Very simple suggestion. Currently WorkGiver_Tend applies to both animals and humanlikes. If you want to have a different WorkGiver for animals and human colonists you need to make an assembly and all that jazz.
My suggestion is to have at least 2 giverClasses like WorkGiver_TendHumanlike and WorkGiver_TendAnimal so we can make their WorkGiverDefs higher or lower on the priority list with mods.