PLASMA-VOLUME CONSERVATION IN PIGEONS - EFFECTS OF AIR-TEMPERATURE DURING DEHYDRATION

We assessed the effects of the ambient air temperature prevailing duri ng dehydration, which included complete water and food deprivation, on plasma volume (PV) conservation in pigeons (Columba livia) exposed to air temperatures of 25 degrees C (n = 7), 36 degrees C (n = 12), and 40 degrees C (n = 24). The pigeons were dehydrated for 65.4, 32.3, and 27.7 h, on average, at 25, 36, and 40 degrees C, respectively. Dehydr ation rates averaged 5, 10, and 15.2% of initial total body water (TBW ) per day at the three air temperatures, in ascending order. Birds exp osed to 25 and 36 degrees C maintained PV despite the fact that they l ost, on average, 14 and 17.3% of their TBW, respectively. In contrast, PV in pigeons exposed to 40 degrees C decreased by 8.9%, even though the reduction in TBW (17.7%) was similar to that incurred at 36 degree s C. Mean plasma osmolalities reached 347.7, 345.6, and 374.8 mosmol/k gH(2)O at 25, 36, and 40 degrees C, respectively. No significant chang es occurred in hematocrit (Hct) and hemoglobin concentrations (Hb) dur ing dehydration at 25 and 36 degrees C. However, at 40 degrees C Hb in creased by 8.2% with no change in Hct, indicating a decrease in red bl ood cell volume (RBCV). The results of this study suggest that mainten ance of PV and RBCV is affected not only by the dehydration level atta ined but also by the ambient conditions under which dehydration is ind uced and the rate at which dehydration takes place.