| Egg industry occupies an important position in China’s animal husbandry.In recent years,blue-shell eggs are more and more popular by consumers because of their special color and high nutritional value,blue-shell eggs have been studied a lot.Xinnong blue-shell layers come from the blue-shell egg-laying population of Jianghan chickens and are currently under cultivation.In this study,Xinnong blue egg-shell layers were selected and bred to construct a breeder family to breed the next generation;Through the typing and identification of blue eggshell gene of hens in breeder population,the eggshell color L,a,b values of 30 and 40 weeks old were measured,and the effects of different blue eggshell genotypes(O/O type and O/o type)and week age on eggshell color were analyzed;Through the classification of eggshell color,the differences of different eggshell color grades were compared;Through screening and identification of genetic markers related to blue eggshell color(BLVR,SLCO1B3,HO-1),it is expected to provide some reference for the follow-up study of blue eggshell color,improve eggshell color and speed up the breeding process of varieties.The test results are as follows:1.Through the selection and breeding of Xinnong blue-shell layers,55 blue-shell homozygous cocks and 585 blue-shell layers were established as breeders for the next generation,including 284 O/O type hens and 301 O/o type hens,the ratio of them was close to 1:1.Overall,the laying rate of O/O type hens was about 2% higher than that of O/O type hens,but not significant(P < 0.05);The egg weight of O/o type was 1.1g and 1.7 g higher than that of O/O type at 25 and 40 weeks,respectively.At the same week of age,the egg weight of O/o type was significantly higher than that of O/O type(P < 0.01).The feather color L,a and b values of O/O type were 2.4,1.9 and 3.3higher than those of O/o type,respectively(P < 0.01).2.The eggshell color L,a,b values of 30 and 40 weeks old were measured,and the eggshell color was graded to compare the difference of eggshell color grade and the difference of eggshell color between O/O type and O/o type at different laying stages.The results are as follows:(1)The eggshell color is divided into four grades: dark green(grade Ⅰ),light green(grade Ⅱ),light sauce color(grade Ⅲ)and deep sauce color(grade Ⅳ).Because the dark sauce color is not accepted by the market,only the first three grades of eggshell colors are compared in the experiment.The results showed that with the decrease of eggshell color grade,L value gradually decreased,while a,b value gradually increased.In the values of L,a and b,there were significant differences among different eggshell color grades(P < 0.01).(2)The average eggshell strength of different blue-shell color grades was 39-41 N,the average eggshell thickness of sharp end,middle end and blunt end was 0.31-0.34 mm,and the average egg shape index was 1.28-1.31.The results showed that there was no significant difference between eggshell color grade and eggshell strength,eggshell thickness and egg shape index(P > 0.05),indicating that eggshell color had no effect on eggshell quality in the experimental population.(3)The blue-shell eggs of 30-week-old and 40-week-old breeder chickens were collected to analyze the effect of laying age on eggshell color.The results showed that no matter the overall eggshell color or the eggshell color of O/O type and O/o type,the L value of 40 weeks old was significantly higher than that of 30 weeks old(P < 0.01).The change of L value before and after can be used as an important reference index of lighter eggshell color during laying period.(4)The eggshell colors of O/O type and O/o type were compared and analyzed at the age of 30 and 40 weeks respectively.The results showed that at the same age,there was no significant difference in L value between O/O type and O/o type(P > 0.05),but the a and b values of O/o type were significantly higher than those of O/O type(P < 0.01).The eggshell color of offspring of five parent combinations was analyzed.The results showed that there was a significant difference in eggshell color a between 30 and 40 weeks of age(P < 0.01).And the eggshell color a value of the offspring of the parental combination method O/O♂×O/O♀ is the smallest.Therefore,it is considered that the a value can reflect the depth of the blue-shell color,and a value can be used as a reference index for color classification.3.Through identification,typing and association analysis of candidate gene related SNP in 284 O/O type hens,it was found that there was a significant correlation between SNP(g.5340 G > C)in exon 4 of HO-1 gene and eggshell color b value at 30 weeks old.The eggshell color b value of CC type is significantly lower than that of GC type and GG type.The homozygous mutant CC type in this SNP can be used as a molecular marker to provide assisted selection for the breeding of blue eggshell layers in the later stage. |
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