Diet will tighten the white line not trimming.
Many whitelines are stretched only due to improper trimming, having nothing to do with diet. NOT ALL WHITELINE ISSUES are 'diet related' . It gets so frustrating to hear this misinformation so often.
That said, THIS horse does not even have a whiteline issue. What is has is piles of dead sole which eventually would have to crack out if not trimmed. So it naturally is no longer attached to the wall beyond the REAL sole. Once trimmed the trimmer will find a nice attached white line and tight connection, Guaranteed.
I have done only about 50,000 sets of hooves (maybe more) so I think I can say this from what I see here with confidence. There is a nice foot hidden under there and diet has nothing to do with it in this case .