It would definitely be advisable to scale up the Porcupine caribou herd and also bring in several males.We have 9 female caribou but I know its a mix of mothers and daughters so some may be too old.
To put it more bluntly: caribou are endangered and populations are diminishing and areas of distribution - particularly in the Mid West - is receding northward. The woodland caribou is in dire straits (much like the Eurasian forest reindeer). It should be a North American ex situ priority for zoos over domesticated reindeer!