The period in the estrus cycle preceding estrus, characterized by the growth of the graafian follicles and physiologic changes related to estrogen production. SYN: proestrum.
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pro·es·trus -'es-trəs or pro·es·trum -'es-trəm or chiefly Brit pro-oes·trus or pro-oes·trum -'ēs- n a preparatory period immediately preceding estrus and characterized by growth of graafian follicles, increased estrogenic activity, and alteration of uterine and vaginal mucosa
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pro·es·trus (pro-esґtrəs) [pro- + L. oestrus] in female mammals that have estrous cycles, the period of heightened follicular activity preceding estrus. Called also proestrum.Medical dictionary. 2011.