You would think that having a love for animals would be sufficient to work in an animal shelter; however, much of the work we deal with involves working with people. A high school level of education is sufficient, but I have watched employees struggling with simple math.
I would suggest that you offer an examination that tests applicants on people and math skills. It is not necessary that a person loves animals to be in our field, they just need to appear that they love animals in all that they do.
I always told my staff that when dealing with a person, pretend that they are talking with the Mayor. When dealing with an animal, pretend that they are dealing with my pet.