Dog needing some sort of protein (7)
I believe the answer is:
pointer
'dog' is the definition.
(I know that pointer is a type of gun dog)
'some sort of protein' is the wordplay.
'some sort of' is an anagram indicator.
'protein' is an anagram of 'POINTER'.
'needing' is the link.
(Other definitions for pointer that I've seen before include "under control of mouse" , "Suggestion" , "Hint (for a dog?)" , "Indicator" , "Gun dog" .)