Excerpt from this article on DogAware.com Health: Caring for Dogs Before and After Surgery
which recommends stopping supplements a few days before and after surgery:
You should stop most supplements a few days before the surgery, and maybe for a day or two after, as many of them can cause bleeding, including fish oil (salmon oil), evening primrose oil, borage oil, garlic, ginger, vitamin A, high-dose vitamin E, and white willow bark. Chondroitin may also increase bleeding, but glucosamine apparently does not. Bromelain and other proteolytic enzymes may also increase bleeding. MSM apparently can occasionally act as a blood thinner as well. Herbs that can cause blood thinning include alfalfa, chamomile, ginkgo biloba, ginseng, hawthorne, meadowsweet, dong guai, turmeric/curcumin, bilberry, feverfew, red clover and some mushrooms. See When Herbs and Surgery Don’t Mix for more info.
In addition, high doses of Vitamin C may interfere with anesthesia, so again, best to discontinue for at least a day or two before surgery."
If you plan on giving milk thistle for detox & your dog is on heartgard, this article discusses milk thistle and heartgard: