| Adding polyunsaturated fats(PUFA)to ruminant feed can improve the CLA,DHA and other unsaturated fatty acids of ruminant products,thereby improving human health.Tan sheep is a traditional main sheep breed in Ningxia.It is very important to improve the nutritional value of Tan sheep meat quality.The feeding effects of soybean oil,linseed oil and Schizochytrium sp on growth performance,carcass quality,rumen fermentation index,blood biochemical index and CLA content in tissues of weaned lambs of Tan sheep were studied in five experiments.The changes of fatty acid-related enzymes in tissues and rumen microorganism were detected to reveal the effects of different sources of unsaturated fat on Growth performance,carcass quality,rumen fermentation index,blood biochemical index and CLA content in body tissues and the mechanism of CLA synthesis,and to provide technical methods and theoretical basis for the regulation of meat quality in Tan sheep.In experiment 1,the optimum feeding amount of soybean oil,linseed oil and Schizochytrium sp in Tan sheep diet was studied.Diets with a concentrate to roughage ratio of 50:50 were used as culture substrates.Soybean oil,flax oil and Schizochytrium sp were added to the diets with a proportion of 0%,1%,2%and 3%,respectively.The gas production,pH,NDF,NH3-N,BCP and VFA index at each time point were measured in vitro.The single-factors associative effect index(SFAEI)and multiple-facors associative effect index(MFAEI)were used to calculate the optimal rumen fermentation ratio of Soybean oil,flax oil and Schizochytrium sp.The results showed that the MFAEI of soybean oil,flax oil and Schizochytrium sp of 2%adding proportion was the highest,followed by 3%and 1%.The results showed that 2%was the suitable feeding proportion of soybean oil,flax oil and Schizochytrium sp,respectively.The experiment 2 was conducted to study the effects of PUFA on the growth performance and meat quality of Tan sheep.Forty male Tan sheep,aged about 3 months with similar body weight were randomly divided into four groups,with 10 in each group,single bar feeding.The four groups were control group,soybean oil group,flax oil group and Schizochytrium sp group.The addition of soybean oil,flax oil and Schizochytrium sp were 2%of the dry matter in the diet,the concentrate-to-roughage ratio was 50:50,and the feeding period was 60 days.The results showed that the ADG of Tan sheep in each group was more than 150 g.There was no difference(P>0.05)in DMI,carcass weight,net meat weight,tail fat weight,bone-meat ratio,slaughter rate,GR,eye muscle area,water holding capacity,cooked meat rate,pH,marble grain,drip loss 45 min,drip loss 24 h,meat color a,meat color b,meat color L among the three treatment groups and the control group,which indicated that the proportion of adding PUFA was suitable.There was no negative effect on the growth performance and meat quality of Tan sheep.In experiment 3,the effects of PUFA on fatty acids content in Tan sheep tissues were studied.On the day before slaughter,rumen fluid and plasma were taken from each group.The longissimus dorsi muscle and subcutaneous fat of Tan sheep were collected after slaughter.Fatty acid content of thoes samples was tested.The effects of linoleic acid,linolenic acid and docosahexaenoic acid on the synthesis of CLA and n-3 PUFA in Tan sheep were analysised.The results showed that the contents of c9,t11 CLA in muscle tissue of soybean oil group,flax oil group and Schizochytrium sp group increased(P<0.05),C18:1 t-11(TVA)increased significantly(P<0.01),and DHA in muscle tissue of flax oil group and Schizochytrium sp group increased significantly(P<0.01).The contents of c9,t11 CLA in subcutaneous fat of soybean oil group,flax oil group and Schizochytrium sp group increased(P<0.05),TVA increased significantly(P<0.01),and t10,c12 CLA had little difference(P=0.078).The DHA of subcutaneous fat increased significantly(P<0.01),which indicated that feeding 2%linseed oil and Schizochytrium sp could increase the DHA content of lamb muscle and adipose tissue,feeding 2%soybean oil,linseed oil and Schizochytrium sp could increase TVA and c9,t11 CLA of lamb muscle and adipose tissue.The plasma levels of c9,t11 CLA,t10,c12 CLA and TVA in soybean oil group,flax oil group and Schizochytrium sp group increased significantly(P<0.01),while C18:0 in flax oil group and soybean oil group increased significantly(P<0.01),and C18:0 in Schizochytrium sp group decreased significantly(P<0.01).The results showed that the rumen biohydrogenation of docosahexaenoic acid was different from that of linoleic acid and linolenic acid.The levels of c9,t11 CLA,tl 0,c12 CLA and TVA in rumen fluid of soybean oil group,linseed oil group and Schizochytrium sp group increased significantly(P<0.01),which indicated that there were microorganisms producing c9,t11 CLA and t10,c12 CLA in rumen fluid,which were important pathways of c9,t11 CLA production in vivo.The contents of TVA and c9,t11 CLA in rumen fluid,plasma,subcutaneous fat,longissimus dorsi muscle of the four experimental groups showed the same order.The results showed that the production of CLA by Schizochytrium sp was the highest,followed by soybean oil and linseed oil.This study found that there was a strong correlation between TVA and c9,t11 CLA of longissimus dorsi muscle and subcutaneous fat in treatment group.TVA,c9,t11 CLA of rumen fluid had a strong correlation with c9,tl 1 CLA of subcutaneous fat separately.The results showed that the contents of c9,t11 CLA in Tan sheep may be product from two sources:one is the production of c9,t11 CLA by rumen biohydrogenation,the other is the absorption of TVA into the body through endogenous enzymes to produce c9,t11 CLA,which deposited in fat and muscle tissues then.In experiment 4,the effect of feeding PUFA on CLA metabolism pathway in Tan sheep.Serum samples,longissimus dorsi muscle,subcutaneous fat and liver tissues were collected.The indexes of serum,FAS,LPL,SCD and ACC were measured to study the effects of PUFA on the body and the mechanism of CLA synthesis in vivo.The results showed that insulin decreased significantly(P<0.05)and LEP increased significantly(P<0.05)after feeding soybean oil,flax oil and Schizochytrium sp,indicate that the metabolism of PUFA was related to insulin and LEP.Feeding linoleic acid and linolenic acid could increase NEFA,TG,LDL and HDL content in serum(P<0.05),while feeding Schizochytrium sp could decreased NEFA,TG,LDL and HDL slightly(P>0.05),indicate that there was a great difference in metabolism among docosahexaenoic acid,linoleic acid and linolenic acid,and Schizochytrium sp was more beneficial to health than soybean oil and flax oil.Feeding soybean oil,flax oil and Schizochytrium sp could increase MDA content of serum significantly(P<0.05),but SOD,CAT and GSH-Px had little change(P>0.05).The results showed that the addition of linoleic acid,linolenic acid and docosahexaenoic acid had little effect on the activity of antioxidant enzymes in Tan sheep,but had some damage to lipid peroxidation of body tissues.The SCD content of liver tissue in soybean oil group,flax oil group and Schizochytrium sp group decreased significantly(P<0.05),but there was no difference in FAS,ACC and LPL(P>0.05).There was no difference in muscle tissue,subcutaneous fat,LPL,SCD,ACC and FAS among soybean oil group,flaxseed oil group and Schizochytrium sp group(P>0.05).The results showed that the production of c9,t11 CLA in the tissues of Tan sheep feeding PUFA was related to the expression of SCD in liver tissues.In experiment 5,the effects of feeding PUFA on rumen metabolism and Macrobe of Tan sheep were studied.On the day before slaughter,rumen fluid of each group was taken to detect bacteria,pH,VFA and NH3-N,then to study the effects of unsaturated fatty acids on rumen metabolism of Tan sheep and the synthesis mechanism of CLA.The results showed that there was no difference in rumen fluid pH among soybean oil group,linseed oil group,Schizochytrium sp group and the control group.The rumen NH3-N concentration was slightly lower than that of the control group(P>0.05).The total VFA was lower than that of the control group(P<0.05),but the molecule ratio of acetic acid,propionic acid and butyric acid did not decrease(P>0.05).The molecule ratio of acetic acid and propionic acid in soybean oil group and linseed oil group did not change(P>0.05),but Schizochytrium sp decreased slightly(P>0.05),the results showed that dietary supplementation of 2%soybean oil,flax oil and Schizochytrium sp separately had little influence on rumen index of lambs.The number of Butyrivibrio,Butyrivibrio fibrisolvens and Pseudobutyrivibrio in the rumen of soybean oil group and flaxseed oil group was higher than that of the control group(P>0.05),indicate that many microorganisms such as Butyrivibrio,Butyrivibrio fibrisolvens and Pseudobutyrivibrio were involved in the synthesis of c9,t11 CLA from linoleic acid and linolenic acid.Biohydrogenation in the rumen was an important pathway for the synthesis of c9,t11 CLA in lambs.Butyrivibrio,Butyrivibrio fibrisolvens,Pseudobutyrivibrio in Schizochytrium sp group had no significant difference from the control group(P>0.05),which indicate that the microorganisms involved in the rumen biohydrogenation of docosahexaenoic acid in Tan sheep were quite different from those of linoleic acid and flax oil,and there might be specific Macrobes involved in biohydrogenation of docosahexaenoic acid in Tan sheep.In conclusion,the diet adding with 2%soybean oil,flax oil and Schizochytrium sp separately had no bad effects on the growth performance,slaughter performance and meat quality of Tan sheep lambs,and had little influence on most of the rumen fermentation indexes,could improve blood oxidation reaction.Adding 2%soybean oil,linseed oil and Schizochytrium sp separately in diet could significantly improve TVA and c9,t11 CLA content of longissimus dorsi muscle,subcutaneous fat,plasma and rumen fluid,and the best effect was Schizochytrium sp,followed by soybean oil and finally flax oil.In addition,Schizochytrium sp and flax oil could increase the DHA of subcutaneous fat and longissimus dorsi muscle significantly,and improve the value of n-6 polyunsaturated fatty acids in mutton.The SCD of liver tissue in soybean oil group,linseed oil group and Schizochytrium sp group decreased significantly,indicate that CLA in lamb tissue could be synthesized through SCD pathway.Butyrivibrio,Butyrivibrio Fibrisolvens,Pseudobutyrivibrio and other microorganisms in the rumen participate in the synthesis of c9,t11 CLA,but the biohydrogenation pathway of docosahexaenoic acid in the rumen of lambs is different from that of linoleic acid and flax oil. |
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