I have had the same reaction to the video as other posters, I remember the previous thread where it was posted.
However, I think the OP has linked two hot button topics that I'm not sure it makes sense to link.
The video shows out and out sociopathic animal abuse. Not neglect, not from ignorance, but agressive, malicious abuse. The fact that it occured at a dairy barn is mostly coincidental; the abuse itself has nothing to do with dairy farming as a practice. Dairy cows in general have a pretty nice life while they're producing.
Horse slaughter, and other forms of livestock slaughter for food, *are* part of farming practice. We raise cows, pigs and chickens for food and a farmer must do so in the most cost efficient way possible. While Americans don't consume a lot horse meat as food, the fact that there are slaughter plants in Canada and Mexico is because there is a demand for horse meat, and that we have a huge supply of unwanted horses to fill the demand. If slaughter for food consumption is not done quickly and humanely, or if the animals aren't raised or transported in an acceptable ways, we can address that in a number of ways.
The solution to that horrible video is criminal prosecution for the abuser.
The solution to ojections to horse slaughter and livestock slaughter for human consumption is legislation on farming practice and slaughter conditions, and educating consumers to create a demand for cruelty free, organic, grass fed or free range meats or to limit demand by encouraging vegetarianism and veganism.