| In poultry production,the phenotypes of dermal hypermelanization and green shank are two traits economically important.Dermal hypermelanization of black chicken affects the market acceptance of the product,and for yellow broiler,shank green will have a very negative impact on the sales of the product.The dermal hypermelanization trait was caused by duplication of two DNA fragments(Dup1 and Dup2)at FM locus on chromosome 20,while the green shank phenotype was regulated by Id locus on chromosome Z.Lueyang chickens,Jinling black chickens and Jinling yellow broilers were used to analyze the association between FM and Id locus genotypes and the phenotypes of dermal hypermelanization and green shank,and to explore the feasibility of using these locus in molecular-assisted breeding of these traits,to analyze the variation of dermal hypermelanization trait with chicken age and weight,and to study the effects of age,feed and drugs on ratios of green shank.These traits were regulated from the feeding and management,and the varieties that met the market demand were cultivated.Exp.1: Variation regularity of dermal hypermelanization and establishment of related molecular breeding methodsA total of 704 5-week-old Lueyang chickens were randomly selected,at 6,10,14 and 18 weeks of age,skin color was measured by portable chromatometer,body weight and gender were recorded.Darkness was quantified by L value of L*a*b system,the smaller the L value,the darker the skin.The results showed that L value of skin color of lueyang chicken gradually increased with age(6wk: 39.02±3.35 < 10wk: 44.08±3.51 < 14 wk: 45.97±4.23 < 18 wk: 46.75±3.79;P<0.05),and there was no interaction between the variation regularity of dermal hypermelanization and sex.The heritability of dermal hypermelanization decreases with age(6wk: 0.68 > 10wk: 0.54 > 14 wk: 0.49 > 18 wk: 0.42).There was a strong positive correlation between skin color L value and body weight(r = 0.592-0.660,P<0.01).Three chicken breeds with different skin color traits and known genotypes included Jinling Black Phoenix Chicken(W line),Jinling TieMa Chicken(A line)and Fengming Black Chicken(WT line),among them,the W line were homozygote of dermal hypermelanization(FM/FM),the WT line were heterozygote(FM/fm),and the A line were recessive homozygote(fm/fm).The copy number distributions of Dup1 in the above three lines were detected by QPCR.The results showed that the relative copy number of Dup1 of W line(FM/FM),WT line(FM/fm)and A line(fm/fm)was 1.85±0.52,1.37±0.43,1.04±0.32,respectively,which is basically consistent with the theoretical copies of three lines.If the threshold for elimination of heterozygotes is 1.6,the accuracy is 74%.Exp.2: Genetic analysis of green shank trait and the effect of age,feed and drug on its ratios in yellow broilersA total of 1950 day-old chicks were used which were randomly grouped into three groups of complete formula feed(CCF),self-formulating feed(SFF)and florfenicol-supplemented SFF(Flor-SFF).Ratios of green shank in the three groups were respectively recorded in 21 and 45 days and the effects of age,feed and drug on the ratio of green shank were analyzed.30 yellow-shank broilers and 26 green-shank broilers were selected from the yellow broiler populations to elucidate the correlation between the sequence variation of BCDO2 gene and Id locus and green shank.Ratios of green shank significantly(P<0.05)decreased in the CCF and SFF groups as chicks grew.But,the ratio similarly decreased in the Flor-SFF group(P>0.05).In 21 days,the ratio(49.8%)in the Flor-SFF group was significantly(P<0.05)lower than ones in the CCF(55.8%)and SFF(61.1%)groups.But,the CCF group showed the lowest ratio(28.5%)of green shank in 45 days.This study proved that the correlation between Id locus and green shank phenotype of Jinling yellow broilers was not significant(P>0.05),but yellow broilers carried BCDO2 gene,which laid a genetic foundation for non-genetic factors such as feed and drug to regulate the ratio of green shank phenotype.Generally,dermal hypermelanization and green shank belong to quality traits regulated by a few genes.This study first found that non-genetic factors such as age,weight and feed significantly affecting the penetrance of these traits.The darkness of dermal hypermelanization faded with age,which reclaims a new research field to explore the interaction between the genetic basis of dermal hypermelanization and environment in the future,meanwhile,it is suggested that meat-type black chicken of Slaughter time should not be too late.Traditional phenotypic selection could not identify heterozygotes as an important reason for the selection of black chickens,in this study,the accuracy of identifying heterozygotes with Dup1 copy number 1.6 as the threshold was 74%.Genetic basis of the phenotype of green shank was not clear,therefore,adding natural pigments such as xanthophyll and riboflavin to the feed is an effective measure to solve the problem of green shank of yellow broilers. |
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