Any reason the R key would not work? Latest version of Pixelmon with the recommended version of Forge.
No other mods installed that are in the official conflicts list.
3.5.1 - 1.7.10 - Recommended
Incidentally, I notice that the Issue Tracker link on pixelmonmod.com is not working:
http://forum.pixelmonmod.com/tracker.php <-- hostname does not resolve
Tracker is working: http://pixelmonmod.com/tracker.php?p=2
If R isn't working, make sure that you have spawn animals on in config and then check that the keybind is correctly assigned in options