This week's blog post is written by Dr. Kurt Vogel, Ph.D, an Assistant Professor Animal Science, Livestock Welfare and Behavior at the University of Wisconsin–River Falls. Dr. Vogel studied at Colorado State University under noted animal welfare activist Temple Grandin. He teaches courses in animal welfare and physiology, conducts research on the impact of management on livestock welfare, recently hosted a series of seminars on societal ethics and animal agriculture, and was profiled in the August issue of Drovers Cattle Network.
By Guest Blogger: Kurt D. Vogel, Ph.D., Assistant Professor of Livestock Welfare and Behavior, University of Wisconsin-River Falls.
In any science-based discussion of painful procedures that are performed in livestock management systems, common terms and phrases like cortisol, epinephrine, heart rate, and vocalization are likely to come up. From the sidelines, it may appear that assessing animal pain is reasonably straightforward: just pull a blood sample, analyze the concentration of a pain-indicating substance in the blood, and – voila! – the amount of pain the animal experienced is revealed. Unfortunately, assessing animal pain is not that simple. There are many factors that influence the quality and suitability of the pain assessment measures that we use. Let’s take a look at a couple of the factors that must be considered when an assessment of animal pain is performed.
The first consideration to make when performing an assessment of animal pain is the suitability of the measurement. Let’s use the stress hormone cortisol as an example. Cortisol is released by the adrenal glands in response to some sort of immediate stressor – fear and pain are a couple of examples. The major physiological role of cortisol is to increase the amount of glucose that is circulating in the blood. The resulting increase in blood glucose gives the body the extra energy it needs to overcome the stressor. This is a small part of the body’s response to an immediate or acute stressor. So, in cases where we need to determine how much stress an animal experiences in response to a short-term painful event, cortisol is quite useful. However, when the animal is under chronic stress, blood cortisol levels will increase immediately after the stress has begun, but will return to normal or near normal even though the animal may still be experiencing some level of pain. This is one of the reasons why cortisol is not, and should not be, the sole indicator of animal pain and stress in scientific literature. From the standpoint of an animal welfare scientist, acute pain and stress is much simpler to assess than chronic stress.
Another challenge to assessing animal pain and stress is accounting for the presence of humans in close proximity to the animals. For most domestic livestock, close contact with a human can be highly stressful. If we plan to assess the amount of pain that calves experience during the application of caustic paste to the horn buds, we have to compare the response of the calves to calves that did not receive the paste application. We call this a ‘sham’ procedure. During a sham procedure, all of the handling associated with the procedure is performed and the same indicators of pain and stress are measured. The data that is collected from the ‘sham’ procedure is then used to factor out the amount of stress that the calf experienced from close contact and handling by humans.
Ultimately, the scientific assessment of the amount of pain and stress that an animal experiences during a painful procedure can be challenging to quantify. Much of the research that has been conducted on the amount of pain experienced by domestic livestock has focused on the amount of acute pain that the animals experienced. Newer studies have identified methods to perform longer-term assessments of pain and stress, but there is still much work to be done to fully understand the chronic pain response in animals.