Does a male piglet experience pain when the testicles are removed during the castration process? And would any pain be reduced by the provision of, for example, a local anaesthetic?

The Danish Animal Welfare Council asked scientists at the Faculty of Agricultural Sciences at the University of Aarhus to find answers to these questions based on available scientific knowledge. The results have recently been published in a Danish report.

Castration is painful for the pig even when it is only a few days old.
(Photo: Janne Hansen)

• It does hurt, confirms senior scientist Mette S. Herskin from the Department of Animal Health, Welfare and Nutrition at the Faculty of Agricultural Sciences. She studies behaviour in animals in pain and has recently started working on a project involving tail docking of pigs.
  
  It is possible, but very difficult to say anything specific about how much, for how long and where the pain is felt.
  
• You cannot simply ask an animal if it hurts, and there is no single pain indicator – a “golden standard“ – neither in their behaviour nor physiologically that can be used as a direct and unequivocal measure of how much pain an animal is experiencing, she explains.

No easy pain indicator

There are substances in the blood that can assist as indicators, but there is no real “pain hormone“. Besides that, pain and stress are very closely connected. It is the same areas in the brain that is activated and many pain reactions are the same as stress reactions. The pain experienced also depends on where in the body the pain is situated and the duration of the pain.

One way to differentiate between pain and stress arising from castration is by carrying out controlled studies. You can remove the pain by, for example, the provision of an anaesthetic. You can also catch and fixate the pig, just like for a real castration, but not actually castrate it. In both cases it is possible to separate pain responses and stress reactions.

• There are rather few studies of pain in pigs despite the fact that they are frequently used in experiments and for pork production. It is mostly pets, horses and laboratory animals (as models for humans) that have been studied and you cannot necessarily transfer results from one animal species to another, says Mette Herskin.

Different kinds of pain

A very obvious reaction to castration is the pig’s squeal. Analyses of the frequencies of the squeal show that the squeal differs depending on whether the pig’ skin is being cut during surgery, the spermatic cords are being pulled, or they are being severed.

• It can hurt the pig when the spermatic cords travelling to the testes are pulled, even if the pig is locally anaesthetized in the testicles, because the cords are attached further up in the abdominal region. It also hurts to be injected in the testicles in order to be anaesthetized and the anaesthetic does not have a full effect in all pigs, explains Mette Herskin.

Post-operative pain is also an issue. Even though there are only a few studies of pain in the period after castration, there are indications that the behaviour of the pigs is affected up to five days following the operation.

Effect of age

It was previously thought that it was best to castrate pigs at a young age, one of the reasons being that healing is faster. There are, however, no indications that newborn animals experience less pain. On the contrary, some experts are of the opinion that babies have an increased risk of heightened pain sensitivity following an operation due to changes in and damages to the nerve system.