Infrared Stress Testing

June 2009

Stock stress levels are measured using infrared thermography at AgResearch

It is quicker and much less invasive than taking blood samples for measuring cortisol. Along with cardiac response it can be used for assessing the “humaneness” of routine on-farm procedures such as castration and disbudding of calves, and to test the efficacy of analgesics.

Animal welfare is also a marketing issue, and it is important that analgesics be used when painful procedures are carried out. This new IR technique indicates that a combination of local (short term) and anti-inflammatory (longer-term) analgesics is better for controlling pain than local alone.

Dr Mairi Stewart, who carried out this research for her PhD, won a KuDOs Emerging Scientist award in last year’s Hamilton Science Excellence Awards.

Increasing consumer concern that food animals are treated humanely has led to more emphasis being placed on “welfare friendly” on-farm practices. Assessing the humaneness or otherwise of such practices is difficult because the techniques normally used to assess pain are themselves invasive and may cause stress responses.

Mairi Stewart carried out research for her PhD into developing a non-invasive method of assessing pain response in cattle – eye temperature combined with heart rate variability (HRV). Eye temperature was measured using infra-red thermography (IRT), a technique being worked on by Canadian researchers.

“They had been using the infrared camera to look at velveting in elk and reindeer but they didn’t really understand why they were getting those results. We wondered whether we could use it to indicate pain and distress in cows,” says Mairi.

“I took it on as a Ph.D. project because I was interested in pain detection, and I also looked at the underlying mechanisms that were driving the responses – we get this change in eye temperature so what does it mean physiologically?”

It was the first time anyone had used IRT in cattle, and Mairi was able to show that when cattle were frightened, stressed or in pain, she could detect changes in the heat from superficial capillaries around the eyes. The changes were caused by differences in blood flow to the eyes as part of the response of the animal to the pain, and there were different responses to different painful events.

Mairi found that with disbudding (cauterisation of the horn buds), the superficial pain caused a drop in eye temperature as the sympathetic nervous system diverted blood away from the extremities to vital organs. In contrast, with castration the deep tissue pain caused an increase in eye temperature as the parasympathetic nervous system acted to reduce blood pressure by dilating blood vessels.

Local anaesthetics reduced the pain response considerably after disbudding but only a little after castration, showing that other analgesics are necessary.

The IRT/HRV technique shows promise as relatively easy and quick research tool for assessing the painfulness of procedures on animals and the effectiveness of analgesics. It will help researchers to help farmers by developing more acceptable methods of carrying out routine farming operations and thus help maintain market access.

There are also other potential applications for this technology on farms, says Mairi.

“The Canadian group has been developing techniques to assess eye temperatures in feedlots in conjunction with EID, so when a calf comes up to a trough its head breaks a beam and an IR camera takes a shot of the eye. They have found that changes in eye temperature have been correlated with early signs of diarrhoea. They have also used IR cameras mounted high in abattoirs to detect animals that are too hot and stressed to be slaughtered, and thus reduce the incidence of dark-cutting meat.”

“In New Zealand we could use IRT for detecting heat and cold stress and any kind of inflammation. Vets have used it to look at lameness, and there has been some work on using IRT to detect inflamed udders. Perhaps it could be used in robotic milking systems where shots of the eyes or udder could provide early detection of animals that are unwell.”

Mairi’s conclusions about disbudding and castration:

• Local anaesthetics should be used wherever possible, and a combination of both anaesthetics and non-steroidal anti-inflammatories is best to relieve pain for longer.

• We need to find more farmer-friendly ways of administering these analgesics. There are technicians who do a lot of the dehorning and disbudding, so we just need to train those people up on how to use these drugs, but also just developing more novel and practical ways for farmers to administer analgesics to calves.

• Supermarkets are developing welfare standards and labelling systems. Farmers who comply will have better options when it comes to selling their products.