Abstract

Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. For a stimulus to be painful, it must be perceived consciously and found to be unpleasant. To describe how pain is transmitted from the site of stimulation to the parts of the brain responsible for conscious awareness, the term nociception is used. A nociceptive stimulus is one which will be felt as painful if and when it reaches the conscious parts of the brain. Nociceptors (pain receptors) are located throughout the body. Some are specific for pain whilst others are sensitive to things (like hot or cold) which may or may not be painful depending on the intensity. Two kinds of pain are transmitted to the central nervous system. The first is pin-prick pain. This is mild, specific to an area and is transmitted rapidly. The second is true pain. This can be severe, is only poorly localised and is transmitted to the central nervous system slowly. Pin-prick pain is the sensory arm of a valuable protective mechanism which alerts the animal to the presence of things which may cause injury. True pain can affect the function and psychological state of the whole animal and is a significant welfare issue if it is severe or prolonged. The first step in dealing with pain in animals is to recognise it. Animals are not able to communicate verbally and so cannot describe their feelings. In order to assess pain, we are forced to make assumptions about how the animal is feeling from its behaviour or physical responses. For example, if a cow is lame, it may be reluctant to walk, lame on the painful leg when it must walk, and show physiological changes in its nervous and endocrine systems. If the pain is prolonged or severe, the animal may become depressed, lose weight and show reduced productivity. Because the animal cannot say "my leg hurts", people working with animals have a responsibility to look out for signs of pain and to investigate their underlying cause.

CB, Johnson

Proceedings of the New Zealand Society of Animal Production, Volume 62, Palmerston North, 348-350, 2002