Pigs are farmed in many countries, though the main consuming countries are in Asia, meaning there is a significant international and even intercontinental trade in live and slaughtered pigs. Despite having the world's largest herd, China is a net importer of pigs, and has been increasing its imports during its economic development. The largest exporters of pigs are the United States, European Union, and Canada. As an example, more than half of Canadian production (22.8 million pigs) in 2008 was exported, going to 143 countries. Older pigs will consume eleven to nineteen litres (three to five gallons) of water per day.Pigs are highly intelligent, inquisitive, adaptable, social animals that learn quickly. In many learning tests they can out-perform dogs! Pigs forage and root for food (a strong natural behaviour) and given the opportunity they eat a wide range of vegetables and animal products, including carrion (dead animals). Pigs mainly use their good senses of smell and hearing to explore their environment relying less on eyesight. Pigs are expressive animals and can produce a wide range of different calls/vocalisations. Their tails can often tell you about their mood - happy pigs often have curly tails whereas pigs that are stressed may tuck their tails between their legs. In cold weather pigs often huddle to keep warm, whilst in warm weather they wallow in water and mud to keep cool where possible. Pigs are sensitive to extremes of climate as they have no sweat glands (except for on the tip of their snout) and no thick hair cover, relying on fat for insulation. Pigs prefer to live in stable families or small groups. They can be aggressive to each other if unfamiliar animals are mixed. Boars are often solitary. Pigs are clean animals; if provided with appropriate housing they will use one particular area for dunging, keeping their lying/sleeping area clean. Shortly before giving birth sows develop a strong desire to build a nest from materials such a
