The situation re: straw is complicated.
Our usual source of chemical-free straw has run out this year; we have managed to find one last pallet of 40 bales of chemical-free, which will just about see the cattle through the winter if we are not profligate with it. So none to spare for greedy, mucky Davy, who would eat / dirty / use half a bale of straw a day, on top of a hay ration.
I don't mind so much if the ponies get straw that might have had chemicals on it - we don't eat them or drink their milk

, and the amount of chemicals which would be persistent through composting and survive to get back on the fields or veg plot is minimal, given that aminopyralid is not authorised for cereal crops - but because there are a gang of us looking after the animals, most of whom are not experienced, it's just impossible to keep the two lots of straw in the barn and not have the wrong one end up in the cattle pen. (People sometimes bed with hay, get hay and haylage mixed up...

.) I'm hoping that the chopped bedding straw will look sufficiently different - itself and its packaging - that mistakes won't be made, plus the company that make it are very environmentally aware and source carefully, so whilst they can't 100% guarantee the crops would have had no treatments, the odds are somewhat better than with any other source.
The hay we use is locally produced from untreated ground. Some people would think it poor hay, but it's perfect for the ponies; the cattle get half hay and half home-made haylage and do well on that. The sheep are mostly Shetland mixes so they are fine on the rough hay. Anyone who needs a bit more gets grass pellets.