Perhaps writing milk-producers' guides (7)
I believe the answer is:
rudders
'guides' is the definition.
Although both the answer and definition are plural nouns, I can't understand how they can define each other.
'perhaps writing milk-producers'' is the wordplay.
I cannot quite understand how this works, but
'writing' could be 'r' (one of the traditional three R's of education) and 'r' is located in the answer.
'milk producers'' could be 'udders' (I've seen this before) and 'udders' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for rudders that I've seen is " Nautical steering mechanisms".)