Cutaneous Evaporative Heat Loss Research Articles

Phenotypic flexibility in heat production and heat loss in response to thermal and hydric acclimation in the zebra finch, a small arid-zone passerine

To maintain constant body temperature (Tb) over a wide range of ambient temperatures (Ta) endothermic animals require large amounts of energy and water. In hot environments, the main threat to endothermic homeotherms is insufficient water to supply that necessary for thermoregulation. We investigated flexible adjustment of traits related to thermoregulation and water conservation during acclimation to hot conditions or restricted water availability, or both, in the zebra finch, Taeniopygia guttata a small arid-zone passerine. Using indirect calorimetry, we measured changes in whole animal metabolic rate (MR), evaporative heat loss (EHL) and Tb before and after acclimation to 23 or 40 °C, with different availability of water. Additionally, we quantified changes in partitioning of EHL into respiratory and cutaneous avenues in birds exposed to 25 and 40 °C. In response to heat and water restriction zebra finches decreased MR, which together with unchanged EHL resulted in increased efficiency of evaporative heat loss. This facilitated more precise Tb regulation in heat-acclimated birds. Acclimation temperature and water availability had no effect on the partitioning of EHL into cutaneous or respiratory avenues. At 25 °C, cutaneous EHL accounted for ~ 60% of total EHL, while at 40 °C, its contribution decreased to ~ 20%. Consistent among-individual differences in MR and EHL suggest that these traits, provided that they are heritable, may be a subject to natural selection. We conclude that phenotypic flexibility in metabolic heat production associated with acclimation to hot, water-scarce conditions is crucial in response to changing environmental conditions, especially in the face of current and predicted climate change.

Physiological Responses and Lactation to Cutaneous Evaporative Heat Loss in Bos indicus, Bos taurus, and Their Crossbreds.

Cutaneous evaporative heat loss in Bos indicus and Bos taurus has been well documented. Nonetheless, how crossbreds with different fractional genetic proportions respond to such circumstances is of interest. A study to examine the physiological responses to cutaneous evaporative heat loss, also lactation period and milk yield, were conducted in Sahiwal (Bos indicus, n = 10, 444±64.8 kg, 9±2.9 years), Holstein Friesian (Bos taurus, HF100% (n = 10, 488±97.9 kg, 6±2.8 years)) and the following crossbreds: HF50% (n = 10, 355±40.7 kg, 2±0 years) and HF87.5% (n = 10, 489±76.8 kg, 7±1.8 years). They were allocated so as to determine the physiological responses of sweating rate (SR), respiration rate (RR), rectal temperature (RT), and skin temperature (ST) with and without hair from 06:00 h am to 15:00 h pm. And milk yield during 180 days were collected at days from 30 to 180. The ambient temperature-humidity-index (THI) increased from less than 80 in the early morning to more than 90 in the late afternoon. The interaction of THI and breed were highly affected on SR, RR, RT, and ST (p<0.01). The SR was highest in Sahiwal (595 g/m2/h) compared to HF100% (227 g/m2/h), and their crossbreds both HF50% (335 g/m2/h) and HF87.5% (299 g/m2/h). On the other hand, RR was higher in HF87.5% (54 bpm) and both HF100% (48 bpm) and HF50% (42 bpm) than Sahiwal (25 bpm) (p<0.01). The RT showed no significant differences as a result of breed (p>0.05) but did change over time. The ST with and without hair were similar, and was higher in HF100% (37.4°C; 38.0°C) and their crossbred HF50% (35.5°C; 35.5°C) and HF87.5% (37.1°C; 37.9°C) than Sahiwal (34.8°C; 34.8°C) (p<0.01). Moreover, the early lactation were higher at HF100% (25 kg) and 87.5% (25 kg) than HF50% (23 kg) which were higher than Sahiwal (18 kg) while the peak period of lactation was higher at HF100% (35 kg) than crossbreds both HF87.5% and HF50% (32 kg) which was higher than Sahiwal (26 kg) (p<0.05). In conclusion, sweating and respiration were the main vehicle for dissipating excess body heat for Sahiwal, HF and crossbreds, respectively. The THI at 76 to 80 were the critical points where the physiological responses to elevated temperature displayed change.

Differences of skin morphology in Bos indicus, Bos taurus, and their crossbreds

Cutaneous evaporation is the main avenue by which cattle dissipate heat via the involvement of sweat glands and other skin components. The difference in skin morphology between B. indicus and B. taurus has been recognized, as well as differences in their ability to tolerate heat. The objective of this study was to compare skin morphology between B. indicus, B. taurus, and their crossbreds. Skin samples of Sahiwal (B. indicus) (n=10, reddish brown skin) and Holstein Friesian (HF) (B. taurus) (n=10, black and white skin) and crossbred of HF75% (n=10, black and white skin) and HF87.5 % (n=10, black and white skin) were biopsied for histological study, followed by measurement of skin components. The results indicated that breed significantly affected sweat gland morphology. The shape of the sweat gland, as indicated by the ratio of length/diameter, in Sahiwal was baggier in shape compared to HF (5.99 and 9.52) while values for crossbreds were intermediate (7.82, 8.45). The density and volume of sweat glands in Sahiwal (1,058 glands/cm(2); 1.60 μ(3) × 10(-6)) were higher than in HF (920 glands/cm(2); 0.51 μ(3)x10(-6)) and crossbreds, both HF 75 % (709 glands/cm(2); 0.68 μ(3) × 10(-6)) and HF 87.5 % (691 glands/cm(2); 0.61 μ(3) × 10(-6)) respectively. However, capillary surface area was greater for HF (2.07 cm(2)) compared to Sahiwal (1.79 cm(2)); accordingly, the lower genetic fraction of HF in crossbred cattle showed less capillary surface area (1.83 and 1.9 cm(2) for HF75% and HF87.5 %) (P<0.01). Nerve density was not significantly different between Sahiwal and HF but was higher in the crossbred (P<0.01) cattle. Moreover, the effect of skin color (black and white) was evaluated and it was found that there was an interaction (P<0.01) between breed and skin color on the skin components. This study reveals that there are differences in skin morphology among B. indicus, B. taurus and their crossbreds, with these differences being more or less related to the genetic fraction of HF. This may imply that capability for cutaneous evaporative heat loss and tolerance to heat in crossbred cattle could be related to skin morphology.

Evaporative cooling and cutaneous surface temperature of Holstein cows in tropical conditions

The effects of skin temperature (T S) on the rate of heat loss by cutaneous evaporation (E S) in Holstein cows chronically exposed to sun, considering hair coat colour were studied. Sixteen purebred cows were measured for E S and T S at 01:00 p.m. after 6 hours of exposure to sun, on three body regions (flank, neck and gluteus) and considering dark and white spots separately. Sweating rate (S) and E S were measured by means of a ventilated capsule. Black skin areas presented mean S (138.9 ± 8.5 gm-2 h-1), E S (93.3 ± 5.7 Wm-2), and T S (33.1 ± 0.2°C) higher than those in the white areas (109.5 ± 9.7 gm-2h-1), 73.6 ± 6.5 Wm-2 and 32.6 ± 0.2°C, respectively). There is an exponential relationship among cutaneous temperature and cutaneous evaporation, which can be represented by the equation: E S = 31.5 + exp{(T S - 27.9)/2.19115}, with coefficient of determination r² = 0.68. Cutaneous evaporative heat loss remains almost constant around 48 Wm-2 until T S reaches nearly 31°C.

The effect of coat clipping on thermoregulation during intense exercise in trotters.

The aim of this study was to study the physiological, especially thermoregulatory, responses during intense exercise in the clipped horse compared to the horse with winter coat. Six Standardbred trotters were studied before and after clipping. They performed an inclined incremental high intensity treadmill exercise test and were monitored during recovery. The clipped horse differed significantly (ANOVA) during exercise as compare to coated: less increase in central venous blood temperature, higher skin surface temperature, greater difference skin to ambient temperature and higher rate of nonevaporative heat loss. The clipped horse had significantly lower total cutaneous evaporative heat loss from walk to end of peak exercise and a shorter time for recovery for the respiratory rate using a paired t test. The clipped horse showed a tendency (P = 0.059) to decreased oxygen uptake during the stepwise increase in workload. We concluded that the clipped horse experienced less strain on the thermoregulatory system due to an enhanced heat loss. Some clipped horses in the study showed a more efficient power output; future studies with emphasis on respiration and oxygen demand are needed to explain this.

Thermoregulation by Kangaroos from Mesic and Arid Habitats: Influence of Temperature on Routes of Heat Loss in Eastern Grey Kangaroos (Macropus giganteus) and Red Kangaroos (Macropus rufus)

We examined thermoregulation in red kangaroos (Macropus rufus) from deserts and in eastern grey kangaroos (Macropus giganteus) from mesic forests/woodlands. Desert kangaroos have complex evaporative heat loss mechanisms, but the relative importance of these mechanisms is unclear. Little is known of the abilities of grey kangaroos. Our detailed study of these kangaroos' thermoregulatory responses at air temperatures (T(a)) from -5 degrees to 45 degrees C showed that, while some differences occur, their abilities are fundamentally similar. Both species show the basic marsupial characteristics of relatively low basal metabolism and body temperature (T(b)). Within the thermoneutral zone, T(b) was 36.3 degrees + or - 0.1 degrees C (X + or - SE) in both species, and except for a small rise at T(a) 45 degrees C, T(b) was stable over a wide range of T(a). Metabolic heat production was 25% higher in red kangaroos at T(a) -5 degrees C. At the highest T(a) (45 degrees C), both species relied on evaporative heat loss (EHL) to maintain T(b); both panting and licking were used. The eastern grey kangaroo utilised panting (76% of EHL) as the principal mode of EHL, and while this was so for red kangaroos, cutaneous evaporative heat loss (CEHL) was significant (40% of EHL). CEHL appeared to be mainly licking, as evidenced from surface temperatures. Both species utilised peripheral vascular adjustments to control heat flow, as indicated by changes in dry conductance (C(dry)). At lower temperatures, C(dry) was minimal, but it increased significantly at T(a) just below T(b) (33 degrees C); in these conditions, the C(dry) of red kangaroos was significantly higher than that of eastern grey kangaroos, indicating a greater reliance on dry heat loss. Under conditions where heat flows into the body from the environment (T(a) 45 degrees C), there was peripheral vasoconstriction to reduce this inflow; C(dry) decreased significantly from the values seen at 33 degrees C in both kangaroos. The results indicated that, while both species have excellent thermoregulatory abilities, the desert red kangaroos may cope better with more extreme temperatures, given that they respond to T(a) 45 degrees C with lower respiratory evaporation than do the eastern grey kangaroos.

Rate and composition of sweat fluid losses are unaltered by hypohydration during prolonged exercise in horses.

Rate and ionic composition of sweat fluid losses and partitioning of evaporative heat loss into respiratory and cutaneous components were determined in six horses during three 15-km phases of exercise at approximately 40% of maximal O2 uptake. Pattern of change in sweat rate (SR) and composition was similar during each phase. SR increased rapidly for the first 20 min of exercise but remained at approximately 24-28 ml . m-2 . min-1 during the remainder of each phase. Similarly, the concentrations of Na and Cl in sweat increased until 30 min of exercise but were unchanged thereafter. Sweat osmolality and concentrations of Na and Cl were positively correlated with SR. Sweat K concentration decreased during exercise but was not correlated with SR. Fluid losses were 33.8 +/- 1.5 liters, resulting in decreases of approximately 21% in plasma volume and approximately 11% in total body water. The approximately 6% hypohydration was not associated with an alteration in SR, sweat composition, or heat storage. Respiratory and cutaneous evaporative heat loss represented approximately 23 and 70%, respectively, of the total heat dissipated, and the partitioning of heat loss was similar in each exercise phase. We conclude that SR and the relative proportions of respiratory and cutaneous evaporative heat loss are unchanged in horses during prolonged low-intensity exercise despite moderate hypohydration.

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Climatic energy demand of horses

SummaryThe objective of this study was to determine the climatic energy demand i.e. the non‐evaporative heat loss expressed in watts per square metre (W/m2) of horses at low temperatures. Five horses were used; 4 Standardbred trotters and 1 Shetland pony stallion. The horses were fed for maintenance and light work and housed in a warm environment (15–20°C). Measurements were made in a climate chamber at 6 different temperatures; ‐3, 6, 15, 20, 30 and 37°C. Each horse was in the climate chamber for 1.5 h on each occasion. The measuring period was 1 h. A hygrometric tent inside the climate chamber was used to measure evaporative heat loss. Ambient air temperature, radiant temperature, deep body temperature, skin and coat temperatures were measured and, together with cutaneous evaporative heat loss, used to calculate the non‐evaporative heat loss. The lower critical temperature (LCT) was estimated for each horse in the study. The average LCT of horses acclimatised to an indoor temperature of 15–29°C was 18.2°C. At LCT the average total heat loss was 127 W/m2. The corresponding partitioned heat loss was 96 W/m2 non‐evaporative and 31 W/m2 evaporative. The results show an average maximal tissue thermal resistance of 0.076 K·m2/W and an average thermal resistance of the coat of 0.087 K·m2/W. The climatic energy demand for these horses was 3 W/m2·°C for temperatures below LCT in dry and calm conditions. For a 500 kg horse this additional energy requirement could be met by an extra 0.15 kg hay/°C below LCT. Smaller and lighter weight horses need relatively more feed in cold conditions.

A Comparative Study of Heating Rates in Arboreal and Nonarboreal Frogs

Heating rates and time constants of heating were determined for similarly sized green tree frogs, Hyla cinerea, and southern leopard frogs, Rana sphenocephala exposed to step changes in ambient temperature from 15 to 30?C. Whereas the initial body temperatures were not significantly different (15?C), equilibration body temperatures were significantly higher in H. cinerea (26.6?C) than in R. sphenocephala (18.1?C). Rates of temperature change were 2.5 x higher in H. cinerea and are explained by the presence of reduced cutaneous evaporative heat loss in this species. The thermal time constant is inappropriate for interspecific comparisons of heating in anurans. lo , ol. 23, No. 2, pp. 141-145, 1989 ciet for the Study of Amphibians and Reptiles of eating Rates in a oreal Frogs During the nearly twenty years since reduced cutaneous evaporative water loss (CWL) was first reported in an arboreal frog (Loveridge, 1970), some degree of waterproofing has been found to be present among species belonging to at least nine tree frog genera (see Wygoda, 1988b). Because anuran hydroand thermoregulation are closely linked (Tracy, 1976; Bundy and Tracy, 1977; Beuchet et al., 1984), profound differences in thermoregulatory strategies are expected to be present between these frogs and non-waterproof frogs. However, little is known of the thermal consequences of CWL reduction because, with few exceptions (McClanahan et al., 1978; Wygoda, 1984, 1988a, b; Shoemaker et al., 1987), simultaneous water loss and body temperature measurements have not been performed. It is known that body temperatures (Tbs) of waterproof arboreal frogs approximate air temperature (Ta) up to around 40?C (Shoemaker et al., 1987), but remain constant when Ta is further increased (McClanahan et al., 1978; Shoemaker et al., 1987). TbS of non-thermally stressed moderately waterproof arboreal frogs are intermediate between Ta and the Tb of nonwaterproof frogs (Wygoda, 1984) and are less coupled to relative humidity (RH) changes than are those of non-waterproof frogs (Wygoda, 1988b). In addition to providing elevated Tbs, rel., 1987), simultaneous water loss and body e perature measurements have not b e perormed. It is known that body temperatures (Tbs) f waterproof arbo eal frogs approximate air e perature (Ta) up to around 40?C (Shoemaker t al., 1987), but remain constant whe Ta is 141 This content downloaded from 40.77.167.54 on Thu, 06 Oct 2016 04:20:27 UTC All use subject to http://about.jstor.org/terms

Post-Effect of Ammonia on Energetics of Laying Hens at High Temperatures

ABSTRACT WHITE Leghorn layers were monitored for heat loss, feed intake, egg production and respiratory rate at various environmental temperatures (TJ after first being exposed to aerial ammonia (NH3). The initial exposure was to 10 or 60 ppm NH3 at a T, of 25 C for 30 days to simulate a winter environmental condition in a poultry facility. Hens were then allowed to recover in an environment of 5 ppm of NH3 at a T^ of 22 C for seven days to simulate a spring environmental condition. Birds were then placed individually in a partitional calorimeter free of NH3 at 25, 29, 33, or 37 C for 24 h to simulate initial summer environmental conditions. There were no statistical differences (P>0.05) between the two groups of NH3-treated hens for sensible or latent heat losses, apparent respiratory efficiency of latent heat loss, egg production, or feed intake. From these resutls, it is hypothesized that interplay between cutaneous evaporative heat loss and respiratory evaporative heat loss may play a more important physiological role than previously thought in maintaining homeothermy of the bird at high environmental temperatures. This physiological reponse could thus provide an energetics compensation for lung damage caused by aerial ammonia.

Quantitative aspects of preoptic thermosensitivity in the conscious ox.

An attempt has been made to study the quantitative relationship between the temperature of the anterior hypothalamic/preoptic (AH/PO) region and heat balance in the conscious ox (Bos taurus) at a thermoneutral air temperature of 20 degrees C. Heat balance was measured by combined gradient-layer and open-circuit calorimetry and AH/PO temperature was controlled using a water-perfused thermode. Continuous warming or cooling of the AH/PO region caused a transient heat imbalance which shifted core temperature to a new stable level dependent upon the level of stimulation. The heat balance responses to continuous AH/PO warming included peripheral vasodilation and increased respiratory and cutaneous evaporative heat loss; those to AH/PO cooling consisted mainly of decreased heat loss. Heat production was largely unaffected by both AH/PO warming and cooling. The heat balance responses developed only slowly, reaching a peak up to 50 min after the start of stimulation and taking several hours to complete. The change to stability in core temperature during continuous AH/PO stimulation and the additional heat loss prior to that stability were the most sensitive indicators of response of all the variables measured. A significant response was observed in these parameters even at the smallest stimulus level (less than 0.33 degrees C) and correlation of response with stimulus level was precise with a zero threshold for response. This suggests a continuity of operation of the AH/PO mechanism about zero. Several responses showed a curved relationship between slope of response and stimulus level, such that the increment in response per unit increase in stimulus level became greater as stimulus level increased. The results suggest a two-tier form of thermoregulation in the ox with AH/PO sensitivity to warming greater than its sensitivity to cooling. It appears also that AH/PO temperature is at least as dominant in the thermoregulatory mechanisms in the ox as it is in smaller animals.

Evaporative heat loss in the California Sea Lion and Harbor Seal

1. 1. Total evaporative heat loss was measured in four California Sea Lions and one Harbor Seal at air temperatures between 13 and 30°C. The total heat loss was partitioned into respiratory and cutaneous components. 2. 2. Thermal polypnea was not observed to occur in any of the animals and respiratory evaporative heat loss was estimated to represent less than 3 per cent of the heat production when the animals were hyperthermic in a hot environment (31°C). 3. 3. Active sweating was noted on the bare skin of the flippers of the sea lions but not on the haired surface of the torso. The total cutaneous evaporative heat loss accounted for approximately 16 per cent of the heat produced by metabolism, in a hot environment. 4. 4. It was concluded that evaporative heat loss mechanisms were relatively ineffective in California Sea Lions and in the Harbor Seal also.