PARASITES are the #1 killer of goats. This includes coccidia, which is a single-celled parasite. It has taken several years of study and experimentation to come up with a regime that works for my herd to keep the parasite issue at bay (the pic is the 500 ml bottle of Valbazen in my meds cabinet with an expiration date of more than three years ago, that's how little I use it). I'll share my regime, and I'd like to hear from others who have anti-parasite advice.
The typical goat parasites travel the oral/fecal route, so keep a CLEAN farm: a clean dry barn, construct feeders that don't allow hay to fall on the ground, set water tanks up on blocks to prevent urine and feces from getting in the water, utilize pasture rotation and either prevent stock from going out on dew-wet grass or make sure they have hay to keep them occupied long enough for dew to dry, have a dry lot (a lot where no grass grows and it never gets muddy), add tannin rich forage to their diets (such as sericea lespedeza, oak leaves, etc), kid pens are especially important to keep clean and dry (I use a thick straw bedding which is removed/replaced weekly). Walk your barn DAILY and look at the poop! If you find "clumps" or "logs" that's a clue. Check those eyelids and haircoats. I offer loose minerals and kelp, free choice. They also get 5cc of Replamin Plus gel orally once a week, and copper bolus every 4 months. The largest number of adult goats that I have had at one time is 62. If you have 100s of goats, I especially would like your input. Goats are normally very clean and picky eaters. If you are too busy to take care of them, you may need to re-evaluate exactly why you have them.