大豆抗原蛋白对罗氏沼虾生理生化及免疫的影响

Physiological, biochemical, and immune effects of dietary soybean antigen proteins in the giant river prawn(Macrobrachium rosenbergii)

为探讨大豆抗原蛋白与豆粕饲用效果的关系,本研究配制4种等氮等能的实验饲料,以含有21.5%鱼粉、15.45%豆粕和15%发酵豆粕的实用饲料为基础饲料(T15组),用发酵豆粕完全替代T15组中的豆粕(TF组),比较发酵豆粕对豆粕的替代效果;再以鱼粉、酪蛋白和大豆分离蛋白为主要蛋白源分别配制与T15、TF组相近抗原蛋白含量的半纯化饲料AP5、AP0(抗原蛋白含量分别为5%和0%)组,探究抗原蛋白的生物学效应。选用初始体重为(0.17±0.02) g的罗氏沼虾(Macrobrachium rosenbergii)在室内水泥池网箱中进行为期64 d的养殖实验。结果显示:两种系列饲料中,大豆抗原蛋白含量的降低对罗氏沼虾生长、血清生化指标及免疫相关基因表达有不同的影响。在实用饲料组中,随着大豆抗原蛋白的降低,罗氏沼虾的增重率、肝胰腺蛋白酶活力、血清白蛋白、总蛋白、鳃Toll受体mRNA、NF-κB mRNA和肝胰腺HSP70 mRNA相对表达量都显著降低(P<0.05),而血清超氧化物歧化酶活力显著升高(P<0.05);在纯化饲料组中,随着大豆抗原蛋白的降低,罗氏沼虾的增重率、血清超氧化物歧化酶活力和丙二醛含量、肝胰腺HSP70mRNA相对表达量没有显著性差异(P>0.05),肝胰腺淀粉酶活力、蛋白酶活力、血清白蛋白、总蛋白都显著降低(P<0.05),而肌肉粗灰分、血清谷草转氨酶活力、鳃Toll受体mRNA、NF-κBmRNA相对表达量显著升高(P<0.05)。比较实用饲料组与半纯化饲料组的结果可知,罗氏沼虾对实用饲料中5%的大豆抗原蛋白有一定的耐受性,并且有利于其生长和健康,推测大豆抗原蛋白与豆粕中的其他抗营养因子间存在有益的联合效应,显著降低其中的大豆抗原蛋白含量则不利于蛋白合成代谢和肝胰腺健康,导致生长性能下降。建议在实际生产中发酵豆粕和豆粕按一定比例混合使用。

Soybean antigen proteins(soybean glycinin and β-conglycinin) are the main anti-nutritional factors in soybean meal. Recent studies showed that a high level of glycinin and β-conglycinin in soybean meal can disrupt the intestinal tissue structure, resulting in digestion and absorption disorders, stunted growth, and allergic reactions with a variety of non-specific and specific immune responses in aquatic animals. In recent years, fermented soybean meal has been increasingly used in aquatic animal feed. Compared to soybean meal, anti-nutritional factors, particularly soybean antigen proteins in fermented soybean meal, are drastically reduced. This study was conducted to compare the effects of soybean meal(SBM) and fermented soybean meal(FSBM) on the growth,serum biochemical indices, gene expression, and oxidative status in Macrobrachium rosenbergii and evaluate whether the effects were caused by soybean antigen protein. Practical diets(T15, TF) and purified diets(AP0, AP5)were formulated for the feeding trial. Compared to T15(21.5% FM, 15.45% SBM, 15% FSBM), the soybean meal was completely replaced with fermented soybean meal in TF, while AP0 and AP5 were semi-purified diets containing approximately the same content of soybean antigenic protein as TF(nearly 0% soybean antigen proteins)and T15(approximately 5% soybean antigen proteins), respectively, with soybean antigen proteins included as the sole anti-nutritional factor. Giant river prawns with an initial average body weight of(0.17±0.02) g were cultured in net cages in a fixed indoor cement tank and fed the above four diets for 64 days. The results showed that as soybean antigen proteins were reduced, trypsin activity was decreased for both series of diets. The practical diet groups showed a significantly decreased growth rate, while the purified diet groups did not, demonstrating that 5%soybean antigen protein did not affect the growth of M. rosenbergii. In contrast, a significant reduction in soybean antigen protein in the practical diet was not conducive for growth. A certain amount of soybean antigen protein increased trypsin activity to promote digestion of the feed, which in turn had a positive impact on growth. In the practical diet groups, there was no significant difference in the serum malondialdehyde content and expression of nuclear factor-κB mRNA in the gills. Superoxide dismutase activity in the serum was significantly higher in TF,while expression of the Toll-like receptor in the gills and HSP70 mRNA in the hepatopancreas was significantly decreased. In the purified diet groups, there was no significant difference in the serum superoxide dismutase activity, malondialdehyde content, and HSP70 mRNA expression in the hepatopancreas, while expression of the Toll-like receptor and nuclear factor-κB mRNA in the gills was significantly higher in the AP0 group. The results showed that fermented soybean meal scavenged free radicals by synthesizing antioxidant enzymes and reducing oxidative stress in the hepatopancreas, which may not be directly related to the reduction of soybean antigen protein content. Soybean antigen proteins and a variety of anti-nutritional factors together likely stimulate the body’s immune system and promote immunity by decreasing Toll-like receptor and nuclear factor-κB mRNA expression levels. Total protein in the serum was significantly decreased in the practical diet groups, and aspartate aminotransferase activity was significantly increased. However, total protein and albumin levels were significantly decreased in the purified diet groups. The results demonstrated that this concentration of antigen proteins improved the health of the hepatopancreas and the body’s amino acid and protein synthesis metabolism. In addition to a more sensitive immune response, the T15 group showed better growth performance in the practical diet groups.In conclusion, M. rosenbergii was tolerant to 5% of soybean antigen protein, which was beneficial for its growth and health. A synergistic effect between soybean antigen protein and other anti-nutritional factors likely occurred.Low levels of soybean antigen proteins in the feed led to reduced protein synthesis and metabolism in the hepatopancreas and decreased growth. These results suggest that fermented soybean meal and soybean meal can be mixed together in an appropriate proportion under normal feeding conditions.