Regulation of heart rate and rumen temperature in red deer: effects of season and food intake

Analysis of Annual Changes in the Concentrations of Selected Macro- and Microelements, Thyroxine, and Testosterone in the Serum of Red Deer (Cervus elaphus) Stags

The aim of the study was to analyze seasonal changes in the concentrations of calcium, phosphorus, magnesium, and selenium as well as thyroxine and testosterone in adult red deer stags. The highest testosterone concentrations (mean 6.29±4.36 ng/ml) were observed from the end of August to November, confirming an increase in testicular secretory activity during the mating season. The changes in thyroxine concentration show circannual rhythms, most likely related to changes in the air temperature. The highest mean level of thyroxine was observed in spring (55.69±10.99 ng/ml). The concentration of selenium also reached the highest level during this season (0.107±0.027 μg/ml). In the case of the studied macroelements, the concentrations were stable from spring to summer but then decreased to the lowest mean values in autumn in both years of the experiment (Ca, 61.17±10.60; P, 47.08±9.59; Mg, 15.96±2.39 μg/ml). The dynamics of thyroxine secretion does not seem to affect directly the metabolism of calcium, phosphorus, and magnesium. In turn, sexual activity, manifested in the increase in secretion of testosterone, may affect changes in the concentration of calcium. Additionally, we cannot exclude a connection between changes in the concentrations of testosterone and selenium.

Reference intervals for hematology, serum biochemistry, and basic clinical findings in free-ranging Chinese Pangolin (Manis pentadactyla) from Taiwan

BACKGROUND

There are 8 species of Pangolins found in Asia and Africa. Among them, the Chinese Pangolin (Manis pentadactyla) is an endangered insectivorous mammal found only in Asia. Hematology and serum chemistry reference intervals are critical for evaluating an animal's well-being and can be useful for clinical diagnostic purposes. Currently, there are no such reference intervals available for any Pangolin species.

OBJECTIVE

The purpose of the present study was to establish reference intervals for hematology and serum biochemical analytes, and some basic clinical findings, in Chinese Pangolins.

METHODS

Reference intervals for the hematology and serum chemistry variables, and basic clinical findings (body weight, heart rate, body temperature, blood oxygen saturation) were collected from 100 clinically healthy Chinese Pangolins (51 males and 49 females) using parametric and nonparametric percentile methods. In addition, seasonal, age-related, and sexual differences for all variables were statistically analyzed.

RESULTS

No significant differences in the reference intervals were found between males and females, except for body weight. However, significant seasonal differences were observed for heart rate, body temperature, serum ALT and lipase activities, and phosphate concentrations. The variables, which were significantly different between adult and sub-adult Pangolins were heart rate, MCH, creatinine, total protein, phosphate, glucose, and potassium concentration, and amylase activity. Seasonal and age group differences should be taken into consideration when using these reference intervals.

CONCLUSIONS

The findings from the present study represent a valuable resource for assessing the health of Chinese Pangolins, and contribute toward the conservation of this endangered mammal.

Contrary seasonal changes of rates of nutrient uptake, organ mass, and voluntary food intake in red deer (Cervus elaphus)

Northern ungulates acclimatize to winter conditions with restricted food supply and unfavorable weather conditions by reducing energy expenditure and voluntary food intake. We investigated in a study on red deer whether rates of peptide and glucose transport in the small intestines are also reduced during winter as part of the thrifty phenotype of winter-acclimatized animals, or whether transport rates are increased during winter in order to exploit poor forage more efficiently. Our results support the latter hypothesis. We found in a feeding experiment that total energy intake was considerably lower during winter despite ad libitum feeding. Together with reduced food intake, mass of visceral organs was significantly lower and body fat reserves were used as metabolic fuel in addition to food. However, efficacy of nutrient absorption seemed to be increased simultaneously. Extraction of crude protein from forage was higher in winter animals, at any level of crude protein intake, as indicated by the lower concentration of crude protein in feces. In line with these in vivo results, Ussing chamber experiments revealed greater electrogenic responses to both peptides and glucose in the small intestines of winter-acclimatized animals, and peptide uptake into jejunal brush-border membrane vesicles was increased. We conclude that reduced appetite of red deer during winter avoids energy expenditure for unproductive search of scarcely available food and further renders the energetically costly maintenance of a large gut and visceral organs unnecessary. Nevertheless, extraction of nutrients from forage is more efficient in the winter to attenuate an inevitably negative energy balance.

Ecophysiology of Omega Fatty Acids: A Lid for Every Jar

Omega fatty acids affect various physiological functions, such as locomotion, cardiac function, and thermogenesis. We highlight evidence from animal models that points to pathways by which specific omega fatty acids exert differential effects. We suggest that optimizing the omega fatty acid composition of tissues involves trade-offs between costs and benefits of specific fatty acids.

"Seasonal changes in the neuroendocrine system": some reflections

This perspective considers first the general issue of seasonality and how it is shaped ecologically. It asks what is the relative importance of "strategic" (photoperiod-dependent) versus "tactical" (supplemental) cues in seasonality and what neural circuits are involved? It then considers recent developments as reflected in the Special Issue. What don't we understand about the photoperiodic clock and also the long-term timing mechanisms underlying refractoriness? Are these latter related to the endogenous annual rhythms? Can we finally identify the opsins involved in photodetection? What is the present position with regard to melatonin as "the" annual calendar? An exciting development has been the recognition of the involvement of thyroid hormones in seasonality but how does the Dio/TSH/thyroid hormone pathway integrate with downstream components of the photoperiodic response system? Finally, there are the seasonal changes within the central nervous system itself--perhaps the most exciting aspect of all.

Heterothermy in large mammals: inevitable or implemented?

Advances in biologging techniques over the past 20 years have allowed for the remote and continuous measurement of body temperatures in free-living mammals. While there is an abundance of literature on heterothermy in small mammals, fewer studies have investigated the daily variability of body core temperature in larger mammals. Here we review measures of heterothermy and the factors that influence heterothermy in large mammals in their natural habitats, focussing on large mammalian herbivores. The mean 24 h body core temperatures for 17 species of large mammalian herbivores (>10 kg) decreased by ∼1.3°C for each 10-fold increase in body mass, a relationship that remained significant following phylogenetic correction. The degree of heterothermy, as measured by the 24 h amplitude of body core temperature rhythm, was independent of body mass and appeared to be driven primarily by energy and water limitations. When faced with the competing demands of osmoregulation, energy acquisition and water or energy use for thermoregulation, large mammalian herbivores appear to relax the precision of thermoregulation thereby conserving body water and energy. Such relaxation may entail a cost in that an animal moves closer to its thermal limits for performance. Maintaining homeostasis requires trade-offs between regulated systems, and homeothermy apparently is not accorded the highest priority; large mammals are able to maintain optimal homeothermy only if they are well nourished, hydrated, and not compromised energetically. We propose that the amplitude of the 24 h rhythm of body core temperature provides a useful index of any compromise experienced by a free-living large mammal and may predict the performance and fitness of an animal.

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 intake on fasting heat production, respiratory quotient and plasma metabolites measured using the washed rumen technique

The objective was to investigate the effect of intake before fasting on concentrations of metabolites and hormones, respiratory quotient (RQ) and fasting heat production (HP) using the washed rumen technique and to compare these values with those from the fed state. Six Holstein steers (360±22 kg) were maintained at 21°C and fed three different energy intakes within a replicated 3×3 Latin square design with 21-day periods. Steers were fed alfalfa cubes to provide 1.0, 1.5 and 2.0×NEm during 19 days of each experimental period. Steers were placed in individual metabolism stalls fitted with indirect calorimetry head-boxes on day 20 of each experimental period (FED steers) and fed their normal meal. On day 21 of each period the reticulorumen was emptied, washed and refilled with ruminal buffer (NaCl=96; NaHCO3=24; KHCO3=30; K2HPO4=2; CaCl2=1.5; MgCl2=1.5 mmol/kg of buffer) aerated with 75% N2 and 25% CO2 before introduction to the rumen (steers were not fed; WASHED steers). Each gas exchange was measured over 24 h. HP for 1.0, 1.5 and 2.0×NEm were 479, 597 and 714 kJ/daykg0.75 (s.e.m. =16), respectively. The plateau RQ was 0.756, 0.824 and 0.860 for the 1.0, 1.5 and 2.0×NEm intakes for the FED steers, respectively. After rumen washing, fasting HP was 331, 359 and 400 kJ/daykg0.75 (s.e.m.=13) for 1.0, 1.5, and 2.0×NEm intakes before fasting, respectively. The RQ for WASHED rumen steers was 0.717, 0.710 and 0.719, respectively. Cortisol and β-hydroxybutyrate concentrations in WASHED rumen steers did not exceed threshold levels for severe energy deficit and stress as can be induced from prolonged fasting. This study demonstrates that a fasting state can be emulated using the washed rumen technique, minimizing the time required as opposed to traditional fasting methodologies, without causing a severe energy deficit and stress.

Adaptation to Heat and Water Shortage in Large, Arid-Zone Mammals

Although laboratory studies of large mammals have revealed valuable information on thermoregulation, such studies cannot predict accurately how animals respond in their natural habitats. Through insights obtained on thermoregulatory behavior, body temperature variability, and selective brain cooling in free-living mammals, we show here how we can better understand the physiological capacity of large mammals to cope with hotter and drier arid-zone habitats likely with climate change.

Body Temperature Predicts the Direction of Internal Desynchronization in Humans Isolated from Time Cues

This publication presents a new analysis of experiments that were carried out in human subjects in isolation from time cues, under supervision of Jürgen Aschoff and Rütger Wever at the Max Planck Institute for Behavioural Physiology (Erling-Andechs, Germany, 1964-1974). Mean rectal temperatures (tb) were compared between subjects who showed internal desynchronization (ID) and internal synchronization (IS) of the endogenous rhythms of sleep-wakefulness and of body temperature. The results showed that tb was reduced in long ID (circadian sleep-wake cycle length [τSW] > 27 h) and increased in short ID (τSW < 22 h) relative to IS. In subjects with both ID and IS sections in the complete record, these differences were also found when comparing only the IS sections: Low tb during IS predicts the later occurrence of long ID, and high tb predicts the incidence of short ID. While this association is associated with sex differences in tb, it also occurs within each sex. To the extent that the variation in tb reflects the variation in heat production (metabolic rate), the results are consistent with the proposition that the spontaneous frequency of the human sleep-wake oscillator is associated with the metabolic rate, as suggested on the basis of the proportionality of meal frequency and sleep-wake frequency. The finding thus has implications for our views on spontaneous sleep timing.

Social dominance is associated with individual differences in heart rate and energetic response to food restriction in female red deer

Energy expenditure is a key mechanism underlying animal ecology, yet why individuals often differ in metabolic rate even under identical conditions remains largely unexplained. Individual variation in metabolism might be explained by correlations with other behavioral and physiological traits, with individual syndromes having environment- or state-dependent costs and benefits to fitness. We tested whether social rank within herds of female red deer is associated with individual differences in resting heart rate, an index of metabolic rate, and energetic response to monthly periods of food restriction during winter in a large outdoor enclosure near Vienna, Austria. Social rank had a strong positive effect on average daily heart rate, independent of the effects of food intake, air temperature, body temperature, and body mass. Subordinate individuals had lower heart rates than dominants, and consequently they suffered lower rates of body mass loss during periods of restricted pellet food supply. A greater capacity to minimize energy requirements might benefit the survival of subdominant female red deer during periods of negative energy balance in winter. Our study provides empirical support in a large mammal for linkages in behavior and metabolism within individuals that have environment-dependent consequences to the energy budget.

Seasonal variation of activity patterns in roe deer in a temperate forested area

We investigated the activity patterns of a European roe deer (Capreolus capreolus) population living in a forested Apennine area in central Italy, in order to shed light on the environmental and biological factors that were expected to account for the observed activity patterns on daily and yearly bases. Daily and seasonal activity patterns of 31 radio-collared roe deer were assessed through sessions of radio tracking for a total period of 18 consecutive months. Roe deer showed bimodal activity patterns throughout the year, with the two highest peaks of activity recorded at dawn and dusk. Activity patterns of males and females differed during the territorial period (from early spring to late summer), whereas they did not during the nonterritorial period. Most likely, behavioral thermoregulation can be held responsible for variation of daily activity patterns in different seasons. In winter, for instance, activity during the dawn period was significantly higher than in other seasons and daylight activity was significantly higher than at night. Nocturnal activity was highest in summer and lowest in winter. During the hunting season, moreover, roe deer showed lower activity levels than during the rest of the year. The prediction that roe deer would show lower activity levels during full moon nights, when the predation risk was assumed to be higher, was not confirmed by our data. Activity rhythms in roe deer were thus subjected to both endogenous and environmental factors, the latter working as exogenous synchronization cues. Accordingly, in changing environmental and ecological conditions, a circadian cycle of activity could be seen as the result of complex interactions among daily behavioral rhythm, digestive physiology, and external modifying factors.