Whip strike reverberating on the flank of racehorse Juan Carlos. Do whips hurt horses?

Science answers: Do whips hurt horses?

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The racing industry insist that padded whips don’t hurt horses. But two humans who volunteered to be struck by a padded whip on camera said it hurts bad – so, is there any anatomical reason to believe that horses don’t feel pain in the same way we do? As part of an ABC Catalyst investigation into horse whipping, a forensic veterinary pathologist, Dr Lydia Tong, helped get to the bottom of the question and reported her findings.

Large animals like horses are commonly said to have ‘thick skin’ – and thick skin is associated with stoicism and insensitivity. But is this assumption fair on horses? Has anyone actually ever looked at this scientifically?

Whilst there is some information out there about horse skin thickness it appears that, as far as we can tell, no one has ever looked specifically at the pain sensing fibres in the skin of horses.

We decided to see if horse skin thickness and nerves were really that different to human. To do this, I took a piece of horse skin from the flank area (the area where the horse is usually whipped), as well as a piece of skin from the equivalent area on a human. Using both routine and special techniques, I was able to look at both the structure of the skin, but also the precise location and amounts of nerve tissue.

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No one has ever used this technique in horse skin before, nor have they specifically compared human skin to horse skin in this way.

I looked at the skin to answer two questions–

  1. What was the difference in the thickness of horse and human skin?
  2. How many nerves does the horse have in its skin in comparison to humans.

Examination of the horse and human skin under the microscope revealed a few surprising things:

  1. The horse skin was thicker, but by less than 1mm! And this was primarily just the deep collagen tissue (which sits below the superficial pain sensing fibres).
  2. The horse epidermis (the very top most layer of skin where the pain sensing nerves are found) was actually thinner than the human epidermis. This means that the horse has fewer skin cells lying between the source of the pain (e.g. a whip), and its sensitive nerve endings. 
  3. Finally – a special stain that only stains nerve tissue revealed that the horse appears to have considerably more nerve endings in its skin than the human skin, including the nerves in the epidermis (superficial cells) where the pain sensation primarily occurs.

In some ways you could therefore argue that when it comes to pain, the horse’s skin is thinner.

There are more nerve endings in the horse skin than the human skin, including in the epidermis (the layer on top with all the blue circles). These represent sensory fibres, including those which feel pain. We were astounded by these simple findings.

This small pilot study suggests that horse skin really doesn’t have all the supposed ‘padding’ from pain that we often assume larger animals have. And even more revealing than that, the skin of the body – where we whip horses – may have even more sensation than ours.

To really get to the bottom of exactly how human and horse skin differs in thickness and sensation, we need to look at skin from more people and horses. For that reason, I will be extending this work to a full sized research project. I believe that the best way to make a decision about horse whipping is by establishing the facts through science. Are we using pain to make horses run faster?

So far, it certainly looks like it.

Figure 1. A piece of horse and human skin side by side, showing a comparison of depth. The pink area shows the collagen (dermis), and the thin purple area at the top is the epidermis, where most of the painsensing nerve fibres are found.
Figure 1. A piece of horse and human skin side by side, showing a comparison of depth. The pink area shows the collagen (dermis), and the thin purple area at the top is the epidermis, where most of the painsensing nerve fibres are found.
Figure 2. A close up of the very top layer of the skin (epidermis) where the sensitive pain sensing nerve fibres end. The human epidermis is thicker than the horse epidermis, so there are more cells lying on top of the nerve endings.
Figure 2. A close up of the very top layer of the skin (epidermis) where the sensitive pain sensing nerve fibres end. The human epidermis is thicker than the horse epidermis, so there are more cells lying on top of the nerve endings.
Figure 3. A special staining technique called “immunohistochemistry” allows us to specifically stain up only nerve endings, in this case they have been stained a bold red.
Figure 3. A special staining technique called “immunohistochemistry” allows us to specifically stain up only nerve endings, in this case they have been stained a bold red.

Read the transcript of the Catalyst story here.

Dr Lydia Tong is a veterinary pathologist who investigated the thickness and sensitivity of horse skin
Dr Lydia Tong

Lydia is Taronga Zoo's zoo and wildlife pathologist and is responsible for conducting diagnostic surgical pathology and necropsy of any and all animals in Taronga's care. Lydia trained in veterinary medicine at the University of Cambridge and did her post-graduate training in pathology at the University of Sydney. She has a diverse professional background as a clinical vet and pathologist, working with domestic and wild species around the world, including Borneo, Micronesia, Papua New Guinea, South Africa, East Timor, Vanuatu, Tonga, the UK and Australia.

In her role as Taronga's in-house pathologist Lydia works with a broad range of exotic and native species including wild and captive mammals, birds, reptiles, amphibians, fish, and invertebrates. As part of her role she also provides consulting services for other zoological collections, wildlife sanctuaries, and animal welfare organisations. Lydia has specialist expertise in forensic pathology of animals and regularly performs forensic necropsies of animals or animal remains suspected to be victims of, or otherwise involved in, criminal acts. She managed the first excavation and forensic analysis of a mass grave of any species on Australian soil and has assisted the NSW Coroners office with homicide investigations involving animals. She has been deployed overseas by Taronga to conduct field necropsies on critically endangered megafauna.

She is passionate about pathological and forensic research that leads to positive welfare outcomes. Currently she is part of a Taronga-led team working to develop forensic scientific methods to combat the illegal wildlife trade. Other areas of research include osteopathology and zooarchaeology, pathology of the short-beaked echidna, the pathology and diagnosis of animal abuse, veterinary medical entomology, avian tuberculosis, and the links between animal cruelty and interpersonal violence.

She is currently Secretary of the Australian Society of Veterinary Pathology, and in 2016 she was the inaugural winner of the RSPCA Australia Hugh Wirth Future Leader in Animal Welfare award.

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