富含二十二碳六烯酸生物製品之產製與安全性評估 及其對家禽脂質代謝和基因表現之影響

Abstract

Schizochytrium limacinum SR21 (SR21) 是一能產生高量二十二碳六烯酸 (docosahexaenoic acid, DHA) 之海洋真菌，其DHA佔細胞中總脂肪酸之32.7%。因此可做為家禽飼糧之另一DHA補充來源。本試驗在探討飼糧中添加SR21菌粉對蛋黃與肌肉組織中DHA含量及肝臟中脂質生成相關基因表現之影響。並評估其做為蛋雞飼糧添加物之安全性。 試驗一：SR21菌生產DHA之最適培養基組成為：5.0%葡萄糖，2.0%海鹽及1.0%酵母萃取物。其DHA產量可達874 mg/L。將凍乾SR21菌粉分別添加1及3%於飼糧中餵飼白色來航產蛋雞三週，結果顯示菌粉添加不影響產蛋率、蛋重及蛋黃重。1或3%菌粉處理可使蛋黃DHA含量由佔總脂肪酸之0.36%分別增加至1.17%及1.81%。飼糧添加菌粉不影響蛋雞肝臟中脂質生成相關基因之表現。 試驗二：SR21菌粉分別添加1及3%於飼糧中餵飼白色肉雞三週，結果顯示3%菌粉處理組可促進肉雞生長性能並能降低血漿中三酸甘油酯含量，由126.03 mg/dL降低至118.88 mg/dL。1%菌粉處理組可降低肝臟中總脂質含量，由114 mg/g降低至92 mg/g，顯示菌粉中之DHA會影響肉雞體內脂質之代謝。3%菌粉處理可使胸肉中DHA含量由佔總脂肪酸之2.48%增加至7.50%。飼糧添加3%菌粉或1%DHA藻油會降低肉雞肝臟中固醇調節因子結合蛋白1 (sterol regulatory element binding protein 1, SREBP1)、乙醯基輔酶A羧化酶 (acetyl-CoA carboxylase, ACC)、脂肪酸合成酶 (fatty acid synthase, FAS) 及蘋果酸酶 (malic enzyme) 等基因的表現。顯示飼糧之DHA會抑制肉雞脂質生成相關基因的表現。 試驗三：以等氮飼糧餵飼肉雞三週發現，1或3%菌粉處理不會改善肉雞生長性能。將各組肉雞改餵飼對照組飼糧兩週，發現1或3%菌粉處理組之雞隻肝臟及胸肉中DHA含量仍顯著高於對照組，顯示DHA可在肝臟及胸肉中留存至少兩週。各組肉雞改餵飼對照組飼糧兩週後，雞隻肝臟中脂質生成相關基因的表現在各組之間無顯著差異。 試驗四：SR21菌粉分別添加3%、6%及12%於飼糧中餵飼蛋雞六週以評估菌粉的安全性。各處理組之產蛋率、蛋孵化率及血清肝腎功能生化指標值無顯著差異。組織病理分析顯示心、肝、腎及脾等臟器代表病變之樣本數百分比，各處理組之間無顯著差異。顯示SR21菌粉在六週餵飼期間不影響蛋雞繁殖及肝腎功能。 綜上結果顯示，SR21菌粉中之DHA可被雞隻消化吸收並累積於蛋或雞肉中。此種效果有利於生產富含DHA之機能蛋或雞肉。飼糧中DHA能抑制肉雞肝臟中脂質生成相關基因的表現。此種SR21菌粉在六週期間可安全的使用做為蛋雞飼糧添加物。

Schizochytrium limacinum SR21 (SR21) is a marine fungus which can accumulates a high content (32.7% of total fatty acid) of docosahexaenoic acid (DHA) and is a potential candidate for use as a DHA-rich ingredient in poultry diets. In this study, effects of dietary SR21 supplementation on DHA accumulation in the egg or tissues and on mRNA expression of lipogenic genes in livers of laying hens or broilers were examined. The safety of SR21 was also tested to ensure it can been safely utilized as a dietary supplement for laying hens Experiment I : the optimal cultural condition for the DHA production of SR21 was a medium containing 5.0% glucose, 2.0% sea salt, 1.0% yeast extract. The highest DHA productivity of SR21 was 874 mg/L. Using freeze dried SR21 fungal meal (FM) for 3 wk feeding study in laying hen showed that dietary supplementation of 1 and 3% FM did not have an effect on egg production, egg weight and egg yolk weight. The DHA concentration in yolk was increased from 0.36% to 1.17% (1% FM) and 1.81% (3% FM) of total fatty acids. Dietary DHA enrichment had no effect on the mRNA expression of lipogenic genes in the liver of laying hens. Experiment II : the 3 wk feeding trial for broiler showed that dietary supplementation of 3% FM can increase the daily weight gain and feed efficiency. Compared with the control, the 3% FM treatment decreased the content of plasma triacylglyceride (from 126.03 mg/dL to 118.88 mg/dL) while the 1% FM decreased the content of hepatic total lipids (from 114 mg/g to 92 mg/g) suggested the DHA-enriched FM can influence the lipids metabolism in broilers. The 3% FM treatment increased the DHA content of breast muscle from 2.48 to 7.50% of total fatty acids. The mRNA expression of hepatic sterol regulatory element binding protein 1, acetyl coenzyme A carboxylase, fatty acid synthase, and malic enzyme genes were significantly decreased by the supplementation of either 3% FM or 1% DHA oil (P<0.05), suggesting that dietary DHA can inhibit the expression of lipogenic genes. Experiment III : the isoenergetic and isonitrogenic experimental diets were used to study whether dietary SR21 supplementation has the growth-promoting effect in broi8lers. Results showed that feeding broilers with 1 or 3% FM for 3 wk had no significant effect on the growth performances. The broilers were fed the control diet (0% FM) for an 2 extra wk. The data showed tissues except plasma of 1 and 3% FM treatments still contained much higher DHA levels than the control, suggesting a carryover effect of the DHA on the breast muscle and liver tissues. The inhibitory effect of dietary DHA on the mRNA expression of hepatic lipogenic genes was abolished when broilers fed the control diet for 2 wk. Experiment IV : laying hens were fed with 0, 3, 6, and 12% FM diets for 6 wk to evaluate the safety of the FM. The egg production and hatchability of layers were not significant different among treatments. Serum biochemistry markers included glutamate pyruvate transaminase, glutamate oxaloacetate transaminase, gamma-glutamyl transpeptidase , and creatinine concentrations were not significant different among treatments. Histopathologic evaluation of the tissue biopsies showed the 6-wk dietary 12% SR21 fungal meal treatment did not elevate percentages of samples represented as lesions. These results suggested the dietary SR21 bioproduct was not harmful to the reproduction, liver and kidney functions of laying hens during the 6 wk feeding age. In conclusion, dietary DHA-enriched FM obtained from S. limacinum SR-21 can be digested, absorbed and incorporated into egg or muscle. Such a DHA enrichment is beneficial for the production of the functional DHA-enriched chicken meat or eggs. Dietary DHA can inhibit the lipogenic genes expression in the liver of broilers. The SR21 FM can be used safely as a feed supplement for laying hens at a low level at least 6 weeks.