5% is the maximum allowed conc of DMSO given orally to experimental rats

The IACUC at your university should indicate an allowed DMSO concentration if there is one. 

Most institutions don't allow DMSO to be dosed at all because it's so toxic, only in-vitro/ex-vivo.

I'm assuming you need it for formulation because whatever compound you're using won't go into solution without DMSO.