A wider perspective:As far as the UK is concerned the last 30 years has seen a huge increase in legislation concerning food safety and animal welfare. This has mainly been driven by EU legislation. Many years ago I was able to put a couple of pigs in the back of a landrover and drive 5 miles to a local smallholder/butcher who processed much of his own meat.2 Days later I could pick up a couple of boxes of processed meat including virtually everything but the squeak. Today the increased legislation has destroyed all but a few of the old traditional abbatoirs. leading to large factory scale enterprises, created by the additional costs required for compliance. As a result animals travel further to slaughter houses. Not ideal but increased vigilance for food safety comes at the price of probable increased stress for the animals due to vastly increased journey times. (although even this is regulated)

Despite comprehensive legislation, inspections and controls, some abuse does occur, hence the call for cctv surveillance.

https://www.gov.uk/guidance/farm-animal-welfare-during-transportation

https://www.food.gov.uk/sites/default/files/foi-approval-slaughterhouses.pdf
http://news.bbc.co.uk/1/hi/uk/1191286.stm (old but useful history)

http://webarchive.nationalarchives.gov.uk/20150401003646/http://www.food.gov.uk/enforcement/monitoring/meat/reviewofmeatcontrols

https://www.gov.uk/government/collections/welfare-of-animals-at-the-time-of-killing


http://www.oie.int/en/for-the-media/editorials/detail/article/the-role-of-the-veterinarian-at-the-abattoir/

https://www.gov.gg/CHttpHandler.ashx?id=102135&p=0