Yeah tell me about it, my bulldog is only 65 pounds and she's STILL a moose. I had problems with my old bully/boxer cross thinking it was okay to eat plants and had to keep her well away from my crops. I even considered hot pepper wax meant to keep deer away, haha!
Nah there's a farm supply in Greenfield MA that's good.
Horse manure is going to be problematic. There's 3 problems:
1- seeds. You may well find grass growing in your pots, lol!
2- pests.
3- Nitrogen too 'available'- fresh manure can easily burn plants. It shoudl be composted very well before use. Sitting in a compost heap that's watered, turned, and even inoculated with compost bacteria for at least a winter is ideal. Then you turn it onto a big BLACK tarp, fold it into a packet, and let it BAKE in hot sun for a couple weeks to kill bugs and pests. For indoor use, the bagged composts are a less troublesome product. Watch your plants for signs of N overdose as the roots reach the manure in those pots and be prepared to flush them really well.