Studies On The Effects Of Feeding High Grain Diets To Lactating Dairy Goat On Lactation Performance

In order to maximize energy intake and support high milk production or rapid growth,current intensive production systems for ruminants commonly feed large amounts of grain diets to ruminant animals,which might be useful to lower the cost and obtain higher economic profits during a short period.However,the excessive amounts of non-structural carbohydrates and highly fermentable forages will lead to a rapid fermentation and organic acids accumulation in rumen,and likely induces subacute ruminal acidosis(SARA)disease.Both cute ruminal acidosis and subacute ruminal acidosis can cause milk fat depression and also lead to the shift of fatty acids profiles in lactating cows.Current research mainly focused on the effects of short-term high concentrate diet feeding on lactation performance in lactating dairy cows.There were few reports on the effects of long term feeding of high concentrate diets on lactation performance and milk quality in lactating dairy cows.Therefore,in the present study,we investigated the effects of short-and long-terms feeding high concentrate diet to lactating dairy goats on blood hematological parameters,body oxidative stress,milk production and milk quality,and particularly focused on lipids and protein synthesis and the relative mechanism in the mammary gland.1.Effects of feeding high grain diets on the hematological parameters and oxidative stress in dairy goatTo investigate the effect of feeding a high concentrate diet to lactating dairy goats on the lactation performance,body healthy status,the structure and functions of mammary gland,seventeen mid-lactating dairy goats were randomly allocated to 3 groups in this study.One group goats were fed with a low-concentration(CON)diet as the control group(35%concentrate diet,n=5)for 19 wks,and goats were fed with a high concentrate(HC)diet for a long time(19 wks)as HL group(65%concentrate diet,n = 7)or for a short time(4 wks)as HS group(n = 5),respectively.At the end of experiment,samples including milk,blood and mammary gland tissues were collected and analyzed.The results showed that compared to CON group,the liver weight(P<0.01)was significantly increased in HL and HS group;the body weight(P<0.05)was also significantly increased in HL group,and spleen weight(P<0.05)was significantly increased in HS group.However,pH values in the lumen fluids of rumen,omasum,colon and cecum were not changed among three groups.The data of hematological parameters showed that there was no effect of high concentration diet on WBC(white blood cell),while RBC(red blood cell)(P<0.05),HCT(red blood cell specific volume)(P<0.05)and RDW(red blood cell distribution width)(P<0.05)were significantly increased in HL and HS group compared to CON control.Compared to CON,plasma GSH-PX activity(P<0.05)was significantly increased in HL group,and MDA content was significantly decreased in HS group(P<0.05).In mammary gland,CAT activity was moderately increased in HS and HL group compared to control.2.Effects of feeding high grain diets on the fatty acid composition in milk and the milk fat synthesis in mammary glandCompared to CON group,high concentration diet feeding did not alter genes expression involved in the inflammatory response.However,the expression of genes related to cell apoptosis was significantly changed by HC diets feeding in lactating dairy goats.The expression of Caspase-3 gene was markedly up-regulated(0.05<P<0.1))in HS group,and Bcl-2 mRNA expression was significantly down-regulated(P<0.05)in HS group compared to control.The ration of Bax/Bcl-2 genes expression(P<0.05)was also significantly increased in HS and HL group,moreover,the activity of caspase-3 enzyme(P<0.05)was significantly increased in HS group.In addition,the number of SCC(somatic cell count)was also increased in HS and HL groups but did not reach the statistical significance.Milk production was significantly increased by feeding HC diet in both HS and HL group compared to CON(P<0.01),while the percentage of milk fat was significantly decreased in HL but not in HS group(P<0.05).The total amount of saturated fatty acids in milk was not changed by feeding HC diet,whereas the levels of unsaturated fatty acids(UFA)and monounsaturated fatty acids(MUFA)were markedly decreased in HL group compared to CON(P<0.05).Among these fatty acids,the concentrations of C17:1(P<0.01),C18:1n-9c(P<0.05),and C18:3n-3r(P<0.01)were markedly decreased in HL group,and the concentrations of C14:0(P<0.05),C 20:0(P<0.05),C18:3n-3r(P<0.01)were significantly decreased in HS group compared to CON.However,the concentration of C18:2n-6c(P<0.05)and C20:4n-6(P<0.05)concentrations in milk fat were increased in HS group.Real-time PCR results showed that mRNA expression of genes involved in milk fat production in the mammary gland was generally decreased in HL and HS goats compared to CON.Among these genes,ACSL1,ACSS1&2,ACACA,FAS,SCD,FADS2 and SREBP1 were significantly down-regulated in the mammary gland of HL group(P<0.05),and the expression of ACSS2,ACACA and FADS2 mRNA were markedly decreased in HS goats compared to CON(P<0.05).Contrary to genes expression,the levels of DNA methylation in the promoter regions of ACACA and SCD genes were significantly up-regulated in HL group compared to CON(P<0.05).The levels of ACSL1 protein expression and FAS enzyme activity was also decreased in the mammary gland of HL goats compared to CON(P<0.05).The above results showed that general down-regulation of genes expression involved in milk fat production and higher DNA methylation in mammary gland may contribute to the decrease of milk fat production in HL goats.3.Effects of feeding high grain diets on milk protein,lactose synthesis in mammary glandCompare to CON group,plasma concentration of Tyr,Met,Lys,Glu,His,Arg,Pro,TAA,GAA,NEAA were significantly increased(P<0.05),and the concentrations of Cys,Phe(P<0.05)were significantly decreased in HS group,while the concentration of TAA,NEAA,Met(P<0.05)was significantly increased in HL group.Real-time PCR results showed that mRNA expression of genes involved in milk protein and lactose synthesis were generally decreased in HC group compared to CON group.Among these genes STAT5,mTOR,CSN2,GLUT1,HK and AKT1 mRNA expression(P<0.05)were significantly down-regulated in the mammary gland of HL group.Moreover,the levels of PS6K/S6K,P-AKT/AKT,Glut4 protein expression and HK enzyme activity were all down-regulated in the mammary gland of HL goats compared to CON.