Studies On Application Of Lysozyme In The Feed Of Allogynogenetic Silver Crucian Carp (ASCC) And Grass Carp (Ctenopharyngodon Idellus)

The further development of aquaculture was limited by problems such asantibiotic residue, resistance to antibiotics, as the intensive culture developed.Development of new safety feed additives was very important to solve the problems,in which lysozyme product was the better one.This research was conducted to study the application possibility and the suitabledosage of lysozyme in the allogynogenetic silver crucian carp and grass carp diets bythree tests. The first test was a study of application of lysozyme to the feedstuff ofallogynogenetic silver crucian carp. The lysozyme product was optimized throughfilm-dispersion method in settlement of problems which appeared in Part1. Part2andPart3studied the stability and the application of the coated lysozyme production ingrass carp feed.Part1: The allogynogenetic silver crucian carp used in the test were kept incement tank with control feedto suit for the environment for40d. Using single factorexperimental designs, the test allogynogenetic silver crucian carp(initial body weight28.11±2.14g) were randomly divided into11groups with4replications and eachtreatment had30allogynogenetic silver crucian carp individuals, culturing in cagewith2m×0.75m×1.0m.11experimental diets were formulated containing0(control),10mg/kg (L1),20mg/kg (L2),30mg/kg (L3),40mg/kg (L4),50mg/kg(L5)lysozyme and2g/kg(EL1),4g/kg(EL2),6g/kg(EL3),8g/kg(EL4),10g/kg(EL5)encapsulated lysozyme (EL) with the same lysozyme activity as the L groupsrespectively, to feed allogynogenetic silver crucian carp for60d. The mainly aim wasto study the influence on growth performance and anti-infection ability by thelysozyme and the encapsulated lysozyme. The result showed that the RGR of EL1andEL3were higher than control and the RGR of L5was lower than control, and nodifference between control and other groups. The FCR of EL1, EL2and EL3werelower than the control (P<0.05), and EL5was higher than the control, while the FCR of L5was higher than the control, and no difference between L1, L2, L3, L4and thecontrol. Aafter Aeromonas hydrophila infection, the death rate of both lysozymegroups and encapsulated lysozyme groups were lower than the control group. Thechange of endogenous enzymes activity affected by Lysozyme and encapsulatedlysozyme was uniform. Considering lysozyme and encapsulated lysozyme played therole of enhacing anti-infection ability more obviously than growth performance,moreover the encapsulated lysozyme was more effective, and the optimal additionlevel of encapsulated lysozyme was2g/kg-6g/kg in the test condition.Although we found that the encapsulated lysozyme had some shortages, such asnonstability of lysozyme and its particle size affecting mixture uniformity in the feed,so we prepared another encapsulated lysozyme product by in film-dispersion method.Part2: Four experiments were designed: characteristic test, environmentsimulation test, in-vitro digestion test and storage test. That Comparing lysozymeactivity in different temperature and pH showed the characteristic of the lysozymeproduct. The result showed that the lysozyme product had the best activity at about80℃and with pH changing from3.0to8.0the lysozyme activity had no significant change.Environment simulation test was mainly to study the activity change of lysozyme byextrude and high temperature treatments. The result showed that the lysozyme activityhad no marked change.The lysozyme activity changed in different degree treated bydigestive enzymes from different parts of digestive tract of grass carp,allogynogenetic silver crucian carp and common carp. And the change was marked inmidgut and in grass carp digestive tract. The lysozyme activities in the feed decreasedsignificantly in30-days and keep good stability until120d in200-400mg/kg groups.The lysozyme activities continued to decline with conservation time extending in500mg/kg group, and showed a broken line decline in100mg/kg group.Part3: An experiment was conducted to evaluate the use of the role of theencapsulated lysozyme product by in film-dispersion method for grass carp. Grasscarp with initial body weight (6.93±0.01)g were randomly divided into five groupsand fed the corresponding feeds with0mg/kg (control),100mg/kg,200mg/kg,300mg/kg,400mg/kg and500mg/kg dietary lysozyme respectively for60days, eachtreatment represented by5replicates of70fish and parameters of growth performanceand anti-infection ability were calculated and determined. The results indicated thatdifferent dosages of dietary lysozyme affected the growth performance of grass carpin varying degrees. At the forty-fifth day of the feeding trial, the special growth in all lysozyme groups were significantly lower than that of the control group (P<0.05).There were no significant differences on SGR between100-300mg/kg groups and thecontrol group at the last phase. But the SGR in the last two groups was lower than thatin the control (P<0.05). Feed coefficient presented the trend of first decrease thenincrease with the increase of the dietary lysozyme concentration, which in the groupof200mg/kg was the lowest. After challenged with live Aeromonas hydrophila byintraperitoneal injection, mortality of the test groups (200mg/kg-500mg/kg) weresignificantly lower than that in the control group and100mg/kg group. This studyfurther showed that activities of endogenous digestive and immune enzymes affectedto some extent by the lysozyme product. Besides, we also found that it possessedstrong inhibitory activity against common Gram negative bacteria such as Aeromoneshydrophila, Vibrio harveyi, Vibrio Alginolyticus, Vibrio Parahaemolyticus in aquacultureby antimicrobial tests. In summation, it was proved that the optimal addition level oflysozyme product was200mg/kg-300mg/kg according to growth parameters and theanti-infection ability.