Jacob Marder

Cutaneous water evaporation—I. Its significance in heat-stressed birds

In a comparative study on avian cutaneous evaporation, two species of Phasianidae, Japanese quail Coturnix coturnix japonica and chukar partridge Alectoris chukar, and three species of Columbidae, palm dove Streptopelia senegalensis, collared turtle dove Streptopelia decaocto and rock pigeon Columbia livia, were investigated. The skin resistance to vapor diffusion (rs) and cutaneous water loss (CWL) were studied in these birds exposed to air temperatures (Ta) between 20 and 52 degrees C. The skin resistance was measured with Lambda instrument diffusive resistance meter. Skin resistance within the thermo-neutral zone varied between a minimum of 62 sec/cm in the palm dove exposed to 20 degrees C and a maximum of 309.1 sec/cm in the partridge exposed to 36 degrees C. The CWL values were 2.5 mg H2O/cm2.hr and 0.51 mg H2O/cm2.hr respectively. Maximum CWL of the quail and partridge was 1.9-2.1 mg H2O/cm2.hr, equivalent to a cooling capacity of about 17% of metabolic heat production at 45 degrees C Ta. In the palm dove, collared dove and pigeon CWL reached 6.8, 13.1 and 20.9 mg H2O/cm2.hr and rs values reached 31.2, 16.2 and 9.4 sec/cm respectively. The cooling capacity amounted to 51.5, 86.1 and 96.5% of metabolic heat during heat stress (52 degrees C). The significance of skin evaporation in body temperature regulation of heat-stressed birds is discussed.

Heat balance of acclimated pigeons (Columba livia) exposed to temperatures up to 60°c ta

Abstract 1. 1. Hand-reared acclimated (Acc) and nonacclimated (NAcc) rock pigeons Columba livia were exposed to ambient temperatures (Ta) of 30–65°C and low relative humidities (RH) of 5–35%. 2. 2. Resting heat production of 3.6 ± 0.7 cal g −1 hr−1 (31.7 W/m2) and 4.9 ± 0.8 cal g −1 hr −1 (43.0 W/m2) were measured in Ace and NAcc pigeons, respectively. 3. 3. The total evaporative water loss (EWL) was significantly lower (P 4. 4. At 60°C Ta, acclimated pigeons dissipated 304% of heat production as latent heat. In Acc birds body temperature was regulated between 41.2 and 42.0°C within the thermoneutral zone (TNZ) (30–60°C). 5. 5. In NAcc pigeons the TNZ extends only between 30 and 42°C Ta. When Ta was increased from 35–45°C hyperthermia developed at 0.11°C/1°C increase in Ta. 6. 6. The heat acclimated pigeon effectively uses cutaneous evaporation instead of panting and gular fluttering for dissipation of both metabolic heat and ambient heat influx. 7. 7. The significance of the skin and the feather coat in the adaptation of birds to life in the hot deserts is discussed.

Serum electrolyte and enzyme responses to heat stress and dehydration in the fowl (Gallus domesticus)

1. Serum electrolytes, enzymes and various metabolites were determined in the hyperthermic and dehydrated fowl. 2. In normally-hydrated fowls, heat stress did not significantly affect blood constituents. 3. Water deprivation for 48 hr (dehydration) significantly (p less than 0.05) increased Na+, osmolality, SGPT and T3-retention. 4. During hyperthermic dehydration, Na+, Cl-, osmolality (p less than 0.01), BUN, glucose, T3-retention (p less than 0.02) and uric acid (p less than 0.001) significantly increased. 5. The present findings are consistent with the suggestion that changes in Na+/Ca2+ ratio might raise the hypothalamic thermoregulatory set-point and support our previous findings that acclimated fowls could efficiently regulate body temperature and acid-base status while avoiding extreme metabolic and enzymatic changes during heat exposure and dehydration.

Comparative thermoregulation of four breeds of fowls (Callus domesticus), exposed to a gradual increase of ambient temperatures

Abstract 1. I. Fowls of four breeds, Sinai, Leghorn, Sinai × Leghorn and Leghorn × Sinai, were gradually exposed to increasing ambient temperatures. 2. 2. Body temperature (Tb) increased at the rate of 0.121 C for every 1 C increase of ambient temperature (Ta) in the range of 25–45 C Ta. 3. 3. Heart rate (HR) was regulated at a stable, lower than normothermic level. 4. 4. Respiration rates (ƒ) increased 17 fold over the normal rates, contributing to a 6.64 fold increase in evaporative water loss (EWL), and this dissipated 170% of the metabolic heat production at 45 C Ta. 5. 5. The fowls maintained a stable oxygen consumption up to 42 C and at 45 C it increased by only 15% over the normothermic level. 6. 6. All breeds efficiently regulated their body temperature below ambient temperature at 45 C. However, the desert Sinai breed was characterized by 10% lower than predicted SMR and by a shallow high frequency panting compared to the Leghorn.

The effect of heat exposure on blood chemistry of the hyperthermic rabbit.

1. Two hours of exposure to heat stress, resulted in hyperthermia in rabbits (Oryctolagus cuniculus). 2. This was accompanied by a severe hypocapnia, partly compensated for by a significant decrease in bicarbonate (HCO3-) concentration. 3. The severest hyperthermia (Tb = 43.5 degrees) was followed by a sharp decreased in both PaCO2 (to 20.2 torr) and HCO3- (to 9.2 mM/l), resulting in extreme metabolic acidosis (pH = 7.290). 4. The significant increase in serum osmolality (27%) is interpreted by the cumulative effect of increased electrolyte and metabolite concentrations. 5. The elevation in blood BUN, creatinine, globulin and GOT levels point to a possible damage to muscle cells by hypothermia. 6. The stable cholesterol and alkaline phosphatase levels, suggest that liver tissue was not damaged. 7. The dramatic increase in glucose from 103.8 to 348.8 mg%, and the significant increase (from 22.0 to 39.9 mg%) in BUN, suggest a possible disability of the cells to metabolize carbohydrates, accompanied by a progressive proteolysis as an alternative process for energy production. 8. The data suggest that the emergence of muscle cell damage, severe hyperglycemia and acidosis under heat stress, precedes and amplifies the deteriorating effects of high Tb in heat stressed rabbits, which often lead to mortality.

Adaptive changes in the epidermal structure of the heat‐acclimated rock pigeon (Columba livia): A comparative electron microscopy study

The purpose of this study was to find out whether the microstructure of the highly permeable skin of heat‐acclimated pigeons allowing increased evaporative cooling differs from the skin of pigeons in the non‐acclimated or cold‐acclimated state. In addition, the correlation between epidermal morphology and cutaneous water evaporation in heat‐acclimated pigeons was elucidated. The epidermis of heat‐acclimated pigeons differs in several respects from the epidermis of non‐acclimated or cold‐acclimated birds. Both the dorsal and the abdominal skin include modified areas, characterized by increased vascularization, epidermis with greater thickness, and changes in intracellular structures. Greater thickness results from hypertrophy of epidermal cells possibly due to greater fluid content of the sebokeratinocytes in the germinative layers. The stratum corneum includes corneocytes with thickened cornified envelopes and contains greater mass of keratin‐complex material compared to non‐acclimated and cold‐acclimated pigeons. The extracellular space between the compactly piled corneocytes contains amorphous lipoid material. The multigranular bodies lack compact organization of lipid bilayers. The transitional layer in the heat‐acclimated pigeon displays atypical keratohyalin granules, which are multilateral and dendritic in shape. It is concluded that the dorsal and abdominal skin of heat‐acclimated pigeons contains areas that differ in structure from their counterparts in non‐acclimated and cold‐acclimated pigeons. The structural characteristics of these modified patches suggest a high rate of cutaneous evaporation and decreased skin resistance to transepidermal diffusion of water vapor. Thus, the skin of a heat‐acclimated pigeon responds to the thermoregulatory requirements for increased cutaneous water evaporation by structural changes. J. Morphol. 235:17–29, 1998.

Cutaneous water evaporation—II. Survival of birds under extreme thermal stress

Two birds, the pigeon (Columba livia) and the partridge (Alectoris chukar), differing in their habits and flight ability were compared with regard to their ability to survive extreme high air temperatures (Tas). During 270 min survival tests birds were exposed to Tas between 45 and 60 degrees C and low relative humidities. The pigeon was observed to be unique in its ability to survive 270 min of exposure to 60 degrees C while regulating Tb at 43.8 degrees C. The partridge could not survive 270 min of exposure at Tas exceeding 48 degrees C. The pigeons were found to be exceptional in their capacity for cutaneous evaporation. Values as high as 20.9 mg H2O/cm-2/hr were measured at 52 degrees C Ta compared to 2.4 mg H2O/cm-2/hr in the partridge. Total evaporation of the pigeon exposed to 56 degrees C Ta was about 20% higher than that in the partridge. Maximum evaporation of the pigeon exposed to 60 degrees C Ta was 34.4 mg H2O/g/hr. The significance of cutaneous water loss for survival during extreme high Tas is discussed. It is concluded that birds as a class may be divided into two groups with regard to their physiological capacity to withstand heat stress: (1) the majority of studied species employ regular physiological mechanisms and are limited in their cooling capacity to withstand ambient temperatures 48 degrees C; (2) a few avian species, which may be of wide ecological distribution, are equipped with major physiological preadaptations to severe heat stress.

Acid base status in unanesthetized, unrestrained guinea pigs

Acid-base status of arterial blood was measured in chronically cannulated, unanesthetized, unrestrained guinea pigs. Normal values were: pH=7.444±0.032,PaCO2=35.7±4.4; HCO3−=24.4±2.8; BE=+0.4±2.1 (n=69) andPaO2=91.9±7.3 (n=25) (Values are mean±S.D.).Induction of light anesthesia with thiopentone caused a respiratory depression (decrease inPaO2) accompanied by respiratory acidosis (increase inPaCO2 and decrease in pH) and a development of slight metabolic acidosis (decrease in base excess and standard bicarbonate). Acid base parameters of guinea pigs are compared to those obtained from rats under identical experimental conditions.

The acid base balance of Abdim's stork (Sphenorhynchus abdimii) during thermal panting.

Abstract 1. 1. The effect of long-term (8–10 hr) exposure to heat stress (40–45°C) on acid base balance of Abdims stork (Sphenorhynchus abdimii) was investigated. 2. 2. Body temperature reached a maximum of 41·15°C (at 45°C Ta), as compared to about 40·0°C at 24–30°C Ta. 3. 3. Normal respiratory rates (10 c/min) increased to 100–112 c/min at ambients of 40, 42 and 45°C. 4. 4. Normal arterial pH, PCO2 and [HCO3−]were 7·564, 27·9 and 25·09, respectively. After 10 hr of intensive panting, values were 7·571, 25·5 and 23·09. 5. 5. These results are discussed in relation to a possible shunt mechanism, effective in preventing washout of gas-exchange surfaces in a flying birds lungs.

Acid-base regulation during thermal panting in the fowl (Gallus domesticus): comparison between breeds.

1. The effects of high ambient temperatures on blood acid base status were studied in four breeds of fowl. 2. All breeds efficiently regulated body temperature below ambient temperature at 45 degrees C (Tb = 38.521 + 0.110Ta, at 25-45 degrees C). 3. A slight hypocapnia was partly compensated for by a decreased HCO3 concentration. This resulted in only a slight respiratory alkalosis at extreme temperatures (+0.021 and +0.042 pH units at 42 and 45 degrees C, respectively). 4. Changes in Paco2 were negatively correlated with tidal volume: Paco2 (torr) = 33.10390 - 1.17493 VT(ml); r = -0.925, P much less than 0.001. 5. The present findings are consistent with an hypothesis that modulation of tidal volume during thermal panting might play a major role in acid-base regulation.