I believe what complicates an animal abuse case is that horses...or dogs, cats, cows, whatever...are considered property. Even a criminal can regain his/her property, once that person has paid the fines or served the time. If the horses had been children, there would have been no delay in removing them and placing them in a safe situation. I'm fairly sure that the courts are far more reluctant to let anyone who has abused a child have custody again...and the law backs them up. As Fox Hill points out, the laws regarding animal abuse need to change. Living creatures need to have different legal standing than inanimate objects, with more protection from future abuse by their former owners.
The laws vary. On "Animal Cops Houston" the judge is always taking horses away from abusive owners. . And agreeing not to have animals can be made a condition for avoiding jail, or for a shorter sentence.