PEU – entry 386.7 noun + ‘s + noun: cow’s milk; a hen's egg
The 's structure is often used for products from living animals.
cow's milk
sheep's wool
lamb's wool
a hen's egg
(BUT camel hair, horsehair)When the animal is killed to provide sth, we usually use noun + noun:
calf skin
chicken soup
chamois lether
a lamb chop
fox fur386.10 noun + noun, noun + ‘s + noun, or preposition structure?: This is a very complicated area of English grammar. The 'rules’ given above show the general patterns, but unfortunatelly there is no easy way to be quite sure which structure is used to express a particular compound idea. The most common expressions will be learnt by experience, in cases of doubt, a good dictionary will often show which form is correct.
Díky! To jsem myslel.