The use of antibiotics with most sport horses is not very common/excessive. At least with mine. I've had horses for 4 decades (most of that was as a one horse owner) and I remember using antibiotics maybe a half a dozen times if that many. What I've used the most of would be NASIDs (non-steroidal anti-inflammatory drug), mostly phenylbutazone (bute) or banamine. A typical dosage for a 1000lb horse would be 1-4 grams a day prescribed for inflammation. These are not terribly different from ibuprofen for humans. The other drug/supplement that is commonly used are glucosemine products, at most 5cc a week for a loading dose then 5cc once a month. But again we are talking about a gram or two a day in 50lbs of matter to be composted. Parasites. Even with regular worming most horses carry a small amount of intestinal parasites. However, according to veterinarians most equine parasites won't survive a in a clump of manure on a day hotter than about 85 degrees. They are more resistant to cold weather. I don't really know how to answer the herbicide in hay question. Most horse owners won't have any idea what was used for broad leaf weed control for their hay. I can say this: 2 4-D is the most commonly used broad leaf weed killer for agricultural in the world and I'm pretty sure it is not of the class that might be an issue. It is the herbicide I use when needed on my own pastures used for grazing and is the herbicide most people I personally know who grow hay use--including the source for my own hay. I've never run across anyone in my horse circle who has used their own composted manure/stall leavings and been anything other than thrilled with the results. So I would guess that the problem is on the untypical side of things and seeing my own results, worth the risk.

Thanks, everyone! Barb, I've collected numerous bags from Starbuck's so far but they don't save it regularly... they throw it all away!!! What a travesty! I did a little research and dbm2009 is right that adding already composted material will provide more of the micro-organisms that break stuff down. tiffy_z5_6_can, I'm in Atlanta... Unfortunately, I'm about four hours to the beach or else I'd be all over the seaweed!!! I did, however, find a horse rescue farm nearby that gives away manure for free!!!! Heading there tomorrow to pick up a few bags of it. My wife is thrilled!!!

folks just a tip,i use for my tomatoes, i have all raised beds,i take a 5 lb,coffee can drill holes into bottom one qtr about 8 then put in rabbit manurecouple hands full,then some leaves cut over with lawn mower twice then wet it, then put some straw on top wet it, screw on lid, put into soil about 4 inches,leave for spring i usally check 2 or 3 times before if some room i add coffee grounds, under straw, now by spring lotsssssss of worm poop now i dig hole with post hole digger add about half can to each hole, put in 2 tea spoons of epsom salt wowwww the toms i get close to record here in ga on one plant had 81 lbs, oh when can empty redo this set can filled back in a new hole when worms u dumped ready they will come right back this way no getting worms out of poop,lol lol im a little lazy lol tu happy gardening

Isn't composting (heating up and breaking down material) supposed to break down that kind of thing?