灭活植物乳杆菌及其代谢物对草鱼生长性能和肠道健康的影响

为评估灭活植物乳杆菌(Lactobacillus plantarum)及其代谢物在草鱼(Ctenopharyngodon idella)饲料中的应用效果，配制4 组分别含0%(对照组)、300、600和900 mg/kg植物乳杆菌及其代谢物 (LPM)的等氮等能饲料，饲喂草鱼幼鱼初始体重：(80.47±1.04) g] 6 周。结果显示，草鱼增重率和饲料效率在LPM添加量为300 mg/kg时分别较对照组显著提高19.09%和8.57%(P＜0.05)。LPM添加组肥满度显著低于对照组，且添加量为900 mg/kg时，脏体比较对照组显著降低18.84%(P＜0.05)。全鱼粗蛋白质含量、饲料蛋白质效率和蛋白质沉积率均在添加量为300 mg/kg达到最大值，分别较对照组显著提高4.40%、11.97%和7.64%(P＜0.05)。LPM添加组肝胰脏和肠道蛋白酶活性较对照组显著升高(P＜0.05)。LPM添加量为600 mg/kg时，草鱼肠道的绒毛数量、绒毛长度和绒毛宽度显著高于对照组 (P<0.05)。饲料中添加LPM对草鱼肠道菌群的多样性无显著影响(P>0.05)。LPM添加量为300 mg/kg时，乳杆菌属和梭菌属的细菌丰度较对照组显著升高(P<0.05)。嗜水气单胞菌、诺卡氏菌、副溶血弧菌对LPM极度敏感。血清总胆固醇、高密度脂蛋白胆固醇、低密度脂蛋白胆固醇的含量随着LPM添加量的增加而增加。LPM 添加组血清总蛋白、白蛋白含量和碱性磷酸酶活性较对照组显著升高(P<0.05)。综上，饲料中添加300~600 mg/kg LPM能够抑制有害菌的繁殖，改善肠道功能，调节免疫功能，保障肝胰脏的正常功能，提高饲料蛋白质利用，进而提高草鱼生长性能。

Effects of inactivated Lactobacillus plantarum and its metabolites on growth performance and intestinal health of grass carp (Ctenopharyngodon idella)

Lactobacillus plantarum is defined as beneficial bacteria via produce lactic acid, short-chain fatty acids, antimicrobial peptides, and other active substances through fermentation, and has probiotic effects such as alleviating oxidative damage to cells, regulating immunity, and promoting growth. However, the use of viable bacteria in aquatic feed is limited due to the prolonged high-temperature environment during the processing of aquatic feed. To investigate the optimal supplementation of dietary inactivated Lactobacillus plantarum and its metabolites (LPM) in grass carp (Ctenopharyngodon idella), fish (initial mean weight: 80.47±1.04 g) were fed four isonitrogenous and isoenergetic diets which were formulated to contain graded LPM levels (0, 300, 600, 900 mg/kg LPM, respectively) for 6 weeks. The results showed that weight gain rate (WGR) and specific growth rate (SGR) showed a trend of first increasing and then decreasing, and the WGR and feed efficiency reached the maximum value when LPM supplemental level was at 300 mg/kg, which were significantly increased by 19.09% and 8.57% compared with the control group (P < 0.05), respectively. Condition factor in LPM supplemental groups was significantly lower than that in the control group, and the viscerosomatic index was significantly decreased by 18.84% in LPM-900 group compared with that of the control group (P < 0.05). The crude protein content in the whole body, protein efficiency rate, and protein deposition rate reached the maximum in LPM-300 group, which were significantly increased by 4.40%, 11.97%, and 7.64% compared with that in the control group (P < 0.05). The activities of protease in the liver and intestine of LPM supplemental groups were significantly increased compared with that of the control group (P < 0.05). When LPM supplemental level was 600 mg/kg, the number, length, and width of intestinal villi of grass carp were significantly higher, and the thickness of the intestinal wall muscle layer was significantly lower than that of the control group (P< 0.05). Dietary LPM had no significant effect on the diversity of intestinal flora of grass carp (P<0.05). When LPM supplemental level was 300 mg/kg, the abundance of Cyanobacteria, Lactobacillus and Clostridium increased significantly (P<0.05). LPM inhibited the proliferation of Aeromonas hydrophila, Vibrio parahaemolyticus, and Nocardia. Dietary LPM had no significant effects on activities of glutamic-pyruvate transaminase and glutamic-oxalacetic transaminase, and the contents of triglyceride and glucose in serum (P>0.05). The contents of serum total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol increased with the increase of LPM supplemental level. The contents of total protein, albumin, and alkaline phosphatase activity in serum in the LPM supplemental group were significantly higher than those in the control group (P<0.05). In conclusion, the diet adding LPM at 300-600 mg/kg improved the growth performance of grass carp via inhibition of the breeding of harmful bacteria, improving intestinal function, and keeping the normal function of the liver.