An oestrus detection device comprising an indicator carrier of flexible material which is adapted for attachment to the top rear central section of an animal between its hip-bones. An indicator is detachably mounted on the indicator carrier, and is made of flexible coloured flowable material connected through a fine orifice to at least one channel. The construction and arrangement is such that when the indicator-mounted carrier is mounted on a cow or other female animal and mating technique by a second animal is made, pressure applied by the second animal upon the sachet forces the differently-coloured material to flow along the channel or channels of the indicator for observation by a farmer.