Before the houses were closed, the International Fund for Horses pegged the number of slaughtered horses in USA at 65,000/year. The American Horse Council pegs the amount of the horses currently in the USA to be over 9 million. That's fewer than 1% of the horses in the states being slaughtered each year. Abuse becomes more evident now that we don't have a "disposal" system for these abused horses, but it is not new. This has been going on for years and it will continue to go on with or without slaughter. There is no major outbreak of these neglected horses because slaughter in the USA was closed.

This happens to all stock animals. Cows, horses, pigs, etc., it's just a society that can peg an animal as a pet worth fighting for, and a commodity not worth the fight.