[Consequences of short term fluctuations of environmental temperatures in calves--Part 1: Immediate reactions of the respiratory system, the cardiovascular system, metabolism and thermal regulation].

Clinically healthy calves (aged 3-6 weeks) were exposed to defined ambient temperature for 4 hours (cold: 5 degrees C, 60% humidity, n = 12; warm: 35 degrees C, 60% humidity, n = 11). During the exposure of each animal in a climatic chamber, certain parameters of lung function, respiratory mechanics, blood gas analysis, circulation, metabolism and thermal regulation were registered simultaneously in order to study immediate physiological consequences of different environmental conditions. In comparison to control calves (18-20 degrees C, 60% humidity, n = 13) an insufficient adaptation of these young calves was noticed in both cold and warm conditions. At 5 degrees C, marked changes in lung function were observed, i.e. airway constriction, pulmonary hypertension, and ventilation-perfusion-mismatching leading to hypoxemia and hypercapnia. Due to compensation by the circulatory system, a sufficient O2-consumption of the organism as well as an unchanged body temperature were maintained. At 35 degrees C, the respiratory pattern changed to panting and a higher dead space ventilation. No changes were observed in pulmonary gas exchange and blood arterialisation. Due to hyperventilation, the partial pressure for CO2 decreased in blood. Since the body temperature increased continuously, thermal regulation was insufficient. This situation would have led to animals collapsing after a period of heat stress lasting longer than 4 hours. In conclusion, young calves up to the age of 6 weeks were not able to tolerate acute changes in ambient temperature. This was true for cold conditions (5 degrees C) as well as for hot conditions (35 degrees C). The results of this study should be taken into account in order to optimise transport and farming conditions.