The underlying mechanism behind the deteriorated laying performance of aged laying hens remains unclear. In the present study, the laying performance and gene expression along the hypothalamus-pituitary-gonad axis were determined. A total of 300 healthy 90-wk-old ISA hens with similar body weights were classified into three groups according to their laying rate between 90 and 94 wk of age. The experimental groups were the low laying rate (<60%, LLR), high laying rate (>85%, HLR), and intermediate laying rate (60% < laying rate < 85%, MLR) hens. At the end of 94 wk of age, eight hens were randomly selected from each group for tissue collection. The gene expression of hormones and their receptors were determined in the hypothalamus, pituitary, and follicles. The results showed that the serum 17-β-estradiol had no significant difference among the three groups. However, the level of insulin-like growth factor 1 (IGF1) in LLR hens was significantly decreased in the serum, small white follicles (SWF), and dominant follicles (DF, P < 0.05). Within the hypothalamus and small yellow follicles (SYF), the mRNA expression level of estrogen receptor was higher in the MLR group (P < 0.05). Compared with HLR hens, the steroid hormone-synthesis key gene, CYP19A1 was significantly decreased in the SWF of MLR-hens and DF of MLR- and LLR-hens (P < 0.05). The mRNA expression level of IGF1 receptor was higher in the hypothalamus, pituitary, SWF, large white follicles (LWF), SYF, and DF of LLR hens, compared to the HLR hens (P < 0.05). These results suggest that decreased IGF1 in serum and follicles was associated with the decreased egg production of aged laying hens. The present study provides novel insights into the endocrine changes in aged hens having different egg production.
Keywords: hormone; hypothalamus–pituitary–gonadal axis; insulin-like growth factor-1; laying hen; laying rate.
The level of insulin-like growth factor 1 (IGF1) in low laying rate hens was significantly decreased in the serum, small white follicles, and dominant follicles. In the hypothalamus and small yellow follicles, the mRNA expression level of estrogen receptor in low laying rate hens was higher than in the medium laying rate hens. Compared with the high laying rate hens, the steroid hormone-synthesis gene, CYP19A1 was significantly decreased in the small white and dominant follicles of medium laying rate hens, as well as in the dominant follicles of low laying rate hens. Additionally, the mRNA expression level of IGF1 receptor was increased in the hypothalamus, pituitary, small white follicles, large white follicles, small yellow follicles, and dominant follicles of low laying rate hens compared to the high laying rate hens. These results suggest that decreased IGF1 in the serum and follicles of laying hens was associated with the reduction in the egg production of aged laying hens. The present study provides novel insights into the endocrine changes in aged laying hens having different egg production performances.
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