Maybe just B12. Go to ibdkitties.net Lisa has a page written up about B vitamins
Well, it is thiamine, B-1 in the study that is showing up deficient. I have spoken to my vet about Vitamin B for Mazy cat (the one with the digestive problems being discussed elsewhere). She will not prescribe B-12 or B complex shots without testing levels first. Mazy is due for bloodwork in June and I have told her I want the added lab test to check her B levels.
I have a B complex vitamin (for humans) I was using to supplement with when I first started prey model raw. I stopped using it because it was causing Mazy to have trouble peeing. When she got the B complex added to her meal, the next morning when she peed she would hesitate and hesitate, and wince when the pee finally started flowing. So I stopped it.
Since Mazy takes pepcid on a pulse regimen (two weeks on, two weeks off) I am concerned about B-12, too. However egg yolk does provide a good amount of B vitamins, and she gets that twice a week, the other two get yolk once a week.
Anyway back to the topic, I've always tried (with the exception of mazy cat) to feed a wide vareity of brands and formulas for this reason (possible shortages or excesses in the foods) and also to avoid trouble when recalls happen, or foods get discontinued. But, again coming back to Mazy cat, for her, it's just not been do-able.
..Off to read the links on vitamins provided....