Since at least the 1960s there has been increasing awareness of the effects of intensive farm animal production on animal welfare. One of the events that opened the eyes of a great many people was the publication of the book Animal Machines: The New Factory Farming Industry by Ruth Harrison in 1964. In the book Harrison describes some of the practices of modern animal production, such as keeping laying hens in small cages, the tethering of gestating sows, and keeping bull-calves one-by-one in small crates.
"Life in the factory farm," she wrote, "revolves entirely around profits, and animals are accessed purely for their ability to convert feed into flesh or 'saleable products'." However, even though many people seem to agree with this, the consumption of meat and other animal products is still on the rise, not only in the West but even more dramatically in countries like India and China. Thus, ethical issues concerning the way farm animals are being treated will not go away.
Go to the introductory text 'Breeding and biotechnology in farm animals - ethical issues'
You can find more research publications on farm animal ethics here