Space Cowboy by Justin Stanchfield
On the remote planet of Aletha Three, a genetically engineered creature with the unstoppable killing instinct of earth's most ancient predators has begun stalking the struggling population. Armed only with his dad's old rifle, cowboy Travis must find out where the predator came from and how he can stop it - before it gets a taste for people, instead of cattle. Filled with danger and excitement, cowboys, spaceships and nightmare creatures, Space Cowboy is everything a boy could want in a book.