Differences In Egg Yolk Formation Of Guangxi Ma Chickens With Dissimilar Laying Rates

The formation of yolk in hens is essential for oocyte maturation and ovulation.There is a great difference in laying rates between different age or the same age of Guangxi Ma chickens,whether the difference is related to the different formation of yolk is not clear.This study was conducted to explore the difference of yolk formation in Guangxi Ma chicken with different laying rates from the perspective of synthesis,transference,transportation,and deposition of yolk precursor in liver-blood-ovary axis.According to the age and laying rate,Guangxi Ma hens were divided into five groups:32 weeks（32W）,high（50WH）and low（50WL）laying rates at 50 weeks and high（72WH）and low（72WL）laying rates at 72 weeks.The main findings were as follows:（1）Difference in yolk precursor formation of Guangxi Ma Chickens with dissimilar laying ratesYolk precursor is synthesized in liver and transported to ovary by blood circulation.We detected the content of yolk precursor in liver-blood-ovary axis of hens in each group to explore the difference of yolk precursor formation in hens with dissimilar laying rates.The results showed that the content of yolk precursor in liver,serum and ovary decreased significantly during aging process;TG,HDL-C and VLDL-C contents in serum and ovaries,as well as HDL-C and VLDL-C levels in liver tissues of 50WL and 72WL were significantly lower compared to hens in 50WH and 72WH,respectively.However,no significant difference was detected in liver TG and T-CHO levels in 50WL and 50WH.The above results indicate that age-related decrease of laying rates in hens is related to decrease of yolk precursor synthesis and transportation ability,and the difference of laying rates in hens of the same age may be related to the difference of transference capacity of liver yolk precursor.（2）Difference of antioxidant capacity in livers,serum,and ovaries of Guangxi Ma Chickens with dissimilar laying ratesNormal physiological state of liver-blood-ovary axis is essential for yolk formation.We first compared the differences of liver index,morphology,cell proliferation and apoptosis in each group,and then detected the antioxidant capacity of livers,serum,and ovaries in each group.The results showed that the capacity of hepatic cell proliferation and anti-apoptosis as well as the antioxidant capacity of the livers,serum and ovaries decreased significantly during aging process.The results indicate that age-related decrease of laying rates in hens is related to the decrease of the capacity of hepatic cell proliferation and anti-apoptosis as well as the antioxidant capacity of livers,serum,and ovaries.The proliferation and anti-apoptosis of hepatic cells and the antioxidant capacity of livers and ovaries were remarkably lower in hens in50WL and 72WL than those in 50WH and 72WH,respectively.The results indicate that the difference of laying rates in hens of the same age is related to difference of hepatic cell proliferation and anti-apoptotic capacity as well as antioxidant capacity in livers and ovaries.（3）Difference in the synthesis and transference capacity of yolk precursor in liver of Guangxi Ma chickens with dissimilar laying ratesThe synthesis of yolk precursor in hen liver is regulated by E₂.We detected serum E₂ level,the expression of genes and proteins related to lipid metabolism in each group of hens.The results showed that serum E₂ level and the expression of genes and proteins related to lipid metabolism decreased significantly during aging process.The results indicate that age-related decrease of laying rates in hens is related to the decrease of liver yolk precursor synthesis and transference ability.The expression levels of ERαand genes related to lipid transference in liver tissues were remarkably lower in hens in 50WL and 72WL than those in 50WH and 72WH,respectively.Combined with the result of oil red O staining,it is further indicated that lipid transference is impaired in livers of hens with low laying rates at the same age.In summary,the age-related decline of laying rates in Guangxi Ma chickens is related to the synthesis,transference and transportation of yolk precursor and the antioxidant capacity of livers,serum,and ovaries.And the non-age related decline of laying rates in Guangxi Ma chicken is related to the transference of yolk precursor and the antioxidant capacity of livers and ovaries.