Ser Gln, Gly, Ala) in blood were lower than these in low concentrate group; He and Leu were significantly reduced (P<0.05). the contents of total essential amino acids and total non-essential amino acid in blood also were both lower than these in low concentrate group. Daily milk yield and total protein concentration in high concentrate group little changed compared with the low concentrate group (P>0.05). The levels of LDH and GPT in plasma in high concentrate group were significantly higher than these in low concentrate group (P<0.05), but other nitrogen indexes had no significant changes. The results suggested that The lactating goats which fed high concentrate diets had a low content of free amino acid for milk protein synthesis, and the contents of LDH and GPT were significantly increased. These different changes might affect the synthesis of milk proteins.2Effects of different forage ratio diets on milk fat content and its precursors in the lactating goatsThe experiment design was the same to the above study, milk production and milk fat content were measured. the contents of non-esterified fatty acids and TG in plasma and milk in goats also were detected by kit method. Glucose, TG, glycerol, HDL-C, LDL-C, lipase in plasma were detected by automatic blood analyzer. The results showed that the level of TG in milk in the high concentrate group was significantly decreased (P<0.05), and its NEFA level was very significantly decreased (P<0.01) compared with the low concentrate group; but milk yield increased a little. The contents of GS, TG, HDL-C in plasma in high concentrate group were higher than these in low concentrate group, but there were no difference (P>0.05). In high concentrate group, the levels of NEFA, glycerol, HDL-C from plasma were significantly increased (P<0.05); The lipase content of plasma was lower than that in low concentrate group, but there was no significant difference (P>0.05). The results suggested that the lactating goats fed high concentrate diets had high NEFA and glycerol levels in their blood, and may have high energy metabolism in their body. This may lead to excessive consumption of milk fat precursors and reduced the production of milk fat because of the less milk fat precursors.3Preliminary study of the mechanism on milk fat/milk protein synthesis of the lactating goats fed high concentrate dietThe experiment design was the same to the above study, all experimental goats were installed Ruminal cannulas after the adaptation period, Their liver samples also were collected by living donor liver biopsy in the end of each cycle. Ruminal liquid samples were taken from the ventral sac of the rumen before feed and at1,2,4,6,10h after the morning feeding for2days at the end of each period. The pH of the rumen fluid was immediately determined by means of a portable pH meter. The total liver proteins of two groups were extracted and separated by the two-dimensional electrophoresis (2-DE) method. The levels of prolactin, glucagon, Growth hormone, insulin, insulin-like growth factor-1, leptin were detected by ELISA or RIA method. Results1) The pH value of rumen was significantly lower in high concentrate group and the duration of pH less than5.8was greater than4h (P<0.05), so the goat rumen in high concentrate group was in the subacute acidosis state (SARA);2)34protein spots of more than3-fold difference in both groups were revealed by PDQuest7.1and MAIDI-TOF-TOF, and of which15were identified. These proteins which were identified mainly related to metabolism and energy transfer. The results indicated that glucose, lipid and protein catabolism could be enhanced and gluconeogenesis was blocked and anti-oxidative stress was strengthened in liver of lactating goats fed high concentrate diet.3) The content of Insulin in high concentrate group was significantly higher (P<0.05), and that of IGF-1were just opposite (P<0.05); Compared with the low-concentrate group, the contents of Leptin, PRL, GC and GH from plasma of the high concentrate group goats were a little higher, but there was no significant difference(P>0.05). We found that the lactating goats were fed with high concentrate diet, the subacute ruminal acidosis(SARA) would be reduced in their rumen. So the level of energy metabolism of these goats was enhanced and resulted in the changes of metabolism in liver, which catabolism of fatty acids, sugars and amino acids in liver all were enhanced. It prompted that carbohydrate, lipid and amine acid in the liver mainly participated in oxidation and energy supply when SARA occurred. So the excessive consumption of the precursor of milk in liver lead to milk protein and milk fat decreased. Hormones were involved in the regulation of milk fat/milk protein synthesis process; GH-IGF-I axis and insulin/glucagon axis were mainly pathway.