Dog food used to be made with horse meat before the 1970s.
However around and after 1970 the use of horse meat in dog food was banned.
So dog food no longer contains any horse meat in it.
Dog food today typically contains hamburger, pork and vegetables such as carrots, lettuce, potatoes etc.
Horse meat has been banned for use in dog food so in the USA at least you cannot buy dog food that contains horse meat.