An ear tag for marking animals includes a female portion consisting of a female head optionally borne by or formed in a first panel, a male portion consisting of a male punch optionally borne by or formed in a second panel, identifying means being borne by at least one of the male or female portions. The male punch is configured in two separable elements, one of which is housed in the female head and the other forms an organic matter sampling device during the passage of the male punch through the ear of an animal, which is moveable in an axial channel thereof and is withdrawn through the panel of the male portion after fastening the tag onto the animal's ear.