Hi,
I just shot my first red-deer. It was a funny chase but after the loot i noticed i could barely move… seems that that single deer gave me 87 red-deer venison… adding a whopping 45 weight… i’m guessing this is a bug? 
That is not a bug. This is working as intended.
In the Middle Ages nothing could be wasted!
500g packages 
A full size healthy deer(depending on the species and food and minerals in its range) can weigh 100+lbs (45-50kg)