Processing plants are usually set up to handle 100's of equines in a day. The enter long chutes and slide or are electrically prodded into a Kill box.
The horses are terrified, and often the stun bolt does not work (horses are naturally quicker and more headshy than cattle and the killbolts are...
Please send me the address of the video you watched. I know it is not calm and serene. Horses are flight animals, they smell and sense what will happen...
besides that, the chemicals in horsemeat make it an unhealthy product. Check on the info on website flyingfilly.com