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The Science Of Measuring Pain

Observing changes in animal behaviour has long been used by producers and veterinarians when assessing animal health. However, using animal behaviour to actually measure pain is a relatively new science because researchers have first had to develop techniques to put hard numbers to what has traditionally been considered a subjective analysis.

Objective measurements of physiological changes, such as a rise in blood cortisol level or heart rate for example, are the standard method of measuring pain and stress found in almostallscientifi literature, saysDr. Karen Schwartzkopf-Genswein, beef cattle welfare researcher at Agriculture and Agri-Food Canada s Lethbridge Research Centre and adjunct professor with University of Calgary Veterinary Medicine (UCVM). Now, new technology and methods of assessing both behavioural and physiological indicators of pain are allowing scientists to gain a better understanding of what an animal may be experiencing. The challenge is collecting data in a way that doesn t interfere with the animals normal response to the procedure being assessed.

There is no single best indicator or silver bullet to gauge pain associated with procedures such as castrating and dehorning, she explains. Researchers use both behavioural and physiological indicators together. The outcomes may at times be contradictory for instance, it s not uncommon for the behaviour of the animal to indicate that there was pain and the physiological measures to show no change, or vice-versa.

That s why it is important to distinguish between acute and chronic pain by measuring as many appropriate indicators as possible at points in time relative to when the procedure was performed, Schwartzkopf-Genswein adds.

It is also why each animal is used as its own control for comparison by measuring the behaviour and physiology of each animal before the procedure to establish what is normal for each one, then assessing changes after the procedure. They can also compare groups of treated animals to a non-treated control group.

For example, following castration they typically see an increase in values for physiological indicators as well as behaviours such as tail flicking and vocalizing, while other behavioural signs, such as lying down or feeding, may decrease.

Producers often question how researchers know they are measuring pain and not the stress of actually taking the samples or temperament. Most of the techniques we use are what we

call non-invasive, meaning they would not cause any more stress than normal handling. We also use anesthesia or analgesia as part of our experimental treatments so we can see if the typical behaviour and physiological responses are eliminated or reduced after administration. If anesthesia or analgesia reduces or eliminates the response, then we can assume the responses were most likely due to pain.

How they do it

Behavioural indicators of pain are routinely used in combination with measuring stress hormones (cortisol, epinehprin and norepinehrin), heart rate, body temperature and inflammation using infrared thermography, along with evaluating production factors, such as gain, feed intake and feed efficiency.

Some of the techniques that researchers have developed for using animal behaviour to measure pain in a research setting include:

1. Observing the frequency of a behaviour associated with pain tail flicks, stomps, kicks at the belly, vocalization, time spent lying down or standing or the number of times the animal change from one behaviour to another with each carrying an equal weight when assessing a procedure. The data is usually captured by trained observers on site or via video for review and documentation at a later time.

2. Detailing changes in eating behaviour with the use of an electronic feed bunk monitoring system that collects data on each individual animal 24 hours a day to monitor feed intake, time spent eating and the number of visits to the feed bunk.

3. Instrumented headgates with strain gauges and accelerometers measure the force and frequency with which an animal hits the headgate while restrained during a procedure. An animal s escape response can be indicative of the severity of pain it may be feeling.

4. Assessing the stride length and gait of intact animals versus castrated animals immediately after the procedure when they exit the chute can indicate whether the procedure is painful. Typically, animals castrated with a knife have a reduced stride length in their back and front legs.

Why do it

A requirement to provide pain medication when performing routine on-farm procedures, such as castrating and dehorning older calves, may become the world standard sometime in the not-too-distant future as the OIE (World Organization for Animal Health) continues its work on animal welfare. It then becomes a sustain-ability issue in that if we want to trade with countries that adopt OIE recommendations, we will have to be up to snuff, says Schwartzkopf-Genswein. At the same time, we have to be aware that we can t simply adopt practices from other countries with completely different management systems and expect them to be effective on Canadian farms and ranches.

Pain mitigation strategies must be appropriate, effective, user-friendly, economical and sustainable for industry. To achieve that goal, researchers must first determine whether a particular procedure is painful, the extent of the pain, and when the pain occurs.

It s best for us as an industry to be engaged, compile the research, and position where the lines should be drawn, she adds. Science can prove where we are doing just fine and don t need to make changes, or it can show where and why changes are needed and the most appropriate way to achieve specific goals.

Schwartzkopf-Genswein uses recent research on the castration of older bulls as an example. Producers have always been encouraged to castrate and dehorn early in the calf s life because people intrinsically believe that it would be least painful at a very young age because the nerves are less developed and there is not as much tissue. However, Alberta feedlots estimate that upwards of 30 per cent of the male calves they receive are still intact. Feedlot managers have indicated that they prefer using the banding method over the surgical method because it is safer, cleaner and easier to do in a feedlot setting.

A 2010 study led by Schwartzkopf- Genswein in collaboration with the UVCM and the Western College of Veterinary Medicine examined the outcome of using pain medication when castrating 210-day-old bull calves by banding compared to a group of month-old bulls castrated without pain medication.

As expected, there was a significant difference in behaviour during the first 30 minutes following application of the band, with far less stomping and tail switching observed and recorded among the group that received a local anesthetic. What they didn t expect was to see a drop in feed intake among the castrated bulls about three weeks out when the testicular tissue sloughed off. Some swelling, indicating inflammation and pain, is oftentimes observed above where the band has been placed.

So, while it may be possible to give pain medication at the time of banding, is it really warranted if the effect is so short-lived? Would three weeks after castration be a more appropriate time? If so, how many days and at what level should treatment be given to control pain, yet allow the animal to continue to function in its environment? What are the best types of pain medications approved for use in Canada that can be easily delivered by producers? Would putting animals through the chute a number of times to administer pain medication create more stress than the stress of coping with the pain itself? Would administering pain medication through feed or water to an entire pen be an alternative? And, what is the effect of the pain medication itself on production?

These are but a few of the questions Schwartzkopf-Genswein and her team hope to address with continuing research on this topic.


Strain gauges monitor movement.


The OIE first identified animal welfare as a priority in its 2001-2005 strategic plan, with the Animal Welfare Working Group formalized in May of 2002 and the first global conference on animal welfare held in 2004. Since May, 2005, the Animal Welfare Working Group has recommended seven animal welfare standards that have been adopted into the Terrestrial Code. They relate to transportation, slaughter for food, killing for disease control, control of stray dog populations and use of animals in research and education.

During 2009-2010, two ad hoc groups on animal welfare and livestock production were formed one for beef cattle and one for broiler chickens with plans underway to establish an ad hoc group for dairy cattle. As of yet, no standards have been approved for any of these production areas.

Standards must be approved by the OIE s 178 member countries before they can be written into the code. Considering the diversity of production systems, climate, genetics and many other variables, it will take time for all these countries to find agreement.

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