Fecal matters

Hi there, Love your site!  You're what helped us make the leap last year to raw, my finicky stomached boxer cross and I thank you so much!!  I have a question about poop, to put it frankly.  We've been on raw for about a year, maybe a little less.  In the last month or so, I've noticed our dogs starting to strain a little while pooping, not excessively, but noticeable.  When observed a little more closely, it's almost like they're pooping dust!  It's not fully formed at all, just, for a lack of a better descriptor, dusty looking.  But it's not every time either, just starting to happen more often.  Leading up to this, they would poop fully formed, then it would turn white and crumble. Is this a too high meat/bone to veggie ratio build up?  Or a lack of offal?  They're in perfect health otherwise, no issues noted, they're eating and drinking fine, so no illness we're aware of, and they receive fish oil everyday.  Any thoughts would help!