Question: If you have don't have comprehensive coverage and you hit a farm animal (cow) in the middle of the road and find that the farmer has no insurance, can it be covered under collision?
Answer: No, an accident with an animal, such as a cow, is a comprehensive auto insurance claim, and if you don't have that coverage as part of your car insurance policy, you can't instead go under collision coverage.
Collision coverage pays for most incidents where you collide with something, be it a car, fence, house, etc. However, striking an animal (or it striking your vehicle) is covered by comprehensive coverage only, not collision. So hitting a cow, deer or even bird is a comprehensive claim. (A deer collision is by far the most frequent claim.)
If you are without comprehensive coverage, you can't shift an accident with an animal to be a collision claim. You are without coverage for the incident and have to look outside your car insurance policy for the cost of the repairs (or total loss) of your vehicle.
If you have already found out that the farmer is without any insurance that would allow you to make a claim against him, then you'll probably have to go after the farmer personally for the cost of your vehicle's repairs.
You may wish to contact your state's insurance regulator to see if there are any other options available to you or if you will have to seek legal counsel to go after the cow's owner.