| The influence of a single amino acid supply on milk protein synthesis is not a simple and direct mass effect,but a complex process mediated by intracellular signal pathways,endocrin e pathways and substrate effects.Different essential amino acids(EAA)have various characte ristics.The development of precise amino acid nutrition technology for lactating dairy animal s requires in-depth research on these characteristics.The purpose of this project is to observe t he effect of leucine(Leu)gradient supply on mammary gland amino acid metabolism.Four multiparous Laoshan dairy goats were used.The experimental design was a 4 × 4 L atin square.After the test sheep were starved for 24 hours,the jugular vein was perfused with an amino acid mixture prepared according to casein and glucose to meet the energy and protei n needs.The experimental treatment was gradient addition of 0%,30%,60% and 100% Leu,a nd the continuous perfusion for each phase of the test was 9 hours.The milk production in the middle 7 hours was recorded and blood and milk samples were collected,and breast tissue sa mples were collected from the living body.The milk fat content of the 60% group was significantly different from other groups(P=0.02).The milk fat content of each treatment group did not change linearly with the increase o f Leu infusion;the milk protein content increased linearly with the supply,which was close to the trend level(P=0.11);Milk protein production has a linear increase trend(P=0.08),and th ere is no significant difference between the treatment groups;the difference in milk productio n between groups is not significant(P> 0.10),numerically,compared with the 100% group,0The milk production of the %,30%,and 60% groups decreased by 60.67g/7h,34.91g/7h,32.23g/7h,respectively;with the increase of Leu perfusion,the lactose content increased linearly(P<0.05),the 60% group There was a significant difference from the 0% and 100% groups(P=0.03);the milk protein content of the complete deletion group was 12% lower than that of th e 100% group,and there was no significant change in the other groups.The concentration of Leu in plasma increased linearly with the increase of Leu perfusion(P<0.001).When Leu was completely absent,the Leu concentration in arteries and veins was 27% and 18% of 100%.W ith the increase of Leu supply,the breast affinity of Leu decreases,and the clearance rate of L eu decreases(P<0.01).The blood flow decreased linearly(P<0.01).The blood flow of the0%,30%,and 60% group was 122%,75%,and 57% higher than that of the 100% group,resp ectively.The increase in blood flow partially offset the negative effects of low Leu supply,an d the amount of Leu extracted did not change significantly(P=0.93).Plasma IGF-1 increased linearly with the increase of Leu perfusion(P<0.05),and glucagon decreased linearly(P<0.05).The concentration of IGF-1 in the complete deletion group decreased by 13%.Glucagon b etween treatment groups,Insulin,growth hormone,etc.There are no significant differences.With the increase of Leu perfusion,the phosphorylation levels of e IF2ɑ,P70S6K1 and 4EBP1 were not significantly different(P>0.10).These results indicate that under the short-term low supply of Leu,the breast increases the blood flow to increase the affinity of Leu to maintain t he Leu extraction as much as possible to maintain the balance.Different concentrations of Le u have different effects on the synthesis of milk protein(P=0.11),Different concentrations of Leu have different effects on lactose synthesis(P=0.03),and different concentrations of Leu have different effects on milk fat synthesis(P=0.02).Different concentrations of Leu have dif ferent effects on the production of breast milk.The amino acid composition of the 60% group in this experiment is more conducive to the synthesis of milk fat,but not conducive to the synt hesis of lactose.When the body faces Leu loss,the antagonism between BCAAs inhibits milk production,and the antagonism between BCAAs may be different in different concentrations of Leu.This process involves endocrine pathways(mainly glucagon and IGF-1)and substrate regulation. |
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