Effects Of Dietary Vitamin D₃ On Growth And Innate Immune Response Of Yellow Catfish,fed With Low-phosphorus Diets

Yellow catfish?Pelteobagrus fulvidraco?is an important aquaculture species in China,and its production has been increasing in recent years.Vitamin D₃ is a kind of fat-soluble vitamin,in addition to regulate calcium and phosphorus metabolism,it can also affect the body's immune function.This study explored the effects of vitamin D₃ added to low-phosphorus feed on the growth,fish body composition,serum biochemical indicators,antioxidant capability,proliferation activity and apoptosis of macrophage and toll-like receptors of juvenile yellow catfish,aiming to provide a theoretical basis for the production of high-efficiency low-phosphorus feed.In growth trial,the yellow catfish with an initial body weight of 5.0±0.2g,were fed with 5 kinds of feeds containing graded levels of vitamin D₃i.e.1120,2260,3950,8030 and 16600 IU/kg,casein,skim milk powder and corn protein powder as protein sources,soybean oil as fat source and phosphorus content of 0.34%for12weeks,then detected the weight gain rate and fish composition.After the growth trial,Edwardsella ictaluri was intraperitoneally injected for 90 hours to test the innate immune indicators.The results are as follows:1. Dietary vitamin D₃ had no effect on the survival rate of P.fulvidraco?P>0.05?.The weight gain rate and feed efficiency of the P.fulvidraco reached the peak with the vitamin D₃ concentration of 16600 IU/kg.There was no significant difference in water content,crude protein,crude fat and ash content between the 5 groups?P>0.05?.After Edwardsiella ictaluri challenge,the cumulative mortality of P.fulvidraco decreased and the immune protection rate increased with the increase of vitamin D₃concentration in the feed.2. The concentration of glucose,cholesterol,albumin and transaminase in serum of P.fulvidraco were significantly affected by dietary vitamin D₃ levels?P<0.05?,After challenge,the concentration of total protein,triglyceride and transaminase in serum of P.fulvidraco were significantly increased?P<0.05?;Before the challenge,the concentration of catalase?CAT?and total superoxide dismutase?T-SOD?in serum of P.fulvidraco were significantly increased with the vitamin D₃ concentration of2260 IU/kg,After challenge,the T-SOD in serum of P.fulvidraco was significantly decreased with the vitamin D₃concentration of 2260 IU/kg?P<0.05?,the lysozyme?LYZ?in serum of P.fulvidraco was significantly increased with the vitamin D₃concentration of 8030 IU/kg?P<0.05?.Dietary vitamin D₃ did not influence the serum T-SOD,malonaldehyde?MDA?,LYZ,and glutathione peroxidase?GSH-Px?of P.fulvidraco?P>0.05?,While after challenge,the liver CAT,LYZ and GSH-Px were significantly decreased with the increase of dietary vitamin D₃ concentration?P<0.05?.3. After Edwardsiella ictaluri challenge,the proliferation activity of macrophage in head kindey of P.fulvidraco responded to dietary vitamin D₃ levels?P<0.05?,the apoptosis rate was the lowest with the vitamin D₃ concentration of 16600 IU/kg?P<0.05?,The effect of vitamin D₃ on proliferation and apoptosis of macrophages reduced with the increase of challenge time.The reactive oxygen?ROX?of macrophages was the highest for 1120 IU/kg level?P<0.05?,but with the increase of challenge time,the 16600 IU/kg diet was significantly increased?P<0.05?.After challenge,phagocytic activity of macrophages was significantly increased in the16600 IU/kg level?P<0.05?.4. Edwardsiella ictaluri challenge significantly increased the expression of TLR18,TLR19 and TLR21 genes,after the challenge,TLR18 m RNA expression level in the head kidney was the lowest at 8030 IU/kg diet?P<0.05?,In the spleen,the TLR18 m RNA expression level decreased with the increase of vitamin D₃in diet,TLR18 m RNA expression level in the liver was the highest at 16600 IU/kg diet?P<0.05?,while it was the lowest at 3950 IU/kg diet?P<0.05?,The expression of TLR18 m RNA in the anterior intestine was significantly higher in the low-concentration?1120 IU/kg?vitamin D₃ diet.TLR18 m RNA expression level in the head kindey was the highest at 16600 IU/kg diet,but there was no significant difference?P>0.05?.The expression of TLR19 m RNA in spleen,liver and anterior intestine decreased significantly with the increase of vitamin D₃.After the challenge,TLR18 m RNA expression level in tissues decreased significantly with the increase of vitamin D_3,Among the four immune tissues,the 3 genes expression in the high-concentration VD₃ diet?16600 IU/kg?was significantly lower than other diets.Therefore,this experiment showed that within VD₃ concentration range of this experiment,dietary vitamin D₃ had no effect on the growth of P.fulvidraco,but the feed efficiency had been improved in high VD₃ diet.Dietary VD₃ had raised the immune protection rate,oxidation resistance,and lysozyme activity,promoted phagocytosis of macrophages,reduced apoptosis and ROS production,inhibited the expression of TLR18,TLR19 and TLR21 in the spleen,which has the highest expression among immune tissues,so the dietary VD₃ can improve innate immune response of P.fulvidraco,and this is dose-effect relationship.However,high dietary concentrations may damage liver tissue cells,leading to the level of alanine aminotransferase?ALT?and aspartate transaminase?AST?in serum of P.fulvidraco.