Sheep can eat tansy. Yes they can. It’s true. Just stop arguing with me on this one, they really really can eat tansy. Even the USDA recommends using sheep and goats to suppress tansy, in this article, down at the bottom, and OSU states that sheep are ‘not susceptible to Tansy Ragwort poisoning’ in this article.
Anecdotally speaking, the breeder we purchased our ewes from used to work as a researcher at OSU for 20 years, during which time they ran a small experiment where they pelletized straight tansy and fed it to lambs. Upon butchering they necropsied their livers, just to find them to be perfectly normal. There is also the fact that our sheep have been devouring tansy for years with no ill effect.
Tansy is an herbaceous biennial, with an unpleasant bitter odor, and apparently a rather unpleasant taste. Interestingly, it seems to be a bit like coffee or beer, because most animals, sheep and goats included, do not care for it until they are forced to eat some. Once they acquire a taste for it however, they will then seek it out first in a pasture as their most favorite treat. I promise, our sheep are fine.
The unfortunate part about using sheep to manage tansy, is that if you do not pull the root system and it does not get to go to seed, the plant will come back, however if it is continuously grazed or cut it will eventually die. Which, if you have spent your summers in the blazing sun, breaking your back pulling tansy, you will realize it is worth the somewhat delayed results. Grazing flower heads at a minimum will prevent spreading seed, and keep your neighbors from hating your guts.
Many people find success spraying toxic herbicides to control tansy, but for organic producers, or just those concerned for environmental and personal health, sheep are a much pleasanter option. The other concern with herbicidal control is that it tends to kill legumes which benefit pasture health and the grazers the pasture is intended for.
My last enticement to sheep is their pleasant nature and ease of containment. If you have had goats, and are expecting sheep to be much the same, let me assure you, they are NOT. Goats are hell-spawn in comparison, and that’s coming from someone who voluntarily chooses to own them. While sheep offer their own management challenges, such as lambing and winter foot issues, as an interested party in leasing summer pasture to a flock of tansy eaters, you would only have them around during their easiest and most pleasant season. So there you have it. If you have been ripping your hair out in addition to thousands of stalks of tansy, give your local sheep farmer a call and see if they have some ewes for you to borrow. (p.s. They of course would have to be accustomed to eating tansy already, otherwise they will make me a big fat liar, as they so carefully graze around the tansy like your horses and cows already do.)