Are suckling pig tails a source of protein? (3)
I believe the answer is:
egg
'a source of protein?' is the definition.
'are suckling pig tails' is the wordplay.
'tails' says to take the final letters (I've seen 'tailed' mean this).
The last letters of 'are suckling pig' are 'EGG'.
(Other definitions for egg that I've seen before include "Breakfast food, perhaps" , "Incite; ovum" , "Bird's first home" , "Yolk and white in a shell" , "On the face, its an embarrassment" .)