A tag for attachment to an animal comprising: a transmitter unit for generating a transmitter signal; a first antenna unit connected with the transmitter unit, for emitting the transmitter signal; an energy source for providing electrical energy to at least the transmitter unit; and a housing in which the transmitter unit, antenna unit and the energy source are included, the housing being provided with an attachment opening for receiving therethrough an attachment element for attachment of the tag to the animal, characterized in that the first antenna unit is provided with at least one first winding which extends around the attachment opening.