Animal pain: What do they feel?

As pet owners, we have a responsibility to care for our animals, but when it comes to animal health, it can often be difficult to determine whether they are feeling pain, how intense this pain is, and whether or not the animal should be taken to the vet. Unlike humans, animals cannot simply tell someone where and how much they are hurting. Instead, we must be on the look out for subtle signs that could indicate a bigger problem. Dealing with and managing animal pain is a part of their ownership and our duty of care and ability to acknowledge future consequences means we must weigh up certain moral dilemmas such as subjecting your dog to a blood test in order to find out if he is suffering from a more serious or painful condition.

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This kitten will be experiencing acute pain from the injection.

When taking my pets to the vet, I often wondered what they were feeling when having injections. Neither of them seemed to even notice when the needle went in, let alone cry out like many humans would. Does this mean they didn’t feel the injection, or did they just put up with the pain? Is the pain of getting an injection the same for animals as it is for humans? This is a very difficult question to answer, for while the majority believe animals can feel pain, it is very hard to relate the pain animals feel to the pain humans feel. Instead of comparing painful events, the best way to recognise suffering is to look for species-specific signs, whether they be physiological or behavioural.

Recognising pain in animals is an extremely important aspect of veterinary work. A vet must examine an animal that is brought in by a worried owner and judge whether it is feeling pain and what the possible causes could be. Post-operations, vet nurses will monitor individuals for signs of pain, often using numerical scoring systems, and the vet will recommend post-operative care based on the individual animal.

Pain can be classified as either acute or chronic, depending on its duration. Acute pain is short-term pain which occurs on injury and during the healing process. For example, the pain from a whip used in horse riding is acute pain, as is the pain you feel after an operation. Chronic pain on the other hand is long-term pain such as that felt by a Labrador suffering from arthritis or laminitis in a horse. If an animal is experiencing chronic pain, a vet may perform surgery to alleviate this long-term pain, but after the operation, the animal will feel acute pain from their stitches.

There are also different types of pain depending on where the pain originates. Pain coming from body tissue, e.g. the skin of muscles, is described as somatic pain, pain from an organ is visceral pain and pain from the nervous system (nerves, brain and spinal cord) is called neuropathic pain. However, for pet owners, the most important things to know about animal pain are how to recognise it and whether it is acute or chronic.

Pain occurs through noxious stimulation and nociception. Sensory cells called nociceptors detect hurtful (noxious) stimuli such as intense heat, and transmit a signal to the brain via the spinal cord. The brain reacts by producing the feeling of pain. During general anaesthetic, nociception still occurs, but the feeling of pain is not produced. Noxious stimulation can also be internal, with nociceptors being stimulated by the chemicals present during the inflammatory response or other non-normal processes. However, the brain cannot distinguish between these signals and those from the skin and muscle, so pain is moved to an external part of the body. This is known as referred pain. For example, pain caused by nociception in the heart is often referred to the inside of the forelimb.

Even in humans, pain can be difficult to measure, with most signs coming directly from the patient. In animals, researchers and veterinarians have developed different assessments to recognise and rate the pain an individual is feeling. Although there are physiological clues, pain assessment in animals is often subjective and based largely on their behaviour, examining their locomotion, overall demeanour, vocalisations and attention to wound. Certain behaviours are then given a rating, and these ratings are added up to give an overall pain score.

For example, the Short Form of the Glasgow Composite Pain Scale asks a series of questions and asks for a rated response.

Look at the dog in the kennel. Is the dog:

  • Quiet                                             0
  • Crying or whimpering             1
  • Groaning                                      2
  • Screaming                                   3

These types of subjective pain assessments have been created for a variety of species, although pain can be harder to detect in prey species such as rabbits due to a lack of vocalisations. Vets and vet nurses use these scales to correctly prescribe pain-relief medicine after surgery.

Just like for humans, there are a number of drugs available for animals that can be given by veterinarians to relieve pain. These include opioids, anti-inflammatory drugs (both steroid and non-steroid) and anaesthetics. These drugs can help reduce an animal’s feeling of pain if they have had an operation, or suffer from a long-term condition such as osteoarthritis.

Feeling pain doesn’t always mean the body isn’t working, and it often has important adaptive explanations. For example, if you place your hand on a hot kettle, you should feel a burning sensation and pain which will make you quickly withdraw. What would happen if you didn’t feel pain? You wouldn’t realise the hot kettle is actually damaging your skin and could end up with some pretty severe burns. This is the same reason animals feel pain. However, it is widely agreed that some pain is not useful, and is in fact maladaptive, causing more harm than benefit.

So, why is it important we recognise pain in animals? Looking beyond general pet ownership and veterinary practises, being able to recognise and score pain is a key part of animal management. By researching animal pain, new guidelines can be put into place to alleviate unnecessary suffering. In farming, for example, practises such as tail docking and castration using rubber rings in lambs are common place, but by recognising and scoring pain, studies have found their pain can be alleviated by administering local anaesthetic to the docking site (Kent and Graham, 1998). Being able to recognise pain behaviour in calves also led to better pain relief post dehorning (Faulkner and Weary, 2000) and cryoanaesthesia significantly reduced the pain felt during ear notching or tagging in piglets (Leslie et al, 2010).

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A lamb with a docked tail.

Recognizing pain also helps you make the decision as to whether a pet should be put to sleep. The decision to euthanize is always a hard one, especially when they don’t always seem to be in pain as is the case with many small animals, but by listening to the vet and understanding the discomfort the animal is in, you can prevent further suffering and deterioration.

During an animal’s life, it will always experience a certain amount of discomfort. The key is that this suffering should be minimized to the greatest degree possible, and that the benefit to the animal of that short-term suffering should outweigh the cost. Take a kitten, for example. When you take him for his vaccinations, he will feel acute pain, but if you didn’t have him vaccinated, he could become ill and would need to go to the vet where he would end up with more injections or blood tests, which could have been easily prevented by giving him the initial injection.

Recognising and assessing pain is important for pet owners, veterinary staff and animal handlers alike. By using simple scoring assessments, we can better understand how our animals are feeling, and what we can do to alleviate this pain. Rather than comparing animal pain to human pain, we should be using these assessments to understand pain on an individual scale and treating it accordingly. As a species capable of rational thought and higher level thinking, we have a responsibility to the animals in our care to make sure their lives have a high standard of welfare. To subject an animal to further illness, pain or mental anxiety, all because we didn’t want them to feel any pain in the first place would be going against this duty of care, and any prospective pet owners or handlers should be aware of this responsibility before taking on a new animal.

Glossary

  • (Animal) pain- A negative sensory experience resulting from nociception. Alerts animal to harm or potential harm and can lead to altered physiology and behaviour.
  • Nociception- The detection and transmission of noxious stimuli to the brain by noiceceptors, resulting in a feeling of pain.
  • Nociceptors- Sensory cells in the body which detect harmful or potentially harmful stimuli.
  • Noxious stimuli- harmful stimuli
  • Referred pain- Pain from internal organs which is transferred to an external body part.

If you believe your animal is in pain, contact your nearest vets. Do not attempt to self diagnose your pet and do not give human pain relief drugs to your animal.

Acknowledgements

  • J.E. Kent, V. Molony, M.J. Graham, Comparison of methods for the reduction of acute painproduced by rubber ring castration or tail docking of week-old lambs, The Veterinary Journal, Volume 155, Issue 1, 1998, Pages 39-51, ISSN 1090-0233, http://dx.doi.org/10.1016/S1090-0233(98)80033-6.
  • P.M. Faulkner, D.M. Weary, Reducing Pain After Dehorning in Dairy Calves, Journal of Dairy Science, Volume 83, Issue 9, 2000, Pages 2037-2041, ISSN 0022-0302, http://dx.doi.org/10.3168/jds.S0022-0302(00)75084-3.
  • E. Leslie, M. Hernandez-Jover, R. Newman, P. Holyoake, Assessment of acute pain experienced by piglets from ear tagging, ear notching and intreperitoneal injectable transponders, Applied Animal Behaviour Science, Volume 127, Issie 2-3, 2010, Pages 86-95, http://dx.doi.org/10.1016/j.applanim.2010.09.006
  • J.E. Kent, V. Maloney, Guidelines for the Recognition and Assessment of Pain in Animals, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Summerhall, Edinburgh EH9 1QH, Sponsered by DEFRA, SEERAD, BVAAWF and UFAW. Last accessed 29/08/16.

 

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