20/07/2012 12:57 BST | Updated 19/09/2012 06:12 BST

Whether Vegetable or Animal, Farm Produce is Treated Just The Same: the Case for the Vegan Option Continued

On traditional farms - now called 'alternative' or 'organic' - animals range free in the fields. Their dung fertilises the crops which, in turn, feed the animals. A natural cycle with a rhythm that keeps in step with the seasons. Modern 'conventional' farming, on the other hand, is monoculture: a concentration of a single species. Just hens, or pigs or cattle. 74% of the world's poultry, 68% of the world's eggs, 50% of the world's pig meat and 43 % of the world's beef are produced this way. 25,000 chickens to a shed. The world's largest feedlot holds 150,000 cattle. The world's largest dairy 37,000 cows.

This is factory farming - the scale industrial, its inputs imported and chemical; a system that by design is unnatural, its process violent, unjust, cruel, unfeeling. Machines deliver feed and water, monitor light and darkness, heat and cooling. Farm workers do little more than check that machinery is working and remove dead and dying animals.

Feed is unnaturally dense. High in fat from fish oil or palm kernel oil and high in protein from soya and fishmeal (about one quarter of the global fish catch is used for fishmeal to feed farmed animals). Other sources of protein are bloodmeal, bonemeal, feather meal, poultry by-product meal, slaughterhouse waste and even processed poultry litter. Animals fed this unnaturally high fat and high protein diet grow fast. But it is a diet that suits the industry rather than the animals' digestive systems. Lacking fibre animals can be left feeling hungry and cows unable to ruminate (chew the cud) sufficiently. Indigestion and the resulting obesity bring their own welfare and health problems. Diarrhoea, lameness and heart failure are just a few of them.

Chemicals keep animals alive - there is no alternative when they are crammed together in such vast numbers. Antibiotics - routinely added to feed - control outbreaks of disease and infection (70% of antibiotics used in the developed world are fed to farmed animals). Pesticides and insecticides are sprayed to help fight bacteria, viruses, parasites and to ward off blood poisoning, roundworms and tapeworms.

Traditional farms are arranged to suit the animals. Now animals are selectively bred to suit intensive production. They must grow large as quickly as possible and be as productive as possible. Chickens for meat - bred to have insatiable appetites - put on 50 grams a day and can reach their slaughter weight in 49 days from hatching. Farmed Atlantic salmon now grow to 60 centimetres and three kilos in two years. In contrast a 2 year-old wild salmon would measure about 10 centimetres). Sows have litters of up to 15 piglets even though they have only 12 teats. Ewes now often give birth to triplets even though they only have two teats. Hens lay up to 300 eggs a year - 30 is a natural number. Double-muscled cattle and sheep carry a mutation where muscle growth - the meat - continues uncontrolled. Hugely heavy, but with bone structure no stronger than normal animals, their weight causes sore feet, weak joints, infirmity and pain. Scientists are hoping to pass the double-muscle gene on to pigs and chickens.

In this way animals are treated like vegetables - as if they were inanimate agricultural products. The agri-trade even refers to them as crops: the chicken crop, the lamb crop, the fish crop, the hog crop. Sprayed with insecticides; fed unnatural, alien feed stuffs; and bred to maximise profit, they have been turned into grotesque parodies of their natural selves. (And as a result never before have meat, eggs and milk been so plentiful nor so cheap).

Yet for all the physical changes, science shows that all these animals have needs that are no different from their wild ancestors. Like all animals - including humans - they need the space to carry out their normal behaviour. A place where they can feel safe. And a diet that suits their digestive systems. But when animal production is on an industrial scale it is incompatible with welfare of any meaningful kind.

After several million years of human evolution you might think we could come up with a way of feeding ourselves which doesn't involve such raw cruelty?

Sue Cross is author of On the Menu: Animal Welfare (Published by Pen Press, 2009) and Todays Freaks: An A to Z of How Farm Animals Live and Die. ebook published 2011 and free in PDF form from:

Both books are available from Amazon in the UK and also the US