At common law animals were formerly classified as wild by nature (ferae naturae) or tame by nature (mansuetae naturae), referring to the species in general rather than the individual animal. The owner of a wild animal was strictly liable for any damage it caused. The owner of a tame animal was liable for damage it caused if he knew that it had a vicious tendency abnormal in the species (the scienter rule). Special rules applied to damage done by cattle (see cattle trespass) and dogs. The common law classifications have been largely replaced by modern statutes.
For purposes of civil liability in England, animals are classified as belonging to a dangerous or a non‐dangerous species (Animals Act 1971). A dangerous species is one not commonly domesticated in the British Isles, fully grown members of which are likely to cause severe damage. The keeper of an animal of a dangerous species is strictly liable for any damage it causes. Liability for damage done by other animals arises either under the Animals Act, if the animal was known by its keeper to have characteristics not normally found in that species, or only normally found in particular circumstances, which made it likely to cause that kind of damage; or under ordinary rules of tort liability. Thus carelessly allowing a dog to stray on the highway can make the keeper liable in negligence if it causes an accident, and excessive smell from a pig farm can be an actionable nuisance. The 1971 Act also imposes strict liability for damage done by trespassing livestock, which includes cattle, horses, sheep, pigs, goats, and poultry. The keeper of a dog that kills or injures livestock is liable for the damage, except when the livestock was injured while straying on the keeper's land. If livestock is worried by a dog, the owner of the livestock (or the owner of the land on which the livestock lives) may kill or injure the dog to protect the livestock.
Dangerous wild animals may require a licence under the Dangerous Wild Animals Act 1976. Keeping dogs of a species bred for fighting is an offence under the Dangerous Dogs Act 1991. The use of guard dogs is controlled by the Guard Dogs Act 1975. Other statutes protect various species, control importation of animals, and deal with animal diseases. See also animal cruelty; cockfighting.