Effects Of α-Linolenic Acid On Lipid Metabolism And Cholesterol Deposition In Yolk Of Laying Hens

Effects ofα-Linolenic Acid on Lipid Metabolism and Cholesterol Deposition in Yolk of Laying HensTo explore the role ofα-linolenic acid on regulating lipid metabolism, cholesterol deposition effects and the possible mechanism, the current trials were designed to determine the effects ofα-linolenic acid on performance, blood and organ lipid effects, cholesterol content in yolk, endocrine hormone and the relative enzymes' activities and mRNA expression. Results of this study will provide further data for recognizing the effects and regulations of lipid metabolism and cholesterol deposition in laying hens.Experiment 1, The effects ofα-linolenie acid in diets on laying performance aria the lipid content of yolks in laying hensIn this study, a single-factorial design was employed to determine the effects of supplementingα-linolenic acid in diet on laying performance and egg quality in laying hens. The level ofα-linolenic acid was 0.0%(the control group),0.5%, 1.0%,2.0%,3.0% and 4.0%,respectively. The trial period was 28 days. The results showed that compared to control group, 3.0% or 4.0%α-linolenic acid supplementation increased the egg weight (p＜0.05) and decreased the ratio of feed intake to egg production (p＜0.01) . The yolk contents of C18:2, C18:3, C20:5 and C22:6 were significantly increased, while SFA and n-6/n-3 in yolk was significantly decreased in 4th week (p＜0.05or p＜0.01) for linolenic acid supplementation treatments. TG and TC in yolk were decreased at 1.0%α-linolenic acid level(p＜0.05 or p＜0.01). It is concluded that 1.0%-4.0%α-linolenic acid supplementation could improve laying performance and egg quality, depress TG and TC contents and enhance PUFA content in yolk.Experiment 2, The effects ofα-linolenie acid on the content of blood and organ lipids in laying hensBased on the first experiment, the content of blood and organ lipids in laying hens was determined in this experiment. The results showed that blood TG, TC and VLDL-C in the 4th week were quadraticly decreased with increasedα-linolenic acid level(p＜0.05). 4.19％, 4.19％or 4.26％ALA addition may be the optimium level for blood indexes,respectively. The content of TG in middle-size follicle and big-size follicle were significantly decreased (p＜0.01) .The lowest content of TC in middle-size follicle was observed with 2.0% ALA addition. TG and TC contents in the liver were significantly decreased at 1.0% and 3.0%ALA level respectively(p＜0.01). It is concluded thatα-linolenic acid supplementation could decrease TG and TC contents in the blood, follicles and liver.Experiment 3, Methodological study on the determination of triglyceride secretion by using Triton WR-1339 in laying hensTriton WR-1339(TWR), a nonionic detergent, could block the hydrolysis of plasma lipoprotein lipase (LPL) and is widely used to evaluate the hepatic TG secretion in laboratory animals. The objective of this study was to establish the methodology of determining blood TG secretion by investigating the effect of different administration doses of TWR on plasma TG concentrations. Fifteen 24-weeks-old, 1.5kg body weight laying hens were used in a single factorial design with 5 days adaptation period and 2 sample-collection days. Hens were injected from jugular vein with 0 (saline),100,200,300 and 400 mg TWR / kg of body weight as a 4ml solution in saline. Blood samples were taken prior to and 0.5,1,2,4,8,12,24, 36 and 48 hours after TWR injection for determination of plasma TG concentrations. Hens had higher plasma TG concentrations when injected with TWR than with saline beginning from 8 hours after injection(p＜0.05). TG concentrations were kept linear increase until 8 hours post injection for hens receiving 100, 200,300 and 400 mg/ kg respectively, and thereafter decreased. Based on the linear equations, it was calculated that rate of TG secretion(i.e.entry into the circulation) was 0.1216 mmol/(min·kg) of body weight. TWR injection dose had influence on the accuracy of the value of TG secretion rate. It is concluded that intravenous administration of TWR 200～300mg/kg body weight provides a valuable tool for studying blood TG secretion rate in laying hens.Experiment 4, The effects ofα-linolenic acid in diet on the lipid synthesis and secretion in laying hensThe objective of this study is to explore the effects of supplementingα-linolenic acid in diet on the performance, blood TG secretion and enzymes' activities in laying hens. The level ofα-linolenic acid was 0.0%(the control group) or 4.0%. Each group had 5 replications with 10 hens of 24 weeks old per replicate. The trial period was 14 days. The results showed that the performance and yolk TC were improved with supplemented α-linolenic acid. The content of TG and fatty acid synthetase activity in the liver were decreased significantly (p＜0.01). The contents of serum TG and VLDLy were lower (p＜0.01 ). The rate of blood TG secretion(entry) was decreased by 9.40%. The plasma lipoprotein lipase after injection heparin was increased significantly (p＜0.01) . It is concluded that 4.0%α-linolenic acid supplementation could decrease the yolk cholesterol by supressing the lipid synthesis and secretion and promoting peripheral utilization of VLDL.Experiment 5, The mechanism ofα-linolenie acid for regulating lipd metabolism in laying henBased on the 2nd and 4th experiment, the effects of supplementingα-linolenic acid in diet on the hormone,apoB, enzyme activities and mRNA expressions in laying hens were studied to explore the possible mechanism ofα-linolenic acid for regulating lipd metabolism. The results showed that the serum insulin of the trail group was increased significantly (p＜0.01). The serum estradiol was significantly increased in the 2st week compared to the control (p＜0.05). The serum apoB was decreased (p＜0.01). ApoB in the liver was higher than the control group (p＜0.01).AMPK activity was increased with 1.0% level being significantly higher than the control group(P＜0.01).ACC and HMGR activities were significantly decreased (p＜0.05 or p＜0.01). ACC mRNA and HMGR mRNA were decreased and ACC mRNA was decreased significantly. It is concluded that the mechanism ofα-linolenic acid to regulate the metabolism of lipids was associated with the changes of endocrine hormones, related enzymes' activities and enzyme gene mRNA expressions, and apoB synthesis.These studies show thatα-linolenic acid can improve performance,depress the liver lipid synthesis and secretion, lower the blood lipid content, increase the n-3 PUFA content, and decrease the yolk cholesterol content. The mechanism ofα-linolenic acid may be associated with the changes of endocrine hormones, related enzymes' activities and the expressions of enzyme genes.