Congratulations on buying a big boy! The issue you're likely running into is the NPC item stacks cap, which is considerably fewer than what player characters can manage.
Try taking some of the low-weight items from your bull and start prioritizing heavier loads when needed. You can check his weight capacity with slender trunks, stones, and then rocks to find an exact figure. I have a habit of appending the names of my pets with their weight as a reminder.
Consider buying a sheep or pig to offload those smaller items until you find a suitable spot for hoarding these hunting goodies.