Hi Andy-I have 2 springer spaniels. We fill up 2 water bowls (I use reverse osmosis now-we invested in a system last year) and I put 1 -2 drops of Lugol's in one bowl and none in the other. My older boy (10) ALWAYS goes for the iodine. My girl (2.5) hardly ever does.?? Anyway, I initially put in up 5 drops and my boy was always in the water. And then he started getting a little skinny and I backed off. He is now nicely lean. I also give them vitamin c, fish oil, glucosamine/chondro and half a brazil nut (every other day on the last one). I feed a good quality dry dog food, but I am almost always supplementing with meats, oils from meat (bacon) or coconut oil. They love it and are very healthy.
On a side note, for those of you who have dogs with eye problems, you might try some Colloidal Silver eye drops. Works for many things with pets.