Definition of pro-oestrous in English:
pro-oestrous
(also proestrous)
adjective prəʊˈiːstrəsprəʊˈɛstrəs
Biology That precedes oestrus; of, relating to, or in the phase of pro-oestrus.
Origin
Early 20th century. From pro- + oestrous. Compare pro-oestrum, and slightly later pro-oestrus.