A model of follicular development and ovulation in sheep and cattle

A dynamic model to describe ovarian follicular development following commit ment has been developed, It identifies follicular growth with oestradiol pr oduction and assumes that this growth is the result of intra-ovarian stimul ation. gonadotrophin stimulation and inhibitory interactions among the foll icles, where larger follicles suppress the growth of the smaller follicles. The variables of the model are the levels of oestradiol in each follicle a t commitment, the rate of change of oestradiol production by individual fol licles during follicular development, and the level of oestradiol that will induce luteinizing hormone (LH) surge. Changes in the variables of the mod el could be associated with both genetic and environmental effects. The beh aviour of the model is consistent with experimental observations. The model can be expanded to include exogenous follicle-stimulating hormone (FSH) ad ministration assuming that FSH is associated with advancing the maturation of gonadotrophin-dependent follicles without affecting the number of commit ted follicles. The use of the model to explore FSH administration strategie s is demonstrated, The model confirms that the response to FSH administrati on depends on both the amount of FSH and the time of administration. The la rgest number of double ovulations occurred when FSH was given at the time o f the deviation of the dominant and subordinate follicles. (C) 2000 Publish ed by Elsevier Science B.V. All rights reserved.