Measuring and managing stress levels in captive animals can be useful in maintaining its wellbeing and is usually monitored by measuring hormone levels and monitoring behaviour. It is also possible to see a difference in core body temperature.

 

 

When reacting to a stressful event, vasoconstriction occurs in the extremities of the body, meaning the surface skin temperature in certain areas will decrease for a period of time.

Dr Katherine Herborn of Newcastle University looked at whether the magnitude of skin cooling can be used to monitor stress in chickens. This included seeing whether the change in temperature in the wattle and comb correlated with the amount of and type of stress put on an individual.

 

comb-and-wattle
The wattle and comb can vary in shape and size in chickens. this portrays one of the weaknesses of thermal imaging, in that some individuals it will be harder to detect change. Image from Adelaide Chicken Sitting Service.

 

 

To look at acute stress, levels of the stressfulness of two different handling techniques using behavioural and hormonal markers were established. Thermal imaging was then taken before, during and after being handled in one position or another.

 

 

handling-positions
Figure from HerbornĀ et al., 2015, showing the handling positions used in the experiments, as well as the results gathered.

 

The imaging correlated with the expected stress levels experience in each position. In the more stressful position, there was a greater decrease in surface skin temperature before returning to baseline temperature. Unexpectedly, a short period of time after the stressful event the skin temperature exceeded the baseline temperature in the side-pinned hens.

This is thought to be due to a higher core temperature being present in the more stressful condition, therefore when vasoconstriction stops there is more heat to dissipate.

In humans and rats it has been shown that there is a core temperature increase with chronic stress, however, skin temperature is more difficult to predict due to general thermoregulatory processes. In farm chicks there is less need for these processes as their environment is carefully controlled, therefore there is a chance to look at links between skin temperature and chronic stress.

 

 

In a playback trial, three separate flocks were played either a control, anxious or distressed chick call every 15 minutes for 24 hours. Thermal imaging showed no difference in the control chicks after one (acute stress) or seven (chronic stress) playbacks.

In the anxious exposed chicks, there was a rapid drop in skin temperature followed by an overshoot as seen in the handling experiment. After the seventh playback, however, there was no thermal response, it appeared the chicks had tuned out to the calls.

In the depressed exposure chicks there was a similar response to the first playback as the anxious exposure, however, after the seventh playback, there was an overall increase by a degree in surface temperature, much like the increases found in depressed humans.

 

My opinions and how this will affect my future

I found this talk the most interesting and thought-provoking of all the seminars I have attended this semester. The thought of being able to improve the welfare of any animals is an exciting prospect. As well as its possible implications for the welfare of farm animals, it made me wonder whether this technology could be useful in animals in animal shelters as well as domesticated pets, so owners and workers can see how an animal is truly “feeling” when they are not around to observe. I would also be interested in looking at the effects of ecotourism on the stress levels of wild animals and wonder whether this less invasive technique could be used to monitor this.

 

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