Analysis Of Thick And Thin Albumen Content In Chicken Egg And Candidate Genes Identification

The albumen is the important part of chicken egg. The albumen involves the thick albumen and the thin albumen. The content and ratio of thick and thin albumen closely associate with the thickness and the visual effect of albumen. In the present study, the contents of thick and thin albumen were analyzed in different chicken breeds and at different ages, and the candidate genes associated with the content and ratio of thick and thin albumen were identified. The results are helpful in breeding for layer of high egg quality.The percentages of yolk, thick albumen, thin albumen and the ratio of thick to thin albumen in eggs from Hy-line Brown, Huainan chicken, Hoddan, and line D1 at 40 wks of age were analyzed. The results showed that, compared to Hy-line Brown, the percentages of thick albumen from eggs of Huainan chicken, Hoddan, and line Dl were lower (P<0.05), while the percentages of yolk were higher (P<0.05). The ratio of thick to thin albumen of Hy-line brown hens is the highest (1.19), while that of Hoddan is the lowest (0.91).In line D1, the percentages of yolk, thick albumen, thin albumen and the ratio of thick to thin albumen in eggs from hens at 30,40, and 50 wks of age were analyzed, respectively. The results showed that the ratio of thick to thin albumen increased with the age, and the percentages of thick albumen, thin albumen and yolk in 30 wks of age significantly correlated (P<0.05 or P<0.01) to those in 40 and 50 wks of age, respectively, the percentage of thin albumen as well as the ratio of thick to thin albumen were positively correlated to egg weight (P<0.01 or P<0.05), and the percentage of yolk was negatively correlated to egg weight (P<0.01). However, the percentages of yolk, thick albumen, thin albumen and the ratio of thick to thin albumen were not significantly correlated to Haugh unit (P>0.05).The ratio of thick to thin albumen was tested in a Hoddan population (N=300) at 300 d of age. According to the data, two tails,15 hens for each, were used as experimental animals, high ratio group (HG) and low ratio group (LG). Tissues of protein secretion of oviduct were collected in HG and LG in 2 hours after laying. Three samples of HG and LG, respectively, were randomly selected for digital gene expression (DGE) analysis. There were 95 differentially expressed genes identified by DGE analysis, including 8 molecular functional genes. The differentially expressed gene Smadl and non-differentially expressed gene ERN1 were selected and qPCR was performed for verification. Results showed that the level of Smadl mRNA in LG was higher than in HG (P<0.05), and the level of Smadl mRNA was negatively correlated to the percentages thick albumen and the ratio of thick to thin albumen (P<0.05), and was positively correlated to the percentages thin albumen (P<0.05). The level of ERN1 mRNA in LG and HG did not differ (P>0.05). Therefore, Smadl could be regarded as a candidate gene for the content of thick and thin Albumen in chicken egg.