When slavery was legal and the norm in the south, just because you treated your slaves well didn’t extend any freedoms or rights. It just meant that they experienced a level of captivity which was better than many others’ in captivity. Still, they were slaves, captives, subject to the whims of any white person around them. According to most accounts slaves were considered the same as livestock.
In that context let’s look at our horses. They are subject to whatever whim we should have. We buy/sell/trade them as we wish (or the market will support). When they are no longer useful we can put them down, send them to auction or the slaughterhouse. If they misbehave there are torture devices to deal with that – from whips to spurs, harsh bits and even some trainers have been found to use electric cattle prods on their horses.