"SO" in the name stands for "Struvite Oxalate," which are two common compositions of crystals that can cause problems in cats and dogs1. The cat food is designed to increase urine production in cats, which helps them expel dilute minerals from their urinary tracts and prevent the formation of crystals or stones3. The dog food promotes an unfavorable environment for struvite and calcium oxalate crystals and helps dilute excessive minerals by increasing urine production2