Studies On Dietary Selenium Requirements Of Juvenile Grass Carp, Ctenopharyngodon Ideelus

Selenium(Se)is one essential trace mineral which plays an important part in growth,immunity and antioxidant activity in animal nutrition.This paper chose juvenile grass carp as experimental object to study the effect of dietary selenium on growth performance,quality,digestive enzyme, antioxidant ability,hematopoiesis function,selenium concentration and histological structure in order to determine dietary selenium requirements for grass carp as well as to discuss the mechanism of selenium on grass carp.The study used Single-factorial concentration grade arrangement.Na₂SeO₃ was added to the basal diet(0.04±0.02 mg Se/kg)constituted with casein,gelatin,dextrin,a-starch,soybean oil,MCC and compound additive at 0,0.15,0.30,0.60,1.20,2.40,4.80 mg Se/kg to put up seven experimental diets which providing 0.04±0.02,0.18±0.02,0.36±0.03,0.66±0.02,1.29±0.07,2.67±0.13,4.05±0.04 mg Se/kg,respectively.The basal diet which is added 0 mg Se/kg was used as control group.540 juvenile grass carp(mean length:10.16±0.14 cm,mean weight:21.20±0.24 g)randomly divided into seven treatments which each had three replicates were put into small-cubage cages(1.0×1.0×1.0 m) to conduct the feeding trial in the ponds with slowly flowing water.At the end of the feeding trial, calculated the growth performance indices;collected samples of serum,muscle,hepatpancreas, intestine to analyze nutritional composition,partial blood index,antioxidant ability and digestive function;observed histological changes of internal organs(hepatopancreas,back muscle and heart) of juvenile grass carp.The main results were summarized as follows:1 Effects of dietary selenium on production performance and feed utilization of juvenile grass carpThe feeding trail results turned out that,the dietary selenium has no significant effect on survival ration(P＞0.05)while remarkably affected specific weight gain(WG),specific growth rates (SGR),feed efficiency ratio(FER),protein efficiency ratio(PER)and protein reservation rates(PRR) of juvenile grass carp(P＜0.05).Diets containing 0.66 mg Se/kg to 2.67 mg Se/kg can remarkable raise the production performances and diets containing 0.66 mg Se/kg to 2.67 mg Se/kg can remarkable raise the feed utilization ration of juvenile grass carp.By regression analysis,when juvenile grass carp has optimal GR,SGR,FER and PER,dietary selenium concentration is 0.631 mg/kg,0.614 mg/kg,0.614 mg/kg,0.614 mg/kg,respectively.2 Effects of dietary selenium on body indices,nutritional composition and partial blood indices of juvenile grass carpThe results turned that dietary selenium has no significant affect on weight/length,visceral index,hepatosomatic index,spleen index and condition factor(P＞0.05);but remarkable affected quality,hemoglobin and red blood cells number of juvenile grass carp(P＜0.05).The crude protein of fish body and muscle as well as hemoglobin and red blood cells number were highest in fish feed diet with 0.66 mg Se/kg;while the fat content is the lowest.3 Effects of dietary selenium on digestive enzyme activities of juvenile grass carpThe results showed that the dietary selenium had a significant effect on digestive enzyme activities of juvenile grass carp(P＜0.05).All the tested groups had higher activities than the control group.Dietary selenium affects the protease and lipase more remarkably.The activities of protease and amylase were higher in intestine while the activities of lipase were higher in hepatopancreas.The activities of the three digestive enzymes were highest with dietary 0.66 mg Se/Kg.4 Effects of dietary selenium on antioxidant function of juvenile grass carpThe results of activities of three antioxidant enzymes such as superoxide dismutase(SOD), catalase(CAT)and glutathione peroxidase(GPX),levels of malondialdehyde(MDA)and total antioxidative competence(T-AOC)in hepatopancreas and serum showed that dietary selenium had significant effects on the antioxidant enzymes activities as well as the MDA and T-AOC(P＜0.05). When 0.60 mg/kg Se added,the activities of GPX,CAT as well as the T-AOC value increased to the highest,while the MDA level decreased to the lowest.All of those mentioned above indicated that a optimum selenium level(0.66 mg Se/kg)could keep the antioxidant enzymes in a balanced level, which could protect grass carp from oxidant damage. 5 Effects of dietary selenium on selenium concentration and deposition of juvenile grass carpThe results showed that dietary selenium had a significant effect on selenium concentration in whole-body,muscle and hepatopancreas as well as selenium deposition and excretion in whole-body of juvenile grass carp(P＜0.05).Selenium concentration in whole-boy and muscle with dietary Se from 0.04 mg Se/kg to 0.36 mg Se/kg as well as selenium concentration in hepatopancreas with dietary Se from 0.04 mg Se/kg to 1.29 mg Se/kg remarkably increased as increasing of dietary selenium,beyond which the selenium concentration had no significant difference(P＞0.05).In the same test group,the highest selenium concentration was found in hepatopancreas while lowest in muscle.The selenium deposition had increased with increasing selenium up to 0.66 mg Se/kg,beyond which it showed a decline tendency.The selenium excretion first increased and then decreased as dietary selenium increased,and the lowest excretion diet of grass carp was loud to be dietary 0.438 mg Se/kg,while the excretion of grass carp feed diets with 0.695 mg/kg was 0 mg.6 Effects of dietary selenium on histological structure of juvenile grass carpThe results of observation to the histological structure of hepatopancreas,back muscle and heart showed that dietary selenium had a significant affect on histological structure of juvenile grass carp.Both low selenium and high selenium were harmful to the histological structure of internal organs of juvenile grass carp.Only optimum dietary selenium(0.66 mg Se/kg)can maintain normal histological structure.All these results demonstrated that selenium was an essential nutrient for grass carp.Dietary selenium requirement for juvenile grass carp was determined as 0.438 mg/kg-0.631 mg/kg by inspecting indices of production performance,feed utilization as well as selenium concentration and deposition of juvenile grass carp.The results also indicated that,dietary selenium can remarkably enhance antioxidant ability,increase digestive faction as well as effectively maintain integrity and functionality of internal organs for juvenile grass carp.