Seasonal variations and responses to normal activity of the deep body temperature in the Svalbard reindeer (Rangifer tarandus platyrhynchus)

Deep body temperature was recorded in two female Svalbard reindeer during summer and winter. The reindeer were subjected to naturally occurring weather, photoperiod and stimuli in outdoor pens on Svalbard. A telemetry system was employed using transmitters ingested into the rumen. Mean deep body temperature was 0.3°C higher in winter and while the animals were lying down. This suggests a different strategy for thermoregulation than that employed by other reindeer subspecies.


Introduction
The Svalbard reindeer is found on the high arctic Svalbard Archipelago, between 77° and 81° N.Lat. Mean monthly air temperatures are below 0°C for most of the year, strong winds are common and the sun is below horizon for over 4 months. To maintain a constant deep body temperature (Tdb) in this cold climate these reindeer employ various means for reducing heat loss. Morphological adaptations such as their small appendage size and thick pelt, as opposed to other reindeer races have been described by many and may assist in reducing heat loss. Still, relatively little is known about the Tdb of these animals.
The Tab of caribou calves (R. t. tarandus) was studied by McEvan et al. (1965) and observed to be 39°±0.78°C. Later the Tdb for non-exercising and exercising adult reindeer (R t. tarandus) was recorded by Hammel et al. {\972) as 38.4°±0.2°C and 39.2°±0.1°C respectively. Yousef and Luick (1975) reported Tdi/s between 38.4° and 38.8°C from yearling reindeer (R. tarandus) in ambient temperatures of 10° to 30°C. Segal (1983) and Segal and Ignatov (1974) investigated the Tdb of adult reindeer (R. t. tarandus) and found a 0.3°C reduction during winter. Cermnych and Visneveckaja (1980) studied adult reindeer (R. t. tarandus) during late winter and reported Tab's of 38.3°±0.01°C, with fluctuations from 38.0 to 38.8°C. They also stated that the Tdb of 16 animals dropped to 37.7±0.02°C in response to a 16°C decrease in ambient temperature, which occurred over 12 hours. This suggests an inertia in the regulatory system's response to decreased Tab's. Also, the above information indicates that there are seasonal deep body temperature differences, differences between calves and adults and from rest to exercise.
Since there was no published literature on Tdb in Svalbard reindeer (7?. t. platyrhynchus), a study seemed warranted. The present work investigated for seasonal variations in Tdb, and the possible relationship between Tdi and their normal lethargic movements and resting.

Methods and materials
Seasonal variations and responses to normal activity of Tab were investigated by the remote monitoring of two tame female reindeer, Fi and F2, subjected to naturally occurring weather, photoperiod and stimuli in outdoor pens.
Activity observations recognized only two activity levels 1) resting and 2) active. «Resting» meant lying down. During the winter resting was always in the curled up, legs under, round ball posture. «Active» included all activities where the reindeer were on their feet, eg. standing, walking, grazing. All such movement was usually lethargic.
Measurements of Tab and observations of activity were recorded hourly for a minium of 96 continuous hours during an observation period. Observation periods were in February, March and December for both Fi and F2, while for F2 July and August were also included. In addition, during December, February and March, the animals were continually observed between measurements to ascertain the length of time they spent resting.
Deep body temperature was actually rumen temperature, measured using SINTEF temperature sensitive radio transmitters (SINTEF Reguleringsteknikk, 7034 Trondheim) which were ingested. These thermistor temperature sensors had an accuracy of ±0.2°C and were Teflon coated cylinders, with length 50 mm and diameter 20 mm. The transmitters responded to changes in temperature by altering signal-pulse frequency, which was detected by an FM radio. A stop watch was used to measure the time taken to record 50 signals. The Tab was then read from the calibration chart for that transmitter. Calibration of transmittors before use was done by the SINTEF office. Body temperatures were always measured at least three times. The mean from these three was taken as the Tab for that measurement.
Traditionally deep body temperatures are measured by rectal probe. To help evaluate this study's results to those of previous studies, comparison measurements of rectal and rumen temperature were taken simultaneously at 5 different ambient temperatures (-20°, -2°, 5°, 11° and 23°C).
Comparison of sample means was done by computing "t" for unpaired series of samples from two populations, a "t" test with no assumptions made as to equality of the variance (Snedecor and Cox, 1967). All temperature means are given with their standard error of the mean. The ±0.2°C accuracy error of the sensors became intrinsic within the standard deviation for individual measurements and standard error of the mean due to the volume of samples.

Results
Mean Tab for Fi, at age 4 months, was 39.14±0.07°C, (mean ambient temperature -3°C). The mean Tab for Fi and F2, from 12 to 18 months of age, was 38.83±0.05°C.
The mean of all resting values for Fi and F2 combined was 38.92±0.02°C(n = 530). Similarly the mean for all activity values was 38.73±0.02°C (n = 360). The difference between these means was also significant (P<0.001).
Examined each month, the mean Tab's for resting are higher than mean Tab's for activity (Fig. 1), but the difference was not always statistically significant. For Fi there was a significant difference between the mean Tab's for resting and activity, in the months of December and March (P<0.001 and P<0.002 respectively). For F2 significant differences occurred in February and March (P<0.01 and P<0.001 respectively) (Fig. 1).
During December, February and March significant differences between resting and active Tab's were found when the animals rested continuously (no activity between the hourly observations) for 1 or more hours. The mean Tab for rest and activity combined was 38.83±0.05°C. However the mean Tab for activity occurring in the hour just prior to continuous rest was 38.68±0.07°C (Fig. 2). After one hour of continuous rest, the mean Tab was 39.01±0.04°C (Fig. 2) between the initial active Tab and the Tab following continuous rest of 1 more hours was statistically significant (P<0.001). There were no significant differences (P<0.05) among the resting means shown in fig. 2, though each by itself, was significantly different from the initial active Tab (P<0.001 for 1, 2, and 3 hours rest; P<0.02 for 4 hours and P<0.05 for 5/6 hours). The mean rectal Tab was always lower than mean rumen Tab at all 5 ambient temperatures tested. The difference between the two was least, 0.3°C, at ambient temperatures above 0°C. At ambient temperatures of -2° and -20°C the temperature difference was 1.0° and 1.6°C respectively. All differences were significant (P<0.05).

Discussion
Deep body temperatures measured were rumen temperatures. When rumen and rectal measurements were compared mean rectal Tab was always lower than mean rumen Tab. The temperature difference perhaps can be accounted for by rumen microbial activity providing a fermentation heat increment thereby elevating all Tab measurements. Heat production of rumen ingesta can be as high as (0.09kcal/hr)/kg body wt. (Hammel et al., 1962). However, the temperature difference between rumen and rectal means was not constant (being greater at ambient temperatures below 0°C) suggesting that rumen microbial activity may not be the only factor operating.
Snow ingestion affected only 9 out of the 100's of individual measurements within the study and were considered insignificant in affecting overall temperature means.
Mean Tab was 38.83°±0.05°C for normal activity and resting combined, in reindeer aged 12 to 18 months. These results were higher than the 38.4°C for adults from the study by Hammel et al. (1972). The presence of a fermentation increment might account for some of this difference. However, Yousef and Luick (1975), reported Tab's of 38.4 to 38.8°C for yearlings (Table 1).
Observed deep body temperatures were surprisingly higher when the animals were resting than when active. Mean deep body temperature rose 0.3°C and stabilized at " «active» for this study was all normal lethargic activity; for other studies «active» meant non-exercise.
~39.0°C (Fig. 2) when lying down for 1 or more hours in winter (unfortunately summer data concerning lying down was not available). This increase was probably due to a reduction in total conductance as a result of the «round ball» resting posture. Thus small Tab increases, within the ranges measured, seen to be tolerated without any metabolic adjustment being made to keep Tab strictly constant. The Tab rise indicates an inertia in the regulatory system. Cermnych and Visneveckaja (1980) also found indication of inertia within the system, but in their study it was for Tab decreases.
Mean Tab was highest in winter and lowest in summer. The winter rise of 0.3°C in mean Tab may not be accounted for by rumen fermentation rate, as this is lower in winter, due to reduced food intake. If the fermentation heat increment was important, one would expect a winter decrease I rumen Tab and a summer increase. Instead this winter increase can most probably be accounted for by the extremely thick and long winter pelt providing a much lowered fur conductance, as opposed to the summer pelt, for the same amount of the heat production. Thus even with the cold winter air temperatues considered, the winter fur conductance is so low as to cause Tab to rise as heat loss is reduced. The Tab increase need not be a result of increased metabolism. In fact Segal (1983) reported a 25% reduction in winter metabolic rates for reindeer and Nilssen (1984) studying Svalbard reindeer, observed reductions in the winter resting metabolic rate. Nilssen (1984) suggested the reductions were due to the animal's decreased winter feed intake and not the result of a physiological adaption. The winter rise in mean Tab's may also be to some extent affected by the Svalbard reindeer's very low level of locomotor activity in winter. Cuyler (1984) found that the same two reindeer studied spent 65% of their time resting i winter. Since the present study has shown mean Tab was highest while resting, this lack of winter movement may be of importance for thermoregulation and contribute to the high winter Tab mean.
In contrast to this study's 0.3°C winter increase in mean Tab, work by Segal (1983) and Segal and Ignatov (1974) reported a 0.3°C winter reduction in Tab for R. t. tarandus (Table 1). This difference may have been caused by experimental methods or may be the result of different strategies for thermoregulation being employed by these two subspecies of reindeer. It is difficult to describe a strategy for the reindeer used in Segal (1983) and Segal and Ignatov's (1974) studies without more information. However from observation, the winter strategy of Svalbard reindeer seems to include a thick insultative pelt, little activity and much rest in curled round ball posture (65% of the time). The resting posture by reducing overall conductance, enables the animal to maintain Tab without the expence of extra work or metabolism.