Effects Of Coated Gamma-aminobulyric Acid On Alleviating Heat Stress Of Cows And Investigation On The Mechanism

This study was conducted to evaluate the effects of coated gamma-aminobutyricacid (GABA) in dariy cow under heat stress,and investigate on the related mechanismby immunity、endocrine and antioxidation.Twenty Holsteins lactating cows, offered the same basal diet, were blocked bydays in milk, milk yield and parity and then randomly allocated toⅠof Ⅳ dietarytreatments: negative control (group Ⅰ), groups Ⅱ、Ⅲ、Ⅳ of coated GABAsupplementation (5g/d、10g/d and15g/d),the cows were raised including7days ofpretreating and30days for test.The milk yield was monitored by computer, Rectaltemperature and respiratory rate were measured at the start of the study and after14and29d.The lactose、milk fat、lactoprotein and total milk solid were detected by Milkcomposition analyzer. The serum index were measured as follows: the concentrationof GABA;the levels of CRH, ACTH and Cor; the concentration ofpotassium,sodium,calcium,phosphorus,chloride and HCO3－; the level of MDA, theactivity of SOD and GSH-Px enzyme;the immunity of IL-2,IgG,IgM and IgA;thelevels of T3,T4,GH and INS, the concentration of blood glucose and blood lipid.Theresults showed:(1).Rectal temperature and respiratory rate were lowerd by using coated GABA, Onday-10and30, the rectal temperature of groups Ⅲ、Ⅳ were significantly lower thangroupⅠ(P <0.01), the respiratory rate of group Ⅳ was lower than groupⅠ(P <0.05).(2).GABA concentration in the serum rose as GABA addition in feed increased, Onday-15, the GABA concentration of group Ⅳ was higher than groupⅠ(P <0.05), Onday-30, the GABA concentration of groups Ⅲ、Ⅳ was significantly higher than groupⅠ(P <0.01).(3). Compared with groupⅠ, the addition of coated GABA decreased the hormone ofHPA axis, the CRH level of groups Ⅲ、Ⅳ and Cor level of groups Ⅳ were lower(P <0.05), while the ACTH level of group Ⅳ was significantlydecreased (P <0.01).(4).The concentrations of sodium、calcium、phosphorus、chloride、HCO3－and lipid in the Serum were increased by coated GABA addition, meanwhile, potassiumconcentration was decreased, blood glucose level was fall after rising. Compared withgroupⅠ,on day-15, the sodium concentration of groups Ⅲ、Ⅳ was higher (P <0.05)、(P <0.01), on day-30, the sodium concentration of groups Ⅲ、Ⅳ was higher (P <0.05); on day-30, the potassium concentration of group Ⅳ was lower (P <0.05);on day-15,the calcium concentration of group Ⅳ was higher (P <0.05), On day-30, the calciumand phosphorus concentrations of group Ⅳ were significantly higher (P <0.01).Compared with groupⅠ,On day-15,the blood glucose levels of all test groups wererised,in which, group Ⅳ was significantly changed (P <0.01);However,It was reducedon day-30. On the contrary, the blood lipid levels of all test groups were rised onday-30including gr-oup Ⅳ(P <0.05).(5).The coated GABA enhenced the activity of SOD and GSH-Px, brought down thelevel of MDA. In which, MDA of group Ⅳ was lower on day-15(P <0.05) andsignificantly lower on day-30(P <0.01), groupⅡ and group Ⅲ showed the similarresults on day-30.The activity of GSH-Px in group Ⅳwas increased on day-15and30(P <0.05), meanwhile, group Ⅲ was only increased onday-30(P <0.05). Though theactivity of SOD was rised in test groups, it is no-tsignificant.(6).The concentrations of IL-2、IgA、IgG and IgM in the Serum were increased bycoated GABA addition,including IL-2of group Ⅳ on day-15and30(P <0.05); IgGof group Ⅳ on day-15(P <0.01); IgM of group Ⅲ and Ⅳon day-30(P <0.05).(7).The concentrations of T3、T4and GH in the Serum were increased by coatedGABA addition,with decreased of INS.T3of group Ⅲ on day-15and30washigher(P <0.05), T4of group Ⅲwe arne di nⅣcreased separately(P <0.05)、(P <0.01).On day-15and30, GH of group Ⅳ was changed the same as T4; however, INS wasreduced significantly.(8).The milk yield、milk fat、lactoprotein and total milk solid were rasied in testgroups,but for the lactose.Compared with group Ⅰ,the milk yield and thelactoprotein on day-30of group Ⅳwere increased significantly(P <0.01),furthermore,total milk solid was increased(P <0.05).The milk yield and total milk solid on day-30of group Ⅳ were rasied (P <0.05) and significantly rasied (P <0.01).The results demonstrated that dietary coated GABA prevented HS-related depressionin performance,with a best effect of group Ⅳ.We concluded the possiblemechanism:coated GABA played a role by suppressing HPA axis, enhencing theimmunity and antioxygenic property,keeping the acid-base and ionic balance,regulating the secretion of GH、T3、T4and INS,improving the energy metabolism ofcows.