Age-related changes of yolk precursor formation in the liver of laying hens

Abstract

A rapid decline in egg production of laying hens begins after 480 d of age. Such a rapid decrease results predominantly from the ovarian aging, accompanied by endocrine changes, decreased yolk synthesis and accumulation, and the reduction in follicles selected into the preovulatory hierarchy. In this study, hens at 90, 150, 280, and 580 d old (D90, D150, D280, and D580, respectively) were compared for yolk precursor formation in the liver to elucidate effects of aging on laying performance. The results showed that liver lipid synthesis increased remarkably in hens from D90 to D150, but decreased sharply at D580 as indicated by the changes in triglyceride (TG) levels. This result was consistent with the age-related changes of the laying performance. The levels of liver antioxidants and total antioxidant capacity decreased significantly in D580 hens and the methane dicarboxylic aldehyde in D580 hens was much higher than that at other stages. The serum 17β-estradiol level increased from D90 to D280, but decreased at D580 (P<0.05). The expression of estrogen receptor α and β mRNAs in the liver displayed similar changes to the serum 17β-estradiol in D580 hens. Expressions of the genes related to yolk precursor formation and enzymes responsible for fat acid synthesis were all decreased in D580 hens. These results indicated that decreased yolk precursor formation in the liver of the aged hens resulted from concomitant decreases of serum 17β-estradiol level, transcription levels of estrogen receptors and critical genes involved in yolk precursor synthesis, and liver antioxidant status.

Keywords: Lipid metabolism; Yolk precursor formation; 17β-Estradiol; Antioxidant; Hen.

Fig. 1

Changes of TG and T-CHO levels in the liver, serum, and ovary in hens of different ages TG (a, c, e) and T-CHO (b, d, f) levels were determined in the liver (a, b), serum (c, d), and ovary (e, f) of hens aged 90, 150, 280, and 580 d. Data were expressed as the mean±SE (n=10). Different uppercase and lowercase letters indicate a very significant difference (P<0.01) and significant difference (P<0.05), respectively. prot: protein

Fig. 2

Liver antioxidant levels in hens of different ages Levels of GSH (a), T-SOD (b), T-AOC (c), GSH-Px (d), CAT (e), and GSH-ST (f) were determined in hens aged 90, 150, 280, and 580 d. Data were expressed as the mean±SE (n=10). Different uppercase and lowercase letters indicate a very significant difference (P<0.01) and significant difference (P<0.05), respectively. prot: protein

Fig. 3

Liver MDA and H₂O₂ levels in hens of different ages Levels of MDA (a) and H₂O₂ (b) were determined in hens aged 90, 150, 280, and 580 d. Data were expressed as the mean±SE (n=10). Different uppercase and lowercase letters indicate a very significant difference (P<0.01) and significant difference (P<0.05), respectively

Fig. 4

Levels of serum E₂ in hens of different ages Data were expressed as mean±SE (n=10). Different uppercase and lowercase letters indicate a very significant difference (P<0.01) and significant difference (P<0.05), respectively

Fig. 5

Expression of ER-α (a), ER-β (b), and GPR30 (c) mRNAs in liver of hens of different ages Data were expressed as mean±SE (n=10). The relative abundance of each transcript was normalized to β-actin and expressed as fold changes over D90 pullets. Different uppercase and lowercase letters indicate a very significant difference (P<0.01) and significant difference (P<0.05), respectively

Fig. 6

Transcription levels of genes related to yolk precursor synthesis in hens of different ages Transcription levels of VTGII (a), ApoVLDLII (b), ApoB (c), SREBP (d), FAS (e), ACC (f), MTP (g), ACLY (h), SCD (i), MALI (j), PPARα (k), and PPARγ (l) in livers of hens aged 90, 150, 280, and 580 d. Data were expressed as the mean±SE (n=10). The relative abundance of each transcript was normalized to β-actin and expressed as fold changes over D90 pullets. Different capital and lowercase letters indicate a very significant difference (P<0.01) and significant difference (P<0.05), respectively