Adaptation of homeostatic thermoregulation: comparison of incubating and non-incubating Bantam hens

Summary Incubating and non-incubating Bantam hens were exposed to identical thoracic skin cooling to study the difference between their physiological responses with regard to thermoregulatory adaptation to incubation. Under resting conditions thoracic skin temperature (T _ths) and metabolic heat production (M) were significantly higher in broody than in non-broody hens, indicating a permanently increased conductance of the brood patch. Thoracic skin cooling from 35 to 25 °C decreased T _ths less in broody than in non-broody hens. In broody hens, these coolings induced a large, immediate increase in M, no constriction of brood patch vasculature, and a decrease in colonic temperature (T _c). This decrease in T _c triggered no further increase in M, but induced vasoconstriction in the feet. The coolings induced a smaller increase in M in the non-broody hens, accompanied by pronounced vasoconstriction, and did not affect T _c and foot temperature, T _f. The effects of more severe thoracic skin cooling (between 25 and 15°C) differed much less between non-broody and broody hens. Vasoconstriction of the brood patch also occurred in the latter. It is concluded that in adaptation to incubation the thoracic skin becomes more sensitive, and its input signal becomes stronger for the control of certain effector systems of thermoregulation, allowing a controlled heat transfer to the eggs.Abbreviations BM body mass - M metabolic heat production - T _c colon temperature - T _ths thoracic skin temperature - T _f foot temperature - T _bs back skin temperature - T _stim stimulation temperature - VO₂ oxygen consumption     

Arterial hypotension in ducks adapted to high salt intake

Summary A homogeneous group of 8-week-old Pekin ducks was divided into two groups: saltwater (SW) ducks received salt water of gradually increasing salinity (200–600 mOsm·kg^-1) from the 8th to 20th week of age; freshwater (FW) ducks were maintained on fresh water but otherwise treated identically. During the course of salt-adaptation SW ducks increased plasma osmolality, Na⁺ and Cl^- levels, and concentrations of the osmoregulatory peptide hormones arginine vasotocin and angiotensin II. The apparent volume of inulin distribution decreased in SW ducks, but blood volume was not reduced. SW ducks also developed arterial hypotension, bradycardia, and reduced cardiac output in the course of salt adaptation. This depressed cardiovascular performance was associated with enhanced vagal restraint of cardiac function and reduced plasma concentrations of norepinephrine. Salt water adaptation did not alter the degrees to which mean arterial pressure and heart rate changed in response to intravenous bolus injections of catecholamines. The same applied to the osmoregulatory peptides which were, however, effective only at supraphysiological concentrations. The Pekin duck, as a bird predisposed for adaptation to high salt loads, presumably adapts to chronic hypertonic saline intake by resetting the central autonomic control of blood pressure to a lower level.Abbreviations FW ducks fresh water ducks - SW ducks salt water ducks - ANGI angiotensin II - AVT arginine vasotocin - MAP mean arterial pressure - HR heart rate - IV intravenous - CO cardiac output - SV stroke volume - TPR total peripheral resistance - ISp virtual inulin space - ECFV extracellular fluid volume     

Cardiovascular responses to thoracic skin cooling: comparison of incubating and non-incubating Bantam hens

Summary Body temperatures, metabolic rate, haemostatic parameters, and cardiovascular reactions to thoracic skin cooling were compared between incubating (broody) and non-broody Bantam hens. Under resting conditions, without thoracic skin cooling, cardiac output of broody hens was twice that of non-broody hens. However, their metabolic rate was increased by only one-third over that of non-broody hens, and the arteriovenous difference in oxygen concentration was smaller for broody birds. This indicates a higher rate of non-nutrient blood flow during incubation. A higher thoracic skin temperature (T _ths) for broody hens compared to non-broody hens suggests that brood patches are the probable site of this increased flow through arteriovenous anastomoses (AVAs). Thoracic skin cooling increased metabolic rate and significantly more in broody hens, but did not increase AVA blood flow. The relation between metabolic rate and total peripheral resistance indicated more intense vasodilation for broody hens at the relatively low metabolic rates during moderate cooling, and more intense vasoconstriction for the broody hens at the high metabolic rates during stronger cooling. This corresponds to T _ths measurements indicating dilation of brood patch AVAs with moderate cooling and AVA constriction with severe cooling. During moderate cooling, vasoconstriction in the feet and wattles of broody hens (but not of non-broody hens) freen non-nutrient blood flow for redistribution to the brood patches. Thus, the cardiovascular system of the hen seems to adjust to the special demands of incubation by a permanent increase of AVA flow in the brood patch, and by an additional capacity for brood patch vasodilation induced by cold stimuli in the range from 35 to 25°C. This corresponds well to the temperature range for development of galliform embryos.Abbreviations AVAs arteriovenous anastomoses - BP arterial blood pressure - CaO₂ and CvO₂ arterial and venous oxygen concentrations, respectively - HR heart rate - MAP mean arterial blood pressure - cardiac output - SV stroke volume - T _bs back skin temperature - T _c cofon temperature - T _f foot temperature - T _ths thoracic skin temperature - TPR total peripheral resistance - T _w wattle temperature - oxygen consumption