How much milk thistle should I give my pets?

I was told since I give my dogs 13lb and 17 lb a heartworm preventative that I should give them milk thistle afterwards for approx 7 days to help with there liver. If this is true how much

"The standard dosage of milk thistle extract is based on a silymarin content of around 80 percent. Most supplements of milk thistle contain about 100 to 200 mg of the herb.As mentioned above, milk thistle is very safe on dogs. For dogs with advanced liver disease, a dosage as high as 200 mg per 10 pounds of body weight is possible. For other liver problems or health conditions, 75 to 100 mg per 10 pounds of body weight per day is sufficient to see results.If milk thistle causes upset stomach, gas, or mild diarrhea in your dogs, simply reduce the dosage."So for your pets, I would probably start with 75mg for small dog and 100 for bigger. If gets upset stomach, lower the dose. This is assuming there is no liver disease. If there is a liver disease, I would do 200mg for small dog and maybe 350-400mg for big dog (I'm assuming). You know what I would do? If my vet told me to use milk thistle, I'd ask them how much. From what I am seeing though, milk thistle is mainly for liver cleanouts and liver disease. I use heartworm preventatives for my pets and have NEVER used milk thistle.