Abstract

A preliminary report of the use of infrared-thermography in zoo and wild animals was given by Eulenberger at the thirty-sixth International Symposium on the Diseases of Zoo and Wild Animals.² In this report, new areas of application of infrared light, measurement of normal body surface temperature pictures and alterations through inflammations, are presented.

Thermography offers the possibility to investigate an animal from a distance of one to a maximum of 20 m without having to sedate or anesthetize the animal. This technique measures the heat-radiation (between 3 and 5 µm wavelength) a body reflects on a surface into the environment.

Methods

The infrared-camera THERMOVISION 550 from AGEMA is cooled electrically to -80°C. The lens has a silicon surface, a semiconductor, which converts infrared radiation into photo-optical signals in an optimum way. This signal is then converted to digital black and white pictures, which then can be converted into color.³

At a wavelength of 10^-4 to 10^-6 λ/m and a frequency of 10¹⁴ Hz infrared-cameras today are able to differentiate surface-temperatures of 0.1°C.^1,2,5 High resolution monitors and computer-graphic hardware produce an accordingly precise presentation of the pictures. Measurements are only executed in the long wave band, since these rays are not damped so quickly in their intensity as short waved ones, so that measured values can be achieved over long distances. Long wave infrared radiation (λ=3–5 µm) is reflected by a coefficient of emission ϵ_s of nearly 1 from hairless skin, which is comparable to a black body.⁶ Due to the more or less thick hair of animal bodies thermography has its limits.² In eggs these problems do not exist.

The best results can be achieved if the investigated structure is placed within a region of 2 cm under the skin-surface, which applies, for example, to skin-tumors and abscesses. But also, greater structures situated deeper inside a body can be investigated with infrared, as long as they transmit heat to the surface, which then is measured as heat-area or -spots.³ This feature is used here to diagnose pregnancies in mammals or investigate avian or reptilian eggs for growth or fertilization.

In thermoregulatory processes, small inflammations or heat-producing tumors, more or less heat is transmitted to the body surface, so that in a thermogramm a temperature difference can be measured.^1,3 In the thermogramm, yellow and red colors show warmer areas, green and blue cooler areas. In black and white graphic representations, the warmer areas are light, the cooler dark. In human medicine infrared thermography is mainly used in neurology, orthopedic diagnostics, rheumatology, oncology (especially skin- and mammatumor-diagnostic), as well as in pain research.¹

Results

In the search of new noninvasive technologies in veterinary medicine, at the Zoological Garden of Berlin and Leipzig, Germany, we started a new research project with the goal of developing an easy-to-apply method for pregnancy diagnosis in zoo animals. Our preliminary results with using this new method revealed, that animals with no or short hair are well-suited for this technique. A uterus filled with a fetus and its fluids will be in contact with the body surface layers. The fetus produces heat from its metabolism that the mother has to cope with and try to eliminate. The shortest way of doing this is the direct way through the muscle and skin layers to the outside. In animals where there is no hair (e.g., rhinoceros) or short hair (e.g., giraffes) on the outside to prevent thermoregulation, the uterine heat can escape directly to the surface. In animals, with a lot of hair on the surface (e.g., camels) the method is, as of now, not applicable, because these animals thermoregulate entirely via the inside of their legs and the ventral body surface.

Another handicap with this technique is the lack of knowledge concerning the anatomic base of thermoregulation in exotic animals. For example, in babirusas, there seem to be thermoregulatory heat windows on the body surface, specific to each individual.

This technique was used on several zoo animals and the results are described below. Individual diagrams are provided during presentation of these results.

Pregnancy diagnosis in black rhinoceros (Diceros bicornis). Diagram 1 illustrates the approximate location of the uterus with an 11-mo-old rhinoceros fetus in situ. Diagram 2 shows a non-pregnant black rhinoceros. Diagrams 3–5 show a pregnant black rhinoceros. In diagram 3 the female is approximately 6 mo pregnant, in diagram 4 approximately 9 mo, and in diagram 5 approximately 11 mo. The diagrams show the volume increase of the uterus as the fetus grows over time. The light-colored area indicates the heat transmission area of the uterus to the body surface. Over time, the heat transmission area grows larger, because greater parts of the uterus come in contact with the body surface. Towards the end of pregnancy, the heat area covers the entire main body surface.

Pregnancy Diagnosis in Elephants (Elephas maximus)

Diagram 6 illustrates the approximate location of a 20-mo-old fetus in situ. Diagram 7 shows a non-pregnant elephant cow, diagram 8 an approximately 15-mo, and diagram 8 an approximately 20-mo pregnant cow. At mid-pregnancy, the animal shows a higher body temperature and also a local heat area on one or both sides of the body. In late pregnancy, the local heat area becomes less obvious as the uterus spreads over a large body surface area and hence the cow must put more general effort into thermoregulation and is not able any more to give up heat just locally.

Egg Control in Reptiles and Birds

As an attempt to observe the continuous growth of reptiles and birds inside their eggs, infrared thermography also showed its usefulness. In birds, the infrared heat measurement gives a quick overview over great amounts of eggs from either the incubator or natural sitting birds, when they rise from their nest. In reptiles it is especially important to be able to look at the thin-shelled eggs without having to touch them. In diagram 9, eggs are shown from a shelf of an incubator 3 min after removal from the incubator. Intact eggs are able to keep their temperature more constant to that of the incubator than are unfertilized or dead eggs. In reptiles, the area not covered by the hatching-material is available for temperature measurement with the infrared camera. Here the same principles apply as do in bird eggs: eggs with live embryos show higher temperatures then do those with dead embryos or unfertilized eggs. Diagram 10 shows the eggs of Heloderma spp. in an incubator box partially covered by hatching material. The dark area inside the eggshell indicates that it is not a live egg.

Discussion

As the results presented above indicate, infrared-thermography is a useful technique for zoo and wild animal medicine.⁴ It could be used for population management in rhinoceros and elephants by helping the wildlife biologist or veterinarian to diagnose pregnancies at a distance and hence give a better overview of happenings in populations. To date, the method is still in the process of being standardized, but once this is concluded, it is obviously a very useful tool in zoo and wildlife medicine. No narcosis or sedation is necessary to do this test and hence it is well suited for flighty animals as well. The only disadvantage is the limits to species with short or no hair. Also, the person using this method has to learn to differentiate between surface structures, such as slight scratches, intense sunshine, or wet areas, etc., and true heat areas from uterus thermoregulation. Once the method is established, the distance to the object can be increased and tele-lenses used. The method for investigating bird eggs, especially thick- or dark-shelled ones, as well as reptilian eggs seems to be another useful application of this technique. It allows for observation of many eggs at once as well as allowing one to look at eggs from naturally sitting birds when they rise from the nest. This gives new possibilities for population management and gaining of easy information concerning rates of pregnancies in mammals, and fertilization in birds and reptiles. Finally, this would be a method to acquire more basic data concerning the reproductive biology and performance of wild animals.

(VIN editor: No diagrams are available as of 4-23-21.)

Literature Cited

1.  AGEMA. 1996. Medizinische Thermographie, AGEMA Infrared Systems, Darmstadt, Germany, 2 Pp.

2.  Eulenberger K, Kämpfer P. Die Infrarotthermographie bei Zoo - und Wildtieren-erste Erfahrungen. Verh ber Erkrg Zootiere 36: 181–183.

3.  Felix R, Ramm B. 1988. Das Röntgenbild. Thieme Verlag, Stuttgart, 195–197.

4.  Hilsberg S, Göltenboth R, Eulenberger K. 1997. Infrarot-Thermografie bei Zootieren: Erste Erfahrungen im Einsatz zur Trächtigkeitsdiagnostik. Verh ber Erkrg Zootiere 38: 187–190.

5.  Orear J. 1985. Infrarot-Strahlungen. In: Orear J: Physik. Carl Hauser Verlag München, Wien, 224–228.

6.  Schmidt RF, Thews G. 1990. Wärmestrahlungen. In: Schmidt RF, Thews G: Physiologie des Menschen, Springer Lehrbuch, Berlin, Heidelberg, 666–668.