or  pro*es*trum  or chiefly Brit  pro-oes*trus  or  pro-oes*trum  n :  a preparatory period immediately preceding estrus and characterized by growth of graafian follicles, increased estrogenic activity, and alteration of uterine and vaginal mucosa .
 
 
 
Similar sounding terms:  pro·es·trous 
 
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