I found this on HGS and thought I would share.
Oddities often consumed by horses on pasture.
No problem, assuming fairly limited quantities and otherwise balanced ration:
Thistle (NOT Russian Knapweed or yellow star thistleCentaurea spp)
Sunflower seeds and plant
Wood/bark of most trees (NOT Prunus spp or black walnut or locust)
Potential problem if eaten in large quantities:
Astragulus and Oxytropis spp/(vetches and locoweed)
Most bulb type flowers (tulip, iris, etc.)
Wilted red maple leaves
Acorns/new oak leaves
Avoid at all costs (Lethal or severe toxicity potential)
Lily of the Valley
Tomato or potato plants
Rhubarb leaves and roots
Sorghum (Johnsongrass and Sudan grass)
Japanese Yew (all Taxus spp)
Pits of peaches, cherries, or avocados
Russian Knapweed or yellow star thistleCentaurea spp
Perfectly acceptable treats (fed in limited quantities (<1-2 lbs/feeding)
Carrots, apples, grapes
Dried beans, such as pinto, red, fava (however should be cooked or heat treated)
Mangoes (not the seeds)
Bread/bagels/cake (NOT if they contain chocolate or poppy seeds)
Potato chips and potato products
(do not give raw potatoes to pregnant mare it is toxic
gives them blood poisoning).
Rice products (not raw rice)
Hot dogs, hamburgers, tuna fish, ham or even roast beef sandwiches!
Most dog and cat foods
Beware large quantities, but probably acceptable in very small amounts (<2 to 4 ounces/day)
Cabbage, broccoli, kale, chard, collard greens, brussel sprouts
Rhubarb stems (NOT the leaves or roots)
Garlic and onions (large amounts may cause anaemia) When lower doses are consumed on a regular basis, or Large amounts are consumed this may cause anaemia...(the same goes for onions.... to much can cause anaemia).
Avocado (NOT skins or seeds)
Lathyrus spp. Beans (India)
Sugar candies such as jelly beans, gummy bears, peppermints, etc.
Safe in very limited quantities BUT WILL CAUSE POSITIVE DRUG TESTS
Morning glory plants
Willow leaves and bark
Tobacco (consumed, not inhaled)
Carrots in very large quantities only (over 5 lbs day)!
Persimmons (seeds also may cause impaction)
Chocolate in any form
Hot pepper/chilli flavoured products (Nacho chips, etc)
Non-decaffeinated coffee or tea in any form
Some dog/cat foods (Beware bakery waste as an ingredient-may contain chocolate)
There are obviously a wide range of things that our horses may enjoy consuming, not all of which are good for their health. Many horses would refuse to even sniff many of the items listed above. Knowing which potential treats are safe, at least in limited quantities, is important for horse owners. You never know what might be offered to your horse!