Physiological and endocrinological mechanisms associated with ovulatory cycle and induced-moulting in the domestic chicken - a review.

摘要

The ovulatory cycle and moulting are associated with physiological and endocrinological mechanisms involving a complex interplay of light stimulus, hypothalamus, pituitary, gonads, thyroid and adrenal glands. During ovulation, the LH surge triggers the release of a mature follicle. With advance in the age of a laying hen, egg production decreases coinciding with decrease in ovarian steroids and gonadotropins. Moulting occurs when oestrogen, progesterone and luteinizing hormone are low while thyroid hormones and corticosterone are high. The physiological processes observed during induced moulting are common to those found in natural moulting. Moulting results in the rejuvenation of reproductive tissues of old laying hens, preparing them for another laying cycle. Vitellogenin provides the two proteins (lipovitellin and phosvitin) to the developing yolk, at the same time serving as their transport protein through the blood stream. Low levels of vitellogenin in the plasma of moulting hens are attributable to decrease in oestrogen during moulting since production of vitellogenin from the liver is stimulated by oestrogen..