Current variability in superovulatory response prevents the economical production of large numbers of high quality embryos and limits the use of embryo transfer. Pulsatile administration of GnRH (gonadotrophin releasing hormone) elicits pulsatile secretion of LH (luteinising hormone) while chronic treatment with a potent GnRH agonist reduces LH secretion. Using the latter, gonadotrophin-dependent preovulatory antral follicle development may be suppressed, resulting in a uniform cohort of small antral follicles in the absence of a dominant follicle which could then be superstimulated by exogenous gonadotrophin.
The ovarian status of the donor animal before and at the time of gonadotrophin treatment appears to be a major determinant of superovulatory response in cattle. Transrectal ultrasonography is a non-invasive means of assessing the morphological status of the ovary which can be used on a repeated basis. Detailed evaluation of ovarian status by this means may enable superovulatory treatment protocols to be devised which are tailored to the individual donor animal. This possibility was evaluated in a preliminary study reported here.
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