Global meat consumption to double by 2020

Yet in Europe and North America there is growing concern about the ethics of the way meat and eggs are produced. The consumption of veal has fallen sharply since it became widely known that, to produce so-called "white" - actually pale pink - veal, newborn calves are separated from their mothers, deliberately made anaemic, denied roughage and kept in stalls so narrow that they cannot walk In Europe mad cow disease shocked many people, not only because it shattered beef's image as a safe and healthy food, but also because they learned that the disease was caused by feeding cattle the brains and nerve tissue of sheep.

People who naively believed that cows ate grass discovered that beef cattle may be fed anything from corn to fish meal, chicken litter (complete with chicken droppings) and slaughterhouse waste. Concern about how we treat farm animals is far from being limited to the small percentage of people who are vegetarians or even vegans - eating no animal products at all. Despite strong ethical arguments for vegetarianism, it is not yet a mainstream position. More common is the view that we are justified in eating meat, as long as the animals have a decent life before they are killed.

The problem, as Jim Mason and I describe in our recent book, is that industrial agriculture denies animals even a minimally decent life. Tens of billions of chickens produced today never go outdoors.

They are bred to have voracious appetites and gain weight as fast as possible, then reared in sheds that can hold more than 20,000 birds. The level of ammonia in the air from their accumulated droppings stings the eyes and hurts the lungs.

Slaughtered at only 45 days old, their immature bones can hardly bear the weight of their bodies. Some collapse and, unable to reach food or water, soon die, their fate irrelevant to the economics of the enterprise as a whole.

Conditions are, if anything, even worse for laying hens crammed into wire cages so small that even if there were just one per cage she would be unable to stretch her wings. But there are usually at least four hens per cage, and often more. Under such crowded conditions, the more dominant, aggressive birds are likely to peck to death the weaker hens in the cage.

To prevent this, producers sear off all birds' beaks with a hot blade. A hen's beak is full of nerve tissue - it is, after all, her principal means of relating to her environment - but no anaesthetic or analgesic is used to relieve the pain.

Pigs may be the most intelligent and sensitive of the animals that we commonly eat. When foraging in a rural village they can exercise that intelligence and explore their varied environment. Before they give birth, sows use straw or leaves and twigs to build a comfortable, safe nest in which to nurse their litter.

But in today's factory farms pregnant sows are kept in crates so narrow that they cannot turn around, or even walk more than a step forward or backward.

They lie on bare concrete without straw or any other form of bedding. The piglets are taken from the sow as soon as possible, so that she can be made pregnant again, but they never leave the shed until they are taken to slaughter.

Defenders of these production methods argue that they are a regrettable but necessary response to a growing population's demand for food. On the contrary, when we confine animals in factory farms we have to grow food for them.

The animals burn up most of that food's energy just to breathe and keep their bodies warm, so we end up with a small fraction - usually no more than one-third and sometimes as little as one-tenth - of the food value that we feed them. By contrast, cows grazing on pasture eat food that we cannot digest, which means that they add to the amount of food available to us.

It is tragic that countries such as China and India, as they become more prosperous, are copying western methods and putting animals in huge industrial farms. If this continues, the result will be animal suffering on an even greater scale than now exists in the west, as well as more environmental damage and a rise in heart disease and cancers of the digestive system. It will also be grossly inefficient. As consumers, we have the power - and the moral obligation - to refuse to support farming methods that are cruel to animals and bad for us.

(Peter Singer: this writer is professor of bioethics at Princeton University and the author, with Jim Mason, of The Way We Eat: Why Our Food Choices Matter (c)Project Syndicate 2006.)