I've personally seen more problems created by over trimming of the bars than not trimming. Soles dropping due to no support etc.  My horses rarely get their bars touched...they've shed them off as they've fully transitioned.  I've found that excess bars are most critical on foundered horses that already are sensitive to any pressure.  Even a frog that overgrows can be too much for them.  Those horses I keep the bars trimmed to just above the sole.

 

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