Chicken feed can cause stones in goats, in males this can be fatal while in females it isn't as big of a deal but can cause some minor issues depending on the amount of stones she has. Males have a very complex urinary system which usually leads to the stones not being able to pass through the system. The stones usually end up causing a blockage which means urine can't pass through. The biggest issue with stones is that there is no exact cure, there are only things that you can try and are forced to just hope for the best. Cures can include ammonia drenches, lemon juice cocktails, potassium citrate capsules, and surgery, but even surgery isn't even a great cure as surgery only buys time for the animal, it doesn't really fix the problem. It shouldn't be an issue as they only ate it twice, but in the future be extra careful on which food you feed them just to make sure none of your goats fall ill. Stones are a pain, not only for you but for the goat especially. I unfortunately lost one of my boys in the summer because he got into the chicken feed one to many times and he just had to many large stones. My other boy luckily made it through, so there are success stories out there, just not as you many as you'd think.
I know I'm a little late but I thought I would just see if that would help you out any. I had to go through it once and I would hate for anyone else to have to go through that as well!