Alexander Riek

Adaptation strategies to seasonal changes in environmental conditions of a domesticated horse breed, the Shetland pony ( Equus ferus caballus )

SUMMARY Recent results suggest that the wild ancestor of the horse, the Przewalski horse, exhibits signs of a hypometabolism. However, there are speculations that domestic animals lost the ability to reduce energy expenditure during food shortage and adverse environmental conditions. Therefore, we investigated physiological and behavioural strategies employed by a robust domesticated horse breed, the Shetland pony, over the course of a year under temperate conditions by measuring ambient temperature (Ta), subcutaneous temperature (Ts), locomotor activity (LA), lying time, resting heart rate, body mass and body condition score. Ten animals were kept on pasture in summer and in open stables in winter; further, in winter the animals were allocated into one control and one feed-restricted group of five animals each to simulate natural seasonal food shortage. The annual course of the mean daily Ts of all horses showed distinct fluctuations from a mean of 35.6±0.5°C, with higher variations in summer than in winter. Diurnal amplitudes in Ts were highest (P<0.001) in April (12.6°C) and lowest in January (4.0°C), with a nadir around dawn and a peak around mid-day. The feed-restricted group had a significantly lower daily Ts compared with the control group on cold winter days, with Ta values below 0°C. Mean annual heart rate and LA followed Ta closely. Heart rate of the feed-restricted animals significantly decreased from a mean of 52.8±8.1 beats min–1 in summer to 29±3.9 beats min–1 in winter and differed from the control group (P<0.001). Mean daily LA was lowest at the end of winter (7000 activity impulses day–1) and highest in summer (25,000 activity impulses day–1). Our results show that Shetland ponies exhibit signs of a winter hypometabolism indicated by reduced heart rate and Ts. Thus, domesticated horses seem to have maintained the capacity for seasonal adaptation to environmental conditions by seasonal fluctuations in their metabolic rate.

Allometry of thermal variables in mammals: consequences of body size and phylogeny

A large number of analyses have examined how basal metabolic rate (BMR) is affected by body mass in mammals. By contrast, the critical ambient temperatures that define the thermo‐neutral zone (TNZ), in which BMR is measured, have received much less attention. We provide the first phylogenetic analyses on scaling of lower and upper critical temperatures and the breadth of the TNZ in 204 mammal species from diverse orders. The phylogenetic signal of thermal variables was strong for all variables analysed. Most allometric relationships between thermal variables and body mass were significant and regressions using phylogenetic analyses fitted the data better than conventional regressions. Allometric exponents for all mammals were 0.19 for the lower critical temperature (expressed as body temperature ‐ lower critical temperature), −0.027 for the upper critical temperature, and 0.17 for the breadth of TNZ. The small exponents for the breadth of the TNZ compared to the large exponents for BMR suggest that BMR per se affects the influence of body mass on TNZ only marginally. However, the breadth of the TNZ is also related to the apparent thermal conductance and it is therefore possible that BMR at different body masses is a function of both the heat exchange in the TNZ and that encountered below and above the TNZ to permit effective homeothermic thermoregulation.

Thermobiology, energetics and activity patterns of the Eastern tube-nosed bat (Nyctimene robinsoni) in the Australian tropics: effect of temperature and lunar cycle

SUMMARY Currently, there are no data on the thermal biology of free-ranging pteropodid bats (Chiroptera). Therefore, our aim was to investigate physiological and behavioural strategies employed by the fruit bat Nyctimene robinsoni (body mass ∼50 g) in winter in tropical Northern Queensland in relation to ambient temperature (Ta) and the lunar cycle. Daily body temperature (Tb) fluctuations in free-ranging bats were measured via radio-telemetry and metabolic rate was measured in captivity via open-flow respirometry (Ta, 15–30°C). Free-ranging bats showed a significant 24 h circadian cycle in Tb, with the lowest Tb at the end of the rest phase just after sunset and the highest Tb at the end of the activity phase just before sunrise. Average daily core Tb ranged from 34.7±0.6 to 37.3±0.8°C (mean ± s.d.) over an average daily Ta range of 17.1±1.1 to 23.5±1.8°C. Tb never fell below 30°C but Tb was significantly reduced during the full moon period compared with that during the new moon period. Tb was correlated with Ta during the second half of the rest phase (P<0.001) but not during the active phase. Resting metabolic rate of bats was significantly affected by Ta (P<0.001, R2=0.856). Our results show that tube-nosed bats exhibit reduced Tb on moonlit nights when they reduce foraging activity, but during our study torpor was not expressed. The energy constraints experienced here by tube-nosed bats with relatively moderate Ta fluctuations, short commuting distances between roosting and feeding locations, and high availability of food were probably not substantial enough to require use of torpor.

Developmental phenotypic plasticity in a marsupial

SUMMARY Climate change is likely to substantially affect the distribution ranges of species. However, little is known about how different mammalian taxa respond morphologically and physiologically to a rapid change of climate. Our objective was to provide the first quantitative data on the effect of continuous cold exposure during development on morphological and functional variables of a marsupial. Fat-tailed dunnarts (Sminthopsis crassicaudata, Dasyuridae) were reared at an ambient temperature (Ta) of 16°C [cold-reared (CR)] or 22°C [warm-reared (WR)] until they reached adult age (>200 days). Body and head length of CR animals were significantly longer than in WR animals (mean ± s.e.m.; body: CR 80.8±6 mm, WR 76.4±5 mm; head: CR 29.4±3 mm, WR 27.5±2 mm), but other body attributes were not significantly different. Use of torpor was more frequent, torpor bout duration was longer and average daily metabolic rate and percentage of savings when using torpor were significantly higher (P<0.01) in CR than in WR animals at 16°C Ta but not at 24°C. Furthermore, resting metabolic rates measured at 16°C Ta were significantly lower in CR than WR animals; at 30°C Ta values were similar. Our results do not conform to Allen’s rule, but to some extent they do conform to Bergmann’s rule. However, the data demonstrate that a relatively moderate cold exposure from birth until adulthood induces marked changes in the morphology and thermal energetics of small marsupials. Such short-term phenotypic responses without the need for long-term selection are likely important for the ability to cope with different climates over a wide range of distribution, but will also play a crucial role in enhancing the survival of species during climate change.

Saving energy during hard times: Energetic adaptations of Shetland pony mares

Recent results suggest that wild Northern herbivores reduce their metabolism during times of low ambient temperature and food shortage in order to reduce their energetic needs. It is, however, not known whether domesticated animals are also able to reduce their energy expenditure. We exposed 10 Shetland pony mares to different environmental conditions (summer and winter) and to two food quantities (60% and 100% of maintenance energy requirement) during low winter temperatures to examine energetic and behavioural responses. In summer, ponies showed a considerably higher field metabolic rate (FMR; 63.4±15.0 MJ day–1) compared with food-restricted and control animals in winter (24.6±7.8 and 15.0±1.1 MJ day–1, respectively). During summer, locomotor activity, resting heart rate and total water turnover were considerably elevated (P<0.001) compared with winter. Animals on a restricted diet (N=5) compensated for the decreased energy supply by reducing their FMR by 26% compared with control animals (N=5). Furthermore, resting heart rate, body mass and body condition score were lower (29.2±2.7 beats min–1, 140±22 kg and 3.0±1.0 points, respectively) than in control animals (36.8±41 beats min–1, 165±31 kg, 4.4±0.7 points; P<0.05). While the observed behaviour did not change, nocturnal hypothermia was elevated. We conclude that ponies acclimatize to different climatic conditions by changing their metabolic rate, behaviour and some physiological parameters. When exposed to energy challenges, ponies, like wild herbivores, exhibited hypometabolism and nocturnal hypothermia.

Effect of water restriction on drinking behaviour and water intake in German black-head mutton sheep and Boer goats

The present study was conducted to evaluate and compare the physiological responses of sheep and goats to water restriction using the deuterium dilution technique (D2O) to predict the total water intake (TWI) in both species. In two consecutive trials, 10 non-lactating Boer goats and 10 non-lactating German black-head mutton ewes were each randomly allocated into a treatment and a control group. In the control groups (n = 5, for each species), water was offered ad libitum, whereas the treatment groups (n = 5, for each species) received water 3 h/day on experimental days 8 to 14 and 6 h every 2 days on experimental days 15 to 22. The respiratory rate, rectal temperature, body mass and drinking behaviour were also recorded. The TWI was estimated by D2O for each animal. Water restriction for 21 h/day or 42 h/2 days had no significant (P > 0.05) effect on water intake (WI), feed intake, WI to dry matter intake ratio or body mass in both species. The absence of differences between species in their WIs was also confirmed using D2O. However, sheep had higher respiratory rates and rectal temperatures than goats in both control and treatment groups. Both species showed the ability to tolerate a moderate water shortage by activating several physiological mechanisms and behavioural strategies.

Effect of shearing on water turnover and thermobiological variables in German Blackhead mutton sheep

Current equations for estimating water requirements in sheep do not differentiate between shorn and unshorn sheep. Furthermore, the effect of shearing on thermoregulative responses in sheep has not been adequately studied under temperate environmental conditions. Therefore, the present study was conducted to investigate the effect of wool coverage on water turnover in relation to thermoregulation in sheep by using the deuterium dilution technique to predict total water intake before and after shearing. Physiological responses, such as water turnover, surface temperature, and rectal temperature, as well as drinking behavior of sheep were also evaluated. Fourteen nonlactating German Blackhead mutton ewes were randomly allocated into 2 groups: a control group (n = 7) that was already shorn, and a treatment group (n = 7) that was left unshorn (wool length: 10.6 ± 1.2 cm). Individual feed and water intakes were recorded throughout the experiment (d 1 to 71). Two weeks after measurements commenced (d 15), treatment sheep were shorn. Water intake was estimated twice for 2 consecutive weeks by using deuterium dilution techniques (d 1 to 15 and d 57 to 71). Ambient temperature (T(a)), relative humidity, and respiratory rate were measured daily, whereas BW, rectal and animal surface temperatures (using infrared thermography), and wool length were measured weekly. In the first 2 wk, when treatment sheep were unshorn, treatment and control ewes differed (P < 0.05) in DMI (52 ± 4 vs. 59 ± 4 g·kg(-0.75)·d(-1)), water intake (165 ± 17 vs. 134 ± 18 g·kg(-0.75)·d(-1)), respiratory rate (66 ± 5 vs. 31 ± 4 breath/min), rectal temperature (39.3 ± 0.2 vs. 38.8 ± 0.1°C), and surface temperatures (body side: 19.3 ± 0.3 vs. 24.5 ± 0.6°C; leg: 25.8 ± 2.4 vs. 27.4 ± 1.6°C). However, after shearing, these differences partly disappeared. The same trend in water intake between groups was confirmed using the isotope dilution technique. We found a significant relationship between T(a) and water intake, respiratory rate, and body surface temperatures. Even under temperate conditions (T(a) < 28°C), shearing significantly reduced core body temperature, water intake, and respiratory rate in German Blackhead mutton sheep, thus indicating heat stress in fleeced animals, which should be considered when determining the optimal shearing time in sheep as well as when estimating water requirements.

Deuterium oxide dilution accurately predicts water intake in sheep and goats

The aim of this study was to test whether the deuterium oxide dilution technique accurately predicts water intake in sheep and goats. Two other issues were also studied: (i) a comparison of water intake in sheep and goats and (ii) an assessment of whether observations of drinking behaviour can accurately measure the water intake. In this study, eight dry Boer goats and eight dry German Black Head Mutton ewes were kept under controlled stable conditions. Animals had access to hay and water ad libitum. Diurnal drinking behaviour was recorded by video. Individual daily water intake was measured and estimated for 2 weeks by re-weighing water buckets and from water kinetics using the deuterium oxide dilution technique, respectively. In addition, dry matter intakes were directly measured and were significantly higher in sheep than in goats. The average daily water consumption by drinking differed significantly between the two species, with higher intakes in sheep than in goats. Total body water expressed as a percentage of body mass did not differ between species. Measurement methods of total water intake (TWI) using deuterium oxide dilution and re-weighing water buckets did not differ significantly in both species (P = 0.926). Results obtained for measured and estimated TWI confirm that the isotope dilution technique gives reliable results for estimates of water intake in sheep and goats. The higher amount of water intake in sheep was also reflected by their drinking behaviour. Sheep spent approximately 0.3% per 24-h drinking, while Boer goats spent only 0.1%. However, measured and estimated TWIs were only moderately correlated to the daily time spent drinking. The lower water intake found in Boer goats confirms a superior water management capacity compared with Black Head Mutton sheep even under temperate conditions.

Thyroid hormones correlate with field metabolic rate in ponies, Equus ferus caballus

ABSTRACT During winter, free-living herbivores are often exposed to reduced energy supply at the same time that energy needs for thermoregulation increase. Several wild herbivores as well as robust horse breeds reduce their metabolism during times of low ambient temperature and food shortage. Thyroid hormones (THs) affect metabolic intensity and a positive effect of THs on basal metabolic rate (BMR) has been demonstrated in mammals and birds. As BMR and field metabolic rate (FMR) are often assumed to be intrinsically linked, THs may represent a reliable indicator for FMR. To test this hypothesis, 10 Shetland pony mares were kept under semi-extensive central European conditions. During the winter season, one group was fed 60% and one group 100% of their maintenance energy requirements. We measured FMR, locomotor activity, resting heart rate and TH levels in summer and winter. FMR, locomotor activity, resting heart rate and total T3 concentrations decreased substantially in winter compared with summer, whereas total T4 increased. Food restriction led to a reduced FMR and resting heart rate, while THs and locomotor activity were not affected. Across both seasons, FMR, resting heart rate and locomotor activity were positively correlated with total T3 but negatively and more weakly correlated with total T4. Summary: Thyroid hormones and energy expenditure are correlated in a semi-free-living ungulate.

Effect of long-term feed restriction on the health status and welfare of a robust horse breed, the Shetland pony (Equus ferus caballus)

Outdoor group housing is increasingly recognized as an appropriate housing system for domesticated horses. The objective of this study was therefore to investigate the effect of potential feed shortage in semi-natural horse keeping systems in winter on animal health and welfare. In 10 female Shetland ponies blood concentrations (NEFA, total protein (TP), total bilirubin (TB), beta-hydroxybutyrate (BHB) and thyroxine (T4)), body mass and the body condition score (BCS) were monitored for 7 months including a 4 months period of feed restriction in five of the 10 ponies. Restrictively fed animals lost 18.4±2.99% of their body mass and the BCS decreased by 2.2±0.8 points (BCS scale: 0=emaciated, 5=obese). Feed restriction led to a continuous increase in TB (P<0.001) and NEFA (P<0.01) concentrations compared to control ponies. The TP and BHB values only differed at the end of the trial with lower concentrations in restricted fed mares (P<0.05). Feed restriction had no effect on thyroxine concentrations. TB concentrations in the feed restricted group were out of the reference range during the entire feeding trial. The increased NEFA concentrations in feed restricted compared to control ponies suggest that fat was mobilized. The BCS, as well as plasma NEFA and TB concentrations were good indicators for a rapid detection of possible health problems caused by undernourishment in horses when kept under semi-natural conditions. In contrast, blood parameters of the control animals were within the reference ranges, suggesting that a year round outdoor housing with additional feed supply is an adequate housing system for a robust horse breed like the Shetland pony.