So the question now is there a case for the injury itself, or just the unlawful job termination?
I am guessing everything happened in Texas. If so, then all Texas laws, including equine, would be in effect. As to which may be applicable to this situation, only a lawyer could answer that.
More to the point, it doesn't matter which laws may apply. What matters is if you have a case. For practical purposes, you only have a case if you have a lawyer willing to take it on. :) In other words, you need to find a lawyer and explain the entire situation in detail. At that point he/she will tell you if you have a case, what it will cost and what outcomes are possible.
In many states, it is difficult to evict someone from their residence. Even in cases where a renter owes back rent there are specific procedures that must be followed. It often takes many months to remove a tenant from their living space.
At a quick guess, I would think that avenue (sold the trailer and evicted the person without notice) provides one good direction to take. Of course, it depends on Texas law among other things.
This advice is worth exactly what you paid for it. Just like any other advice you would get on the internet. :) With the vague description you provided here (and it would be BAD idea to post more details, especially if you plan to pursue legal action) even a real lawyer would be unable to answer your questions.
You need to sit down with a local lawyer who knows this area of the law. Many will provide a free consultation to tell you if you have an actionable claim.