Abstract
Publisher Summary This chapter discusses the hypothalamo-hypophyseal sensitivity to central injections of progesterone (P) and LH-RH in the laying and molting hen. Injection of LH-RH at a time 15 to 10 hours prior to the C1 ovulation induces secretion of LH, testosterone and estradiol, and premature ovulation. In addition, injection of 500 μg progesterone 14 to 12 hours prior to ovulation induces a preovulatory surge of LH, those results in the endogenous secretion of P, and induces premature ovulation within 8.5 hours of the time of injection. Centrally-injected LH-RH was effective in inducing premature ovulation, and LH, P, and T profiles were similar to those in hens induced to prematurely ovulate with 20 μg P. It is speculated that although the preovulatory surge of P may play a role in the initiation and/or stimulation of an LH surge, the ultimate ovulation-inducing stimulus is some threshold level of plasma LH which was not realized in the hen. It is concluded that in the molting hen, pituitary sensitivity to LH-RH is maintained, as evidenced by the ability of LH-RH to induce an LH surge comparable in magnitude, but not duration, to that in laying hens, whereas hypothalamic and/or pituitary sensitivity to P is decreased or absent.
Published Version
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