FR-600201 DE-4702086 The Domestic Goat

The domestic goat (Capra aegagrus hircus) is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe.

French peasant milking a goat in the high mountains

The goat is a member of the family Bovidae and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over 300 distinct breeds of goat.  Goats are one of the oldest domesticated species, and have been used for their milk, meat, hair, and skins over much of the world.

3 Greek goats

Female goats are referred to as "does" or "nannies", intact males as "bucks", "billies", or "rams" and their offspring are "kids". Castrated males are "wethers". Goat meat from younger animals is called "kid" or cabrito (Spanish), and from older animals is simply known as "goat" or sometimes called chevon (French), or in some areas "mutton" (which more often refers to adult sheep meat). Source: Wikipedia
The first postcard came from David (19 November 2015) Postcrossing and shows a French peasant milking a goat in the high mountains.
The second postcard showing three goats was bought in Greece but mailed from Germany by Britta (25 November 2015) Postcrossing.