I have American Livestock Insurance.. which is Hartford Insurance. They have a website that has a lot of information, as well as forms you can download. Everything has to have a health certificate before they'll insure.
When you buy animals at a registered sale it's pretty easy to determine value, but that's something that you need to make sure you understand as well. They'll only insure for the purchase price.
Make sure you read everything! Most policys only cover death.. not long term sickness or if you put the animal down for humane reasons. And they are very specific about what you need to do in case of a loss.