Editor's note: First in two-part series on measuring pain in cattle.
Pain can be a difficult thing to quantify. In humans, it's common to use the Universal Pain Assessment Tool which is a 1–10 scale patients can use to verbalize their pain level. In non-communicative patients, the Wong-Baker facial grimace scale also helps caregivers assess pain on the same 1–10 scale (see sidebar).
But how do you ask a bovine what pain level it is experiencing? Like other prey animals, cattle are adept at hiding a certain level of pain. Some of the current subjective methods for identifying pain in cattle in include looking at changes in milk production, growth (meat production), abnormal activity, attitude, appetite, heart rate, respiratory rate, rectal temperature, defecation, urination and self-care (e.g. cleaning of nose, switching tail, ear flicking).
Measuring pain can be even more difficult. David Anderson, DVM, MS, Dipl. ACVS, Kansas State University, says some of the methods used to measure pain include heart rate, respiratory rate, rectal temperature, serum cortisol, walking distance and lying time.
Kansas State's Hans Coetzee, BVSc, Cert CHP, PhD, Dipl. ACVCP, adds to this list behavioral assessment/scoring, growth and performance, and changes in thermal threshold after morphine administration as ways to measure pain in cattle.
But, these methods aren't perfect. "The struggle with these traditional methods is that they are not specific to pain, have limited accuracy, are highly variable based on management and environmental factors, and are inconsistent," explains Anderson. Anderson is completing a research study looking at the traditional physiological stress indicators (heart rate, respiratory rate, rectal temperature, rumination, attitude, defecation) as measures of comfort after surgery. "In this study, we found that none of these factors were significantly different after surgery, as compared to pre-operative baseline. Also, none of these factors were useful in predicting post-operative complications such as incision infection, toxemia, death, etc."
One of the challenges associated with using behavioral scoring systems is repeatability between assessors. Current FDA regulations require studies to be repeated at different trial locations. "It is not practical to have the same assessors do the scoring at all these trial sites," Coetzee notes. "It is therefore difficult to establish consistency in scoring systems. Furthermore, most people can tell if an animal is non-weight bearing on one limb, but more subtle changes in gait are much harder to assess using a visual scale.
There are numerous scoring systems out there but getting consistency in applying these systems is very difficult, Coetzee adds. "The goal with developing science-based tools is to move away from relying on subjective scoring systems. If physiological, neuroendocrine or behavioral changes can be measured as opposed to visually scored it is likely to be much more repeatable. It is also more likely that these measures will be modulated following analgesic drug administration." And this, he says, is a prerequisite for designing effective analgesic drug regimens.
Cattle are instinctually stoic. They respond to adverse stimuli by decreasing interactive activities (more lying time, less movement). "This is very different from species such as horses where pain causes increased anxiety and stimulation to stay standing and ready to run," Anderson says. "Interestingly, veterinarians commonly accept that there are striking differences among breeds of cattle such as Holstein vs. Brahman, but little to no research has focused on this apparent psychological effect."
Lameness in pain studies
Many of the bovine pain models the Kansas State University group is using revolve around lameness. Lameness is a good example of "pain" in cattle that is ethically and morally important to treat. With the common bovine surgeries (castration, dehorning, C-section, displaced abomasum) the stimulus is known, the conditions for the stimulus can be controlled, and pain can be prevented when desired, Anderson explains. The pain stimulus is discrete and of relatively short duration. In contrast, lameness occurs spontaneously and causes chronic, persistent pain which causes rapid weight loss, dramatic decrease in milk production and marked loss of growth.
"This type of pain is debilitating to the animal and causes significant loss in productivity," Anderson says. "Society is increasingly intolerant of failure to address animal pain and discomfort. Lameness is one of the most common causes of pain in cattle and failure to address lameness will likely erode consumer confidence in animal agriculture's ability to safeguard the health and well-being of livestock."
"The induced lameness model we are in the process of developing will increase our understanding of the physiological, behavioral and neuroendocrine effects of lameness in cattle," explains Coetzee. "This model is also important in terms of our understanding of how analgesic drugs mitigate pain associated with lameness. Also, having an induced model provides us with a way of collecting ‘before and after" data which is important for model validation."
To study the "before and after" effects of pain and lameness on cattle, amphotericin B was injected into the lateral distal interphalangeal joint. This product produces a mild to moderate but transient synovitis arthritis. Changes in the animals" pain level and gait were quantified using pressure mats and accelerometers.
Accelerometers are devices that can be used to measure posture (standing vs. lying) and activity (static or dynamic such as walking) in cattle. The remote, non-invasive devices record information providing insight about cattle behavior throughout the day without the need for human observation. "The advantages of this system include the ability to continuously monitor the animals, and provide objective measures of behavior differences," explains Brad White, DVM, MS, also of Kansas State University. "Previous research has documented that following castration, cattle spent more time standing in a 24-hour period, but most of the increased time standing occurred in the middle of the night, a time when animals would typically not be observed. This technology offers an opportunity to objectively measure behavior changes."
Three-dimensional accelerometric analysis of an induced arthritis of the distal interphalangeal joint of feedlot calves allows for objective, non-invasive analysis of arthritis lameness. Analysis of accelerometer data revealed statistically significant differences in activity in feedlot calves with transient arthritis, including increased time lying down and increased time walking when not recumbent. "Further breakdown of the data revealed that marked differences in activity were associated with time of day," White says. "Most activity occurred during daylight hours." Thermography results revealed the model produced a mild degree of inflammation, Anderson notes.
More succinctly, White says, is that "the accelerometers provided an objective measure of the increased amount of time cattle spent lying after arthritis induction, and one advantage of this method was that we were able to identify differences by time of day without potential behavioral influence due to constant human observation."
The pressure mat is a way of measuring the amount of pressure that the animal puts through the foot when it contacts the ground. Also, the pressure mat can "map" the distribution and direction of the pressure throughout the weight-bearing phase of stride. "By doing this, we can detect changes in the comfort in a limb as a sensitive way of detecting lameness," Anderson says. "How much pressure is applied, what surface area of contact is used, what direction the pressure is applied, the stride length of the limb, and for how long the foot contacts the ground can provide important data regarding the usage of a limb from moment to moment. Thus, the pressure mat can be used to measure sudden or gradual changes over time."
Anderson says the pressure mat is an excellent way of quantifying changes in limb use and measuring the effect of treatment. "We can determine lameness, measure its severity, and measure responses to treatment or changes in management designed to lessen lameness."
Thermography is another tool being used to study pain. Thermography is a way of detecting surface temperature of skin, eyes, etc. Blood flow in the skin changes with sympathetic tone. Sympathetic tone increases with fear, anxiety, pain, etc. "We are studying the usefulness of high definition thermography to detect pain or discomfort in cattle," Anderson says. "We are looking at the ability to continuously and instantaneously detect rapid changes in pain threshold by using high-definition thermography to detect changes in blood flow."
Chute exit speeds
Some tools that sound like a good idea don't always perform to the level needed because of individual cattle variation. There are several studies that have been conducted the United States and in Australia that have used radar speed cameras or barrel-racing timing devices to measure the speed of cattle exiting a squeeze chute. "It has been demonstrated that cattle with faster exit speeds have lower weight gains, more sickness and more dark cutting meat," Coetzee notes. "However, in our experience, this measurement is strongly influenced by individual animal temperament and may not be specific to pain. In fact, we have not observed statistically significant differences in exit speed in quiet Holstein cattle before and after dehorning and castration." This suggests, Coetzee says, that there may be significant breed differences that may limit the utility of chute exit speed measurement as a science-based tool for pain assessment.
Heart rate and pain
Heart rate is another tool that has been used to study pain. "Although we have observed marked increases in heart rate associated with castration and dehorning, we have not had an opportunity to analyze the data from recent studies to provide a definitive answer to the question of correlating heart rate and pain," Coetzee says. One concern with traditional heart rate assessment through auscultation is that this required frequent handing of the animals that could confound the results. "We believe that the use of a telemetric heart rate monitoring system that we are validating may be a useful tool to remotely measure changes in heart rate."
Anderson has also used this tool in his research monitoring peri-operative pain, and found that heart rate was not a sensitive indicator of comfort.
Why we need these studies
Currently, the FDA requires that in order for an analgesic drug to have a label claim for pain relief that validated methods of pain assessment are used in the target species. "The complication in food animals is that there are currently no validated methods of pain assessment," Coetzee states. "Therefore, studies to identify and validate robust, science-based pain assessment tools are critical to facilitate analgesic drug approvals for use in food animals."
Coetzee notes that the Kansas State group is also working to validate similar techniques for use in swine. "I am confident that with continued research efforts in this area by a number of different groups that we will be able to validate a system of analgesic drug assessment over the next 3–5 years," Coetzee says.
What you can do right now
Coetzee says it is imperative that veterinarians work with producers to develop protocols to minimize pain and suffering in farm animals. "We can no longer allow cost and convenience from preventing us from fulfilling a moral obligation we have toward the livestock in our care. Equally, we as researchers must continue to identify and validate cost-effective and time efficient protocols to improve animal welfare. This includes training producers to identify early signs of disease in animals and to implement effective therapeutic protocols."
The importance of pre-emptive analgesia should also be emphasized, Coetzee says. "This way we can reduce the impact of central sensitization or so called ‘wind-up" that occurs following a painful procedure."
Cattle handing facilities should also be designed to minimize pain and distress. "Much of what we refer to as ‘common sense" in animal husbandry terms needs to be continuously emphasized and refined to optimize animal well-being," Coetzee summates. "We can't just assume that producers know it simply because they have raised cattle for generations. It is attention to detail that makes all the difference."
Next issue: Castration and pain studies.