wheel bearing question?

I have an 09 rancher at, and i took my wheels off today to try to pack my wheel bearings???? Im confused I thought you were supposed to pack them every year or so, but they looked like sealed bearings....me and my dad both just scratched our heads and put the wheels back on until I get some more information on it.....does anyone know, or has anyone done this before? I bought some expensive amsoil water resistant grease for atvs and now I dont know if i can use it....if it matters i do ride in alot of water, mud and sand...mainly water though