Scientists using infrared thermography found that the eyes of the sheep are warming a little with the introduction of adrenaline in the blood. Temperature measurement eye can be a convenient non-invasive way of evaluating stress in livestock, although it is that variability still remain a more reliable indicator. It is also necessary to study the temperature changes of the eyes and other body parts in response to more natural stressors (e.g., pain), say the authors in PLoS ONE.
One of the indicators of the health of animals — their reaction to stress. Stress triggers a number of physiological changes in the body, including activation of the autonomic nervous system which regulates internal organs. To evaluate the autonomic nervous system can be different indicators: the level of catecholamines (e.g. adrenaline) in the blood, heart rhythm or its changes. The first option is inconvenient for monitoring the condition of the animals, since catecholamines are rapidly destroyed, and the blood sampling may cause additional stress. For heart rate measurements need to attach sensors to the animals, which can also affect physiology and behavior.
Another indicator that is affected by the activity of the autonomic nervous system — body temperature. Under stress the temperature rises, the surface of the animal’s body emits more heat energy and this change can be non-invasively registered using infrared thermography or thermal video.
A convenient object for temperature measurement by this method may be the eyes: it is not covered with hair, and in the lacrimal caruncle (the tissue in the corner of the eye) there is a dense network of capillaries, which regulates the sympathetic nervous system. Temperature changes of the eye in response to stress were already observed in different animals, in the sheep, however, the results of these studies are contradictory.
A group of researchers from New Zealand under the guidance of Gemma worth (Gemma Worth) and Mairi Stewart (Mairi Stewart) from the research center of animal husbandry in Ruakura using infrared thermography tested whether increases the temperature of the lacrimal caruncle with stress in sheep breed Romney and compared the convenience and sensitivity of this method with the measurement of your heart rate of animals. Before the experiment the sheep (there were 20) for two weeks to get used to the laboratory environment, the sensors and means for fixing the head. The day before the study the animals were shaved the hair on the chest and sides of the neck, then set heart rate sensors and two lines: one for the introduction of substances, the other for obtaining blood samples.