If the farmer has dried the grain in a grain dryer at normal temperatures (hotter than mid 30'sC) then the seed is dead and it won't germinate. So it would be pretty useless for malting.
Also, feed barley or barley that isn't grown for malting is usually high in nitrogen and will: throw a haze in the finished beer (there are ways around this - e.g. using maize, rice etc in the mash); it will heighten mouthfeel on the final beer; it will darken the beer (that's why most rustic farm beers are orange!).
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