| China is a big producer of fowl and eggs.The egg incubation is an important link in poultry production.Poultry eggs are commonly incubated in completely dark,but the green light has been proved to be able to affect the embryonic development and hatching process.Our works include investigating the dose-effect relationships between green light and chick embryonic development and metabolism during incubation,investigating changes of eggshell characteristics during incubation and nutrients at hatching periods based on optimized green light dose,analyzing the physiological mechanisms of green light inducing hatching and reducing embryo death from the views of energy supply and eggshell characteristics and providing practical theory guidance for industrialization of lighted incubation.Meanwhile we explore ways to optimize hatch window of hatching eggs,and further improve hatching efficiency without affecting the quality of hatched chickens.The main research contents and conclusions are listed as follows:(1)The effects of LED green light dose on embryonic development and metabolism during incubation900 eggs from 'Linnanhuang' broiler hens were incubated under different intensities(30-80 lux and 120-200 lux)of LED green light to study the effects on embryonic development and metabolism during incubation,and the best light intensity model(120-200 lux)was selected for next step.Based on the best light intensity model,we controlled the light duration(0L:24D,6L:18D,12L:12D and 18L:6D)to provide different doses of green light.We aimed to investigate the dose-effect relationships between green light and chick embryonic development and metabolism during incubation from views of embryo growth,organ development,nutrient transformation and respiration rate.The results showed that the green light improved the body weight of hatched chicks(P<0.05)and the absorption of yolk sac(P<0.05),and the green light dose showed linear correlation with body weight and absorption of yolk(R2=0.9953,P<0.01;R2=0.9968,P<0.01);Green light significantly induced the absorption of lipid in yolk(P<0.01)and accumulation of hepatic glycogen(P<0.01),and the green light dose showed linear positive correlation with lipid absorption and glycogen accumulation(R2=0.9726,P<0.05;R2=0.7842,P>0.05);Green light significantly increased the respiration rate of embryos(P<0.05)even though the green light was removed and the green light dose showed linear positive correlation with the respiration rate of embryos.Therefore,the LED green light has dose-effect relationships with embryonic development and metabolism.(2)The effects of LED green light on eggshell characteristics during incubationAs the phenomenon of eggshell color change found during incubation,we divide 400 eggs into groups according to the eggshell color.We aimed to explore the changes of chromaticity,pigments,elements and apparent structure of eggshell during green lighted incubation.The results showed the green light significantly change the chromaticity mainly caused by significant increase of a*value(P<0.0001);The pigments decreased during incubation but the biliverdin content of green light group were higher than that of dark group(19.2%,P<0.01);Main element contents in eggshell changed,of which phosphorus content increased gradually(P<0.001)and both potassium and sodium contents decreased significantly(P<0.001),meanwhile the green light promote the decline in calcium content(1%);Both pore area and morphology of eggshell were altered after incubation and LED green light enhanced these change.All results above could provide practical theory guidance for lighted incubation.(3)The effects of LED green light on embryo tissue and nutrient for hatching energy supply during incubationWe explored the changes of yolk and liver tissue and nutrients inside of 900 'Linnanhuang' broiler eggs at several key time nodes in hatching stage,and compared the miRNA expression in embryo liver tissue of both green light and dark groups.The results showed that the green light significantly promoted the absorption of yolk sac(P<0.05)and utilization of lipid in yolk(P<0.05),and improved glycogen reserve in liver compared to dark incubation;The difference in expression of miRNA in liver tissue illustrated that green light enhanced the hepatocyte proliferation ability(P<0.05)and induced lipid metabolism in the liver of the embryonic stage(P<0.05).Therefore,we assumed that the LED green light promoted tissue development and nutrient reserve of embryos for hatching energy supply so that the hatching process was accelerated.(4)Mechanism of embryo death during hatching stage and positive effect of LED green light on embryo hatching We focused on the dead embryos which normally developed but unable to hatch.The structural features of the outer surface and the section of the eggshell as well as tissue and nutrients related to hatching energy supply were compared between dead embryos and live embryos.The results demonstrated that dead embryos had bigger yolk sac and liver(P<0.05),and were lower in absorption of lipid in yolk and glycogen reserve in liver(P<0.05);Dead embryos had thicker eggshell(P<0.05)and smaller pore area because of covered by colloid.Thus,we assumed that the LED green light stimulation enhanced nutrient metabolism and maintained the dynamic equilibrium of energy supply during hatching stage,meanwhile decrease in thickness of eggshell reduced the difficulty for embryos breaking the eggshell so that embryos were easier to hatch.(5)Effects of mixing eggs of different initial incubation time on the hatching pattern,chick embryonic development and post-hatch performanceThe eggs started incubation 12 h apart to obtain developmental distinction,and then the eggs of different initial incubation time were mixed on day 12 of incubation.The embryonic development,hatching pattern and post-hatch performance of all groups were investigated.The results demonstrated that mixing eggs of different initial incubation time delayed the hatching process 6 h,while hatch window were narrowed from 30 h to 21 h and peak hatching period were shorten to 5.4 h;The manipulation of mixing eggs did not alter the embryonic development and yolk absorption as well as organ development;The body weight and metatarsal bone length post hatch were also not affected by egg redistribution.As a whole,it was found that mixing eggs of different initial incubation time did not affect embryonic development and post-hatch performance but shortened the hatch window by delay the onset of hatching process. |
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