Film about mad cow disease, all ending in Ohio, say (7)
I believe the answer is:
midwest
'in ohio say' is the definition.
(Ohio is part of the US midwest)
'film about mad cow disease all ending' is the wordplay.
'film' becomes 'mist' (to film over is to mist or fog over).
'about' indicates putting letters inside.
'all ending' indicates one should take the final letters (multiple final letters).
The final letters of 'mad cow disease' are 'dwe'.
'mist' going around 'dwe' is 'MIDWEST'.
(Other definitions for midwest that I've seen before include "Mist dew (anag.)" , "north central US" , "Region from Ohio to the Rockies" , "North central region of the United States" , "Area from Ohio to the Rockies" .)