Effect Of Flaxseed On The Production Of Dairy Cows,Fatty Acid Profile And Flavor In Raw Milk

ω-3 polyunsaturated fatty acids（n-3 PUFA）are essential nutrients for human body as well as playing important roles.In recent years,With the continuous research on milk,the nutrition of milk has been widely recognized by human.Therefore,the development of milk rich in n-3 PUFA is conducive to improving intake of n-3 PUFA and which is good for human’s health.In order to develop milk rich in n-3 PUFA,this study mainly design 2 experiments:Experiment 1.Effect of flaxseed supplementation on performance,milk and plasma fatty acid composition,rumen metabolism of dairy cows.Experiment 2.Effect of flaxseed supplementation on the composition of volatile organic compounds in raw milk.Experiment 1.Effect of flaxseed supplementation on performance,milk and plasma fatty acid composition,rumen metabolism of dairy cowsThis part includes 3 experiments:1)Effect of flaxseed supplementation on performance,milk and plasma fatty acid composition of dairy cows;2)Effect of flaxseed supplementation on rumen metabolism of dairy cows;3)Study on rumen biohydrogenation ofα-linolenic acid in vitro1)Effect of flaxseed supplementation on performance,milk and plasma fatty acid composition of dairy cowsThe aim of this experiment was to investigate the effects of whole and ground flaxseed on the production performance,fatty acid composition in plasma and raw milk,especially n-3PUFA.Thirty Holstein cows（lactation days:90±28 days,body weight:628±103 kg）were randomly divided into three groups.The three groups of cows were fed a diet without flaxseed（CK group）,a diet with whole flaxseed（WF group;1500 g whole flaxseed per day）and a diet with ground flaxseed（GF group;1500 g ground flaxseed per day）respectively.Results showed that there were no significantly differences in dry matter intake（DMI）,milk yield,energy corrected milk（ECM）and 4%fat corrected milk（4%FCM）between the treatments（p>0.05）.For milk content,there was only significant difference showed in milk protein content between CK group and WF group（p<0.05）,but there was no significan t difference in milk protein yield（p>0.05）.In addition,the content and yield of other milk components（including milk fat,lactose,non-full-fat milk solids and full-fat milk solids）were not significantly different between the treatments（p>0.05）.Compared with CK group,ALA,Eicosatrienoic acid（ETE,C20:3 cis-11,cis-14,cis-17）,and Eicosapentaenoic acid（EPA,C20:5 cis-5,cis-8,cis-11,cis-14,cis-17）in plasma and raw milk of WF and GF groups were significantly higher（p<0.05）.Compared with CK group,ALA production in WF group and GF group increased to 232%and 360%respectively.Compared with WF group,ground flaxseed supplementation in diet could improve the efficiency of ALA transpor t to milk.The content of Docosahexaenoic acid（DHA,C22:6 cis-4,cis-7,cis-10,cis-13,cis-16,cis-19）in raw milk of GF group was higher than that of CK and WF group（p<0.05）.However,there was no significant difference in plasma DHA between the treatment groups.The content of total n-3 PUFA in plasma and raw milk was significantly higher in WF and GF groups than that in CK group,and the content of GF group was the highest.In general,compared with CK group,the addition of intact and ground flaxseed increased the levels of n-3 PUFA and total n-3PUFA in milk and blood,and decreased the ratio ofω-6 polyunsaturated fatty acids（n-6PUFA）to n-3 PUFA.Compared with WF group,the ground flaxseed supplementation in diet could increase the content of ALA in milk and im prove the efficiency of ALA transport from the diet to milk.In addition,there was no significant difference in plasma biochemical indexes between different treatment groups（p>0.05）,indicating that the addition of whole and ground flaxseed had no effect on the health of dairy cows.2)Effect of flaxseed supplementation on rumen metabolism of dairy cowsThe main of this study was to explore the effects of whole and ground flaxseed supplementation in diet on rumen metabolism of dairy cows.Results of this experiment showed that the highest content of ALA in rumen fluid found in WF group（p<0.05）,however no significant difference showed between CK group and GF group（p>0.05）.The p H value and ammonia nitrogen（NH₃-N）in rumen had no significant difference between the treatments（p>0.05）.The molar ratio of volatile fatty acids（VFA）was significantly different between the treatments.Compared with CK group,the molar ratio of acetic acid increased in WF and GF group,and was the highest in GF group（p<0.05）.The molar ratios of propionic acid,isobutyric acid,butyric acid,isoval eric acid and valeric acid also had significant differences between the treatments（p<0.05）,and showed the same trend among the three groups（CK group<WF group<GF group）.Rumen microorganisms are the main reason influencing VFA in rumen.This experiment found that the main biohydrogenation bacteria Ruminococcaceae＿NK4A214＿group was significant difference in rumen between the treatments（p<0.05）,and the trend was CK group<WF group<GF group.The abundance of Christensenellaceae＿R-7＿group and Eubacterium＿coprostanoligenes＿group also had significant differences between the treatments（p<0.05）.And the abundance of group bacteria had the same trend among the three groups:CK group<WF group<GF group.Compared with ground flaxseed,the flaxseed shell leads to the direct excretion of most whole flaxseeds,which reduces the release of ALA in rumen.In general,the ALA release of flaxseed treated in different ways wa s different in rumen.However,the molar ratio of volatile fatty acids and bacterial abundance may be mainly affected by the release of ALA in rumen.3)Study on rumen biohydrogenation ofα-linolenic acid in vitroOur studies found that the C18:3 trans-9,cis-12,cis-15,isomer of ALA,can be detected in milk.This isomer in milk may transport from the products of rumen biological hydrogenation of ALA,but there is no report.The main purpose of this study is to explore whether C18:3 trans-9,cis-12,cis-15 is the biological hydrogenation products of ALA in rumen,and investigate the possible biological hydrogenation pathway of ALA.This study may provide a theoretical basis for further understanding the ALA biohydrogenation in rumen.The in vitro test included two treatments,one was the control group（CON group）added 50μL ethanol,the other is ALA group added 50μL ethanol and ALA 2.6 Mg（ALA addition is calculated as 1.30%of the dry matter basis of the diet）.The experiment chose 80fermentation bottles,40 in each group,and set 8 time points of 0,0.5,1,2,3,4,5 and 6 h,with 5 repetitions at each time point.The composition of C18 fatty acids in each bottle was analyzed after fermentation.Results showed that C18:3 trans-9,cis-12,cis-15 was not detected in CON group,but C18:3 trans-9,cis-12,cis-15 could be detected in fermentation fluid after adding ALA.After fermentation for 1 h,the contents of C18:3 trans-9,cis-12,cis-15 reached the peak,and then decreased gradually.C18:3 trans-9,cis-12,cis-15 was not detected in CON group during the whole experiment period.Thus,the ALA could convert to C18:3 trans-9,cis-12,cis-15 by biohydrogenation in rumen.The addition of ALA could also increase the contents of C18:2 trans-9,cis-12,C18:2 cis-9,trans-11,C18:1 cis-12,C18:1 tran-11,C18:1trans-9 and C18:1 cis-6 in fermentation fluid.This study concluded that C18:3 trans-9,cis-12and cis-15 is the intermediate products of rumen bio hydrogenation of ALA.It is speculated that there may be biohydrogenation pathways in rumen:ALA→C18:3 trans-9,cis-12,cis-15→C18:2 trans-9,cis-12→C18:1 cis-12/C18:1 trans-11/C18:1 trans-9→C18:0Experiment 3.Effect of flaxseed supplementation on the composition of volatile organic compounds in raw milkThe volatile organic compounds of raw milk were determined by headspace gas chromatography ion mobility spectroscopy（HS-GC-IMS）.The results showed that 40 volatile organic compounds were identified in all raw milk samples,including 3 acids,6 esters,11aldehydes,7 alcohols and 13 ketones.Ground flaxseed supplementation in diet could influence 5 types of volatile organic compounds in raw milk.However,whole flaxseed supplementation could influence 22 compounds.Whole flaxseed supplementation in diet can increase the concentration of nonanal,heptanaldehyde and hexanal in raw milk,and reduce the concentration of caproic acid（monomer;M）,2-Hexanol,ethanol（M）,2-heptanone（dimer;D）,2-pentanone（M）,2-pentanone（D）and 3-hydroxy-2-butanone（M）.ground flaxseed supplementation in the diet could reduce the contents of 2-pentanone（M）and 2-pentanone（D）in raw milk,but could increase the content of propyl acetate which could provied fruit flavor in milk.In addition,principal component analysis（PCA）based on t he identified volatile organic compounds signal strength shows that raw milk in CK group and WF group can be distinguished,but raw milk in GF group and CK group cannot be distinguished.In general,compared with the raw milk of GF group,the addition of whole flaxseed to the dairy cow’s diet will increase the fishy（heptanal）cardboard-like（pentanal）flavor,and reduce the sweetness（hexanoic acid,2-heptanone）and fruit flavor（ethyl butyrate,ethyl caproate,2-heptanone）.These changes may reduce human’s acceptance of the milk.The addition of ground flaxseed has less effect on the flavor of raw milk,and c an increase the fruit flavor（propyl acetate）in milk.Based on the above results,this experiment found that 1500 g whole and ground flaxseed per day could increase the content of ALA and n-3 PUFA in milk and improve the composition of fatty acids in milk.And had no influence on the health and production of dairy cows.Feeding flaxseed can change the composition of bacteria in rumen and the fermentation mode to propionic acid type.Compared with whole flaxseed,ground flaxseed supplementation in diet showed more efficiency on the increase of n-3 PUFA content in milk,and had less effect on volatile organic compounds in the obtained raw milk rich in n-3 PUFA.This study may provide theoretical basics for the production of milk rich in n-3 PUFA.