Following on from my blog post about the "murder" at the Nanakuli animal shelter, here is an account from Wikipedia of the mass murder process at a slaughterhouse (this is not for the faint of heart):

The slaughterhouse process differs by species and region and may be controlled by civil law as well as religious laws such as Kosher and Halal laws. A typical procedure follows:

Cattle (mostly steers and heifers, some cows, and even fewer bulls) are received by truck or rail from a ranch, farm, or feedlot.

Cattle are herded into holding pens.

Cattle are rendered unconscious by applying an electric shock of 300 volts and 2 amps to the back of the head, effectively stunning the animal,[8] or by use of a captive bolt pistol to the front of the cow's head (a pneumatic or cartridge-fired captive bolt). Swine can be rendered unconscious by CO2/inert gas stunning. (This step is prohibited under strict application of Halal and Kashrut codes.)
Animals are hung upside down by one of their hind legs on the processing line.

The carotid artery and jugular vein are severed with a knife, blood drains, causing death through exsanguination.

The head is removed, as well as front and rear feet. Prior to hide removal, care is taken to cut around the digestive tract to prevent fecal contamination later in the process.

The hide/skin is removed by down pullers, side pullers and fisting off the pelt (sheep and goats). Hides can also be removed by laying the carcass on a cradle and skinning with a knife.

The internal organs are removed and inspected for internal parasites and signs of disease. The viscera are separated for inspection from the heart and lungs, referred to as the "pluck." Livers are separated for inspection, tongues are dropped or removed from the head, and the head is sent down the line on the head hooks or head racks for inspection of the lymph nodes for signs of systemic disease.

The carcass is inspected by a government inspector for safety. (This inspection is performed by the Food Safety Inspection Service in the U.S., and CFIA in Canada.)

Carcasses are subjected to intervention to reduce levels of bacteria. Common interventions are steam, hot water, and organic acids.

Carcasses (typically cattle and sheep only) can be electrically stimulated to improve meat tenderness.

Carcasses are chilled to prevent the growth of microorganisms and to reduce meat deterioration while the meat awaits distribution.
The chilled carcass is broken down into primals and subprimals for boxed meat unless customer specifies for intact sides of meat. Beef and horse carcasses are always split in half and then quartered, pork is split into sides only and goat/veal/mutton and lamb is left whole

The remaining carcass may be further processed to extract any residual traces of meat, usually termed mechanically recovered meat, which may be used for human or animal consumption.

Waste materials such as bone, lard or tallow, are sent to a rendering plant. Also, lard and tallow can be used for the production of biodiesel or heating oil.

The waste water, consisting of blood and fecal matter, generated by the slaughtering process is sent to a waste water treatment plant.
The meat is transported to distribution centers that then distribute to retail markets.