What about nonfat or lowfat milk?

I don't think it matters if only using as a "poaching" liquid. If you are using the liquid after to make a sauce or something else, it might make a difference. Also I would look into the added liquid injected in the chicken breast, most grocery stores add water or a salt water mixture to the breast to make it less dry when cooking it. It should say so on the package. You may pay less per pound but the package will state that up to 5% is "liquid added" or something similar.