纳米缓释丁酸钠对草鱼生长性能、血清生化指标、肠道黏膜形态及PepT1基因表达的影响

以初始体重(18.65±0.21) g的草鱼为实验对象,研究不同浓度纳米缓释丁酸钠对草鱼的生长性能、血清生化指标、肠道黏膜形态及PepT1基因表达的影响,实验共配制6种等氮等能的草鱼实验饲料,在基础饲料中分别添加0、0.1%、0.2%、0.4%、0.6%和0.8%的纳米缓释丁酸钠,以不添加丁酸钠组为对照组。实验在室外网箱内进行,每网箱饲养50尾草鱼,每个处理重复3次,养殖时间60d。结果表明:当纳米缓释丁酸钠添加量为0.6%时,草鱼的增重率、特定生长率、肥满度和肠绒毛高度均显著高于对照组(P<0.05),具有较好的促进生长的作用;同时,草鱼血清中的球蛋白含量显著增加(P<0.05),尿素氮含量与对照相比显著降低(P<0.05),谷丙转氨酶GOT、谷草转氨酶GPT及葡萄糖含量与对照相比差异不显著;血清中总氨基酸含量及必需氨基酸含量相比对照组增加显著(P<0.05),小肠中PepT1基因表达量提高显著(P<0.05)。在饲料中添加适量的纳米缓释丁酸钠通过保护肠道黏膜和提高肠道PepT1的表达量,从而促进其生长,适宜添加量为0.6%。

EFFECTS OF SUSTAINED RELEASE NANOSPHERE SODIUM BUTYRATE ON THE GROWTH PERFORMANCE,SERUM BIOCHEMICAL INDICES,INTESTINAL MUCOSAL MORPHOLOGY AND PEPT1 mRNA EXPRESSION IN INTESTINAL OF GRASS CARP (CTENOPHARYNGODON IDELLUS)

Sodium butyrate is an important feed additive, which can be quickly absorbed by the intestinal tract. It can promote the proliferation and maturation of intestinal cells, maintain the integrity of intestinal mucosa and improve the digestion and absorption of nutrients in the small intestine. It was found in piglets and chicks that sodium butyrate could decrease the feed coefficient and increase the weight gain rate. Meanwhile, it also can regulate the ecological balance of microorganisms in the intestinal tract of animals and improve the immune function of the organism. The application of sodium butyrate in aquatic animal feed has also been reported. Some previous studies suggested that sodium butyrate significantly promoted the growth performance of sturgeon and Litopenaeus vannamei, but there were few literatures on the effects of sodium butyrate on the absorption and transport of protein and small peptides in intestine of aquatic animals. The active ingredient of sodium butyrate is butyric acid, which has volatile and unpleasant sour smell. In the application of butyric acid, in order to overcome these shortcomings and achieve the effect of promoting production on aquatic animals, sodium butyrate is generally treated by envelopment technology, so as to achieve the purpose of fixed point and delayed release. To explore effects of dietary nano slow-release sodium butyrate on grass carp (Ctenopharyngodon idellus) growth performance, serum biochemical indices, intestinal mucosal morphology and intestinal PepT1 mRNA expression, we conducted a 60-day feeding trial with different levels of nano slow-release sodium butyrate in the diet. Six isonitrogenous and isoenergetic diets were formulated with 0, 0.1%, 0.2%, 0.4%, 0.6% and 0.8% nano slow-release sodium butyrate in the basal diet. The feeding trial was carried out in an outdoor cage farming system (cage size: 200 cm×200 cm×250 cm). Each diet was randomly assigned to three net cages with 50 fish [initial body weight of (18.65±0.21) g] per cage for three times (8: 30, 12: 30 and 16: 30) per day. The feeding quantity in the first week was 5% of the fish body quality, and then increased by 1% every week. Daily record of weather conditions, water temperature, feeding quantity and feeding status. At the terminal of the feeding trial, fish from each cage were weighed the total weight and recorded the total number after fasted 24h. Six fish per cage were collected to measure the body length and body weight for the calculation of condition factor (CF). The blood sample was drawn from the caudal vein of six another fish per tank with a disposable syringe and kept at 4℃ for 24h, then centrifuged at 3000×g for 15min to get serum and stored at –80℃ for analysis of serum total protein, glutamic oxalacetic transaminase (GOT) and glutamate pyruvate transaminase (GPT), urea nitrogen and other indices. Also, six fish were randomly selected from each repeat, the foregut was separated and stained with HE method, then observed under an ordinary optical microscope (40×), villi height and crypt depth were measured and the ratio of villi height to crypt depth was calculated. Intestinal PepT1 gene expression level was analyzed according to Kenneth et al., and the relative expression level of the target gene in the intestinal tract was determined by real-time polymerase chain reaction (PCR) method. The crude protein, crude fat, moisture and ash content in experimental diets were determined by AOAC (2003) standard method. The results showed that weight gain rate, specific growth rate, CF and intestinal villi height of grass carp in 0.6% sodium butyrate group were significantly higher than those of the control group (P<0.05). 0.6% sodium butyrate supplement significantly increased serum globulin, serum total amino acids and serum essential amino acids and significantly decreased serum urea nitrogen (P<0.05). 0.6% sodium butyrate supplement significantly increased the expression of PepT1 in intestine (P<0.05) without impacting Glutamic oxalacetic transaminase (GOT), Glutamate pyruvate transaminase (GPT) and the content of glucose (P>0.05). In conclusion, the supplementation of 0.6% nano sustained-release sodium butyrate into juvenile grass carp diet can protect intestinal mucosa, induce PepT1 expression and promote its growth performance. The results of this study will fill in the blank of the research on the effect of sodium butyrate on the absorption and transport of intestinal protein and small peptides in aquatic animals. Moreover, the present research systematically analyzed the positive effects of nano-slow-release sodium butyrate on the growth performance and intestinal health of grass carp, which will provide an important theoretical basis for the promotion and application of sodium butyrate in grass carp diet.