I have been given a booklet published by William Cooper and Nephews, Agricultural Manufacturing Chemists Berkhamstead., their 1916 catalogue. The photo of their price list makes interesting reading.
Nice to no they got cared for, makes sense they obviously was valuable assets and not cheap !
Prints in image below . We have came across sections which are still a few inches deep & represent almost motorway junctions . Can find photos if of interest.
I doubt the original contents would have been for the ponies, mastitis is primarily a cow udder complaint and IIRC is spread by flies. Possibly the bottle was re-used though, if it's graduated for dosing then possibly some other concoction was put in it.
Yes, pit ponies were looked after - as you say, they weren't cheap and needed to be properly cared for if they were to work well.
Stockatrice is certainly an animal veterinary product. Seen here with dose graduations. A more collectable version comes in emerald green. Its quite possible it was used again for something else. Date probably c 1910.