Dairy cows, jumpers are popular (7)

I believe the answer is:

jerseys

I'm a little stuck... Click here to teach me more about this clue!

'dairy cows' is the definition.
'Jerseys' can be an answer for 'cows' (Jersey is a type of cow). I'm not sure about the 'dairy' bit.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for jerseys that I've seen before include "They provide milk" , "tops" , "Close-fitting pullovers" .)

I've seen this clue in the Sydney Morning Herald.

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