pro-oestrus
/prəʊˈiːstrəs/ /prəʊˈɛstrəs/(US pro-estrus) Biology
noun
The phase of the reproductive cycle in female mammals immediately preceding oestrus, characterized by the growth of ovarian follicles and development of the endometrium.
Origin
Early 20th century; earliest use found in Proceedings of the Royal Society of London. From pro- + oestrus.