There are no such rules for emotional service animals. There are different types of animals in different shape and sizes and species can participate in this program. If you have a pit bulls and want to know can pit bulls be emotional support animals or not, then search the net https://docs.google.com/document/d/1PXG6JUx4sHv4S5xLVivInYp1tO9BwvOL_vOY2NCZVjQ/edit?usp=sharing