How do I use sulphur powder in feed

Sulphur powder and tablets used to feature in many treatments from the past. The brother of one of my schoolfriends was given a course of sulphur tablets to combat rampaging teenage acne and then given carbon tablets to combat the evil smelling gas produced from his digestive system.

The barber I used forty years ago recommended a "spirits and sulphur" treatment for severe dandruff and scaly scalp.

Sulphur is used extensively as a dusting powder in horticulture to ward off all manner of attacks.

If you can find a veterinary surgeon with a long grey beard and a memory to match you have a very good chance of finding the information you seek. Most old vets, like most old doctors were also highly competent apothecaries.
Similarly a pharmacist of the old school was also a competent apothecary., being forced from necessity to manufacture his own remedies from cheap ingredients in working class districts to service the community.

Good luck!