A mixture model to assess the effect of hormonal stimulation on the development of follicles in prepubertal heifers

Philippe Lambert

Journal of the Royal Statistical Society Series C, 2002, vol. 51, issue 4, 405-420

Abstract: Summary. The goal of this study is to assess the effect of follicle stimulating hormone (FSH) on the growth of follicles in prepubertal heifers. Adams and co‐workers have shown that follicles develop in waves as in post‐pubertal heifers: after a few days, a dominant follicle arises on one of the two ovaries whereas the other subordinate follicles regress. The dominant follicle remains detectable when the next wave occurs. The number and the diameters of these follicles have been measured for 14 days. The same experiment was repeated after a 3‐day FSH stimulation. Several large follicles now arise simultaneously on both ovaries together with small follicles which cannot be detected any more when the next wave occurs. Unfortunately, follicles were not individually tracked. Therefore a three‐component mixture model was used to describe the potential simultaneous observation of dominant, decaying dominant and subordinate follicles before the FSH stimulation; the same type of model was considered for large, decaying large and small follicles after the hormonal stimulation. Moreover, for technical reasons, only follicles larger than 2 mm are observable. Measurements were thus left truncated. The models fitted are used to quantify the effects of the stimulation and to determine the ideal time point at which follicles should be punctured under ultrasonography to harvest ovocytes that will be fertilized and cultured in vitro .

Date: 2002
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