Yes they are. Under normal circumstances they wont eat them, but if they are unfamiliar with them or if the area gets overgrazed they may browse on them. I have a line of azaleas along a fence but my cows never eat them. There are also native azaleas growing on the farm that the cows dont eat. pretty much anything a cow doesnt eat is poisonous or either has thorns.
Yea I was going to put a sign by Black cherry trees in the pasture so the cows would know not to eat them. I have two huge cherry trees in the pasture betwwen hogs,cows, and birds if you want a cherry you better catch it on the way down.