I’d cut back on the kale and see if that makes a difference.

I’d second @bam. From what you mentioned, kale seems to be the only difference in their diet so that’s most probably the culprit.

Poop weirdness is not an emergency. True diarrhea is, but true diarrhea isn’t about a bit of slimy poop or excess cecals/mushy cecals. Diarrhea when there’s ample watery or mucosy runny stools.

This sounds more like a slight disruption in the GI microbiota. It could be that the buns’ tummies are having a little bit of a difficulty processing kale and that the introduction needs to be done more slowly. Or maybe kale just isn’t right for your particular buns.

I always try to provide a couple of different greens every week in addition to the spring mix base for Panda and Fernando. Last week, for example, it was parsley, cilantro and carrot-top greens; this week, they’re getting watercress and dandelion greens. I think I’m going to get arugula and romaine hearts next week; Fernando is particularly fond of the “woody” stems of romaine and will often grab a piece of romaine stem from the bowl, scamper off and nosh on it to his heart’s content.