Thermoregulation in ratites: a review

2008 ◽  
Vol 48 (10) ◽  
pp. 1293 ◽  
Author(s):  
Shane K. Maloney
Keyword(s):  
Tidal Volume ◽  
Water Loss ◽  
Production Systems ◽  
Brain Temperature ◽  
Respiratory Alkalosis ◽  
Evaporative Water ◽  
Hypothalamic Temperature ◽  
Blood Temperature ◽  
Arterial Blood ◽  
Free Ranging

Laboratory and free-ranging studies on the emu, ostrich and kiwi show ratites to be competent homeotherms. While body temperature and basal metabolic rate are lower in ratites than other birds, all of the thermoregulatory adaptations present in other birds are well established in ratites. The thermoneutral zone has been established for the emu and kiwi, and extends to 10°C. Below that zone, homeothermy is achieved via the efficient use of insulation and elevated metabolic heat production. In the heat, emus and ostriches increase respiratory evaporative water loss and use some cutaneous water loss. Respiratory alkalosis is avoided by reducing tidal volume. In severe heat, tidal volume increases, but the emu becomes hypoxic and hypocapnic, probably by altering blood flow to the parabronchi, resulting in ventilation/perfusion inhomogeneities. Ostriches are capable of uncoupling brain temperature from arterial blood temperature, a phenomenon termed selective brain cooling. This mechanism may modulate evaporative effector responses by manipulating hypothalamic temperature, as in mammals. The implications of thermal physiology for ratite production systems include elevated metabolic costs for homeothermy at low ambient temperature. However, the emu and ostrich are well adapted to high environmental temperatures.

Blood and brain temperatures of free-ranging black wildebeest in their natural environment

1994 ◽  
Vol 267 (6) ◽  
pp. R1528-R1536 ◽  
Author(s):  
C. Jessen ◽  
H. P. Laburn ◽  
M. H. Knight ◽  
G. Kuhnen ◽  
K. Goelst ◽  
...  
Keyword(s):  
Brain Temperature ◽  
Natural Habitat ◽  
Radiant Heat ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood ◽  
Data Loggers ◽  
Free Ranging ◽  
Arterial Blood Temperature

Using miniature data loggers, we measured the temperatures of carotid blood and brain in four wildebeest (Connochaetes gnou) every 2 min for 3 wk and every 5 min, in two of the animals, for a further 6 wk. The animals ranged freely in their natural habitat, in which there was no shelter. They were subject to intense radiant heat (maximum approximately 1,000 W/m2) during the day. Arterial blood temperature showed a circadian rhythm with low amplitude (< 1 degree C) and peaked in early evening. Brain temperature was usually within 0.2 degrees C of arterial blood temperature. Above a threshold between 38.8 and 39.2 degrees C, brain temperature tended to plateau so that the animals exhibited selective brain cooling. However, selective brain cooling sometimes was absent even when blood temperature was high and present when it was low. During helicopter chases, selective brain cooling was absent, even though brain temperature was near 42 degrees C. We believe that selective brain cooling is controlled by brain temperature but is modulated by sympathetic nervous system status. In particular, selective brain cooling may be abolished by high sympathetic activity even at high brain temperatures.

Rectal temperature measurement results in artifactual evidence of selective brain cooling

2001 ◽  
Vol 281 (1) ◽  
pp. R108-R114 ◽  
Author(s):  
Shane K. Maloney ◽  
Andrea Fuller ◽  
Graham Mitchell ◽  
Duncan Mitchell
Keyword(s):  
Rectal Temperature ◽  
Brain Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood ◽  
The Status ◽  
Conscious Sheep ◽  
Surrogate Measures ◽  
Arterial Blood Temperature

Selective brain cooling (SBC) is defined as a brain temperature cooler than the temperature of arterial blood from the trunk. Surrogate measures of arterial blood temperature have been used in many published studies on SBC. The use of a surrogate for arterial blood temperature has the potential to confound proper identification of SBC. We have measured brain, carotid blood, and rectal temperatures in conscious sheep exposed to 40, 22, and 5°C. Rectal temperature was consistently higher than arterial blood temperature. Brain temperature was consistently cooler than rectal temperature during all exposures. Brain temperature only fell below carotid blood temperature during the final few hours of 40°C exposure and not at all during the 5°C exposure. Consequently, using rectal temperature as a surrogate for arterial blood temperature does not provide a reliable indication of the status of the SBC effector. We also show that rapid suppression of SBC can result if the animals are disturbed.

Dehydration increases the magnitude of selective brain cooling independently of core temperature in sheep

2007 ◽  
Vol 293 (1) ◽  
pp. R438-R446 ◽  
Author(s):  
Andrea Fuller ◽  
Leith C. R. Meyer ◽  
Duncan Mitchell ◽  
Shane K. Maloney
Keyword(s):  
Drinking Water ◽  
Brain Temperature ◽  
Heat Exposure ◽  
Plasma Osmolality ◽  
Threshold Temperature ◽  
Evaporative Heat Loss ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Blood Temperature ◽  
Arterial Blood

By cooling the hypothalamus during hyperthermia, selective brain cooling reduces the drive on evaporative heat loss effectors, in so doing saving body water. To investigate whether selective brain cooling was increased in dehydrated sheep, we measured brain and carotid arterial blood temperatures at 5-min intervals in nine female Dorper sheep (41 ± 3 kg, means ± SD). The animals, housed in a climatic chamber at 23°C, were exposed for nine days to a cyclic protocol with daytime heat (40°C for 6 h). Drinking water was removed on the 3rd day and returned 5 days later. After 4 days of water deprivation, sheep had lost 16 ± 4% of body mass, and plasma osmolality had increased from 290 ± 8 to 323 ± 9 mmol/kg ( P < 0.0001). Although carotid blood temperature increased during heat exposure to similar levels during euhydration and dehydration, selective brain cooling was significantly greater in dehydration (0.38 ± 0.18°C) than in euhydration (−0.05 ± 0.14°C, P = 0.0008). The threshold temperature for selective brain cooling was not significantly different during euhydration (39.27°C) and dehydration (39.14°C, P = 0.62). However, the mean slope of lines of regression of brain temperature on carotid blood temperature above the threshold was significantly lower in dehydrated animals (0.40 ± 0.31) than in euhydrated animals (0.87 ± 0.11, P = 0.003). Return of drinking water at 39°C led to rapid cessation of selective brain cooling, and brain temperature exceeded carotid blood temperature throughout heat exposure on the following day. We conclude that for any given carotid blood temperature, dehydrated sheep exposed to heat exhibit selective brain cooling up to threefold greater than that when euhydrated.

Respiratory Function in Exercising Fowl Following Occlusion of the Thoracic Am Sacs

1989 ◽  
Vol 145 (1) ◽  
pp. 227-237 ◽  
Author(s):  
JOHN H. BRACKENBURY ◽  
CARL DARBY ◽  
MAHMOUD S. EL-SAYED
Keyword(s):  
Oxygen Consumption ◽  
Water Loss ◽  
Respiratory Function ◽  
Treadmill Exercise ◽  
Minute Ventilation ◽  
Resting Metabolic Rate ◽  
Differential Distribution ◽  
Evaporative Water ◽  
Arterial Blood ◽  
Air Sacs

Oxygen consumption, respiratory evaporative water loss, respiratory rate and gas tensions in the clavicular and abdominal air sacs and in arterial blood were monitored after occluding either the cranial thoracic air sac only (CRT group) or the cranial and caudal thoracic air sacs together (CRT-CT group). Respiratory water loss was used to estimate minute ventilation. Both experimental groups were able to maintain control levels of ventilation at rest and during treadmill exercise at approximately three times the resting metabolic rate. The CRT group regulated blood and intrapulmonary PCOCO2 and POO2 normally, but there was a slight hypoxaemia/hypercapnaemia in the CRT-CT group, apparently as a result of parabronchial hypoventilation. The differential distribution of gas tensions between the cranial and caudal groups of air sacs was the same in control and experimental birds, suggesting that a normal intrapulmonary airflow pattern was preserved in the absence of the thoracic air sacs. The findings are discussed in the light of current models of the control of intrapulmonary airflow in birds.

Ventilatory and Circulatory Responses to Hyperthermia in the Mute Swan (CYGNUS OLOR)

1980 ◽  
Vol 88 (1) ◽  
pp. 195-204
Author(s):  
C. BECH ◽  
K. JOHANSEN
Keyword(s):  
Tidal Volume ◽  
Peripheral Resistance ◽  
Respiratory Alkalosis ◽  
Deep Body Temperature ◽  
Cygnus Olor ◽  
Arterial Blood ◽  
Arterial Ph ◽  
End Tidal ◽  
Mute Swans ◽  
Hypocapnic Alkalosis

Ventilatory parameters of mute swans were measured at thermoneutral conditions and during heat stress. Deep body temperature increased from 39·5 to 41·1 °C. Breathing frequency increased 29 times, compared to the thermoneutral condition. Tidal volume decreased to 18 % of the pre-panting value, and the total ventilatory volume increased by 5·4 times. End-tidal PCOCO2 and POO2 values decreased and increased, respectively. The swans developed a slight respiratory alkalosis; arterial Pcoco2 decreased from an average of 27·1 to 25·7 mmHg and arterial pH increased from 7·501 to 7·559. Cardiac output, heart rate and stroke volume were 106%, 154%, and 70%, respectively, of the values at thermoneutrality. Mean arterial blood pressure and total peripheral resistance were slightly reduced. It is concluded that the increased ventilation during panting mainly constitutes dead space ventilation resulting from the great reduction in tidal volume. Parabronchial ventilation remains nearly unchanged, resulting in only a slight hypocapnic alkalosis.

Activity, blood temperature and brain temperature of free-ranging springbok

1997 ◽  
Vol 167 (5) ◽  
pp. 335-343 ◽  
Author(s):  
Duncan Mitchell ◽  
Shane K. Maloney ◽  
Helen P. Laburn ◽  
Michael H. Knight ◽  
Gernot Kuhnen ◽  
...  
Keyword(s):  
Brain Temperature ◽  
Blood Temperature ◽  
Free Ranging

The contribution of carotid rete variability to brain temperature variability in sheep in a thermoneutral environment

2007 ◽  
Vol 292 (3) ◽  
pp. R1298-R1305 ◽  
Author(s):  
Shane K. Maloney ◽  
Duncan Mitchell ◽  
Dominique Blache
Keyword(s):  
Blood Flow ◽  
Temperature Difference ◽  
Heat Production ◽  
Brain Temperature ◽  
Brain Blood Flow ◽  
Tight Coupling ◽  
Hypothalamic Temperature ◽  
Arterial Blood ◽  
Carotid Arterial ◽  
The Brain

The degree of variability in the temperature difference between the brain and carotid arterial blood is greater than expected from the presumed tight coupling between brain heat production and brain blood flow. In animals with a carotid rete, some of that variability arises in the rete. Using thermometric data loggers in five sheep, we have measured the temperature of arterial blood before it enters the carotid rete and after it has perfused the carotid rete, as well as hypothalamic temperature, every 2 min for between 6 and 12 days. The sheep were conscious, unrestrained, and maintained at an ambient temperature of 20–22°C. On average, carotid arterial blood and brain temperatures were the same, with a decrease in blood temperature of 0.35°C across the rete and then an increase in temperature of the same magnitude between blood leaving the rete and the brain. Rete cooling of arterial blood took place at temperatures below the threshold for selective brain cooling. All of the variability in the temperature difference between carotid artery and brain was attributable statistically to variability in the temperature difference across the rete. The temperature difference between arterial blood leaving the rete and the brain varied from −0.1 to 0.9°C. Some of this variability was related to a thermal inertia of the brain, but the majority we attribute to instability in the relationship between brain blood flow and brain heat production.

Metabolism, Respiration and Evaporative Water Loss in the Australian Hopping-Mouse Notomys Alexis (Rodentia: Muridae).

1979 ◽  
Vol 27 (2) ◽  
pp. 195 ◽  
Author(s):  
PC Withers ◽  
AK Lee ◽  
RW Martin
Keyword(s):  
Oxygen Consumption ◽  
Body Temperature ◽  
Tidal Volume ◽  
Water Loss ◽  
Minute Volume ◽  
Evaporative Water Loss ◽  
Moist Air ◽  
Evaporative Water ◽  
Ambient Temperatures ◽  
Dry Air

Resting oxygen consumption and total evaporative water loss were determined for N. alexis at ambient temperatures of 20, 28 and 33 deg C in dry air. The minimum rate of oxygen consumption was 0.61 ml min-1 at 33 deg C, and minimum total evaporative water loss was 4.75% body mass day-1 at 28 deg C. Respiration frequency, tidal volume and respiratory minute volume were determined for N. alexis at ambient temperatures of 20, 28 and 33 deg C in air of low or high relative humidity. Minimum values were obtained at 28 deg C and low RH for respiratory minute volume and tidal volume, and at 28 deg C and high RH for respiratory frequency. Expired air temperature of N. alexis at these temperatures was lower than or similar to ambient for mice in air of low RH, but was higher than or similar to ambient at high RH. Respiratory evaporative water loss, calculated from the previous data, was greatest for mice in dry air at 33 deg C, and least in moist air at 33 deg C. Cutaneous evaporative water loss made up about 40-60% of the total evaporative water loss for mice in dry air. The rates of total evaporative water loss were clearly reflected in the manner of body temperature regulation at high ambient temperatures. Hopping-mice in moist air at 28 and 33 deg C became hyperthermic, whereas mice in dry air showed only slight increases in body temperature. The significance of these data to hopping-mice in the field was discussed.

scholarly journals Guttural pouches, brain temperature and exercise in horses

2006 ◽  
Vol 2 (3) ◽  
pp. 475-477 ◽  
Author(s):  
Graham Mitchell ◽  
Andrea Fuller ◽  
Shane K Maloney ◽  
Nicola Rump ◽  
Duncan Mitchell
Keyword(s):  
Brain Temperature ◽  
Brain Cooling ◽  
Selective Brain Cooling ◽  
Free Living ◽  
Heat Injury ◽  
Blood Temperature ◽  
Arterial Blood ◽  
Exchange Function ◽  
The Brain ◽  
Arterial Blood Temperature

Selective brain cooling (SBC) is defined as the lowering of brain temperature below arterial blood temperature. Artiodactyls employ a carotid rete, an anatomical heat exchanger, to cool arterial blood shortly before it enters the brain. The survival advantage of this anatomy traditionally is believed to be a protection of brain tissue from heat injury, especially during exercise. Perissodactyls such as horses do not possess a carotid rete, and it has been proposed that their guttural pouches serve the heat-exchange function of the carotid rete by cooling the blood that traverses them, thus protecting the brain from heat injury. We have tested this proposal by measuring brain and carotid artery temperature simultaneously in free-living horses. We found that despite evidence of cranial cooling, brain temperature increased by about 2.5 °C during exercise, and consistently exceeded carotid temperature by 0.2–0.5 °C. We conclude that cerebral blood flow removes heat from the brain by convection, but since SBC does not occur in horses, the guttural pouches are not surrogate carotid retes.

Shell Resistance and Evaporative Water Loss from Bird Eggs: Effects of Wind Speed and Egg Size

1981 ◽  
Vol 54 (2) ◽  
pp. 195-202 ◽  
Author(s):  
James R. Spotila ◽  
Christina J. Weinheimer ◽  
Charles V. Paganelli
Keyword(s):  
Wind Speed ◽  
Water Loss ◽  
Egg Size ◽  
Evaporative Water Loss ◽  
Evaporative Water ◽  
Bird Eggs
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