Maybe the druids were waiting for the tigers and deer to die of old age... and only then did they take the horns (hooves, hides)... has anyone considered this option?
How many druids are there, and what is the weekly increase in their numbers?
Let's call it a controlled process of creature demise.
Extermination...
And when building the Grail, a plague attacks the deer, and 50% more of them die... :D