FUNCTIONAL AND METABOLIC CHANGES IN RABBITS UNDERGOING CONTINUOUS HEAT-STRESS FOR 24 DAYS

Intensively reared rabbits are particularly sensitive to heat stress. For this reason if is useful to identify reliable stress indicators to evaluate peculiar stress conditions of the breeding environment. In order to recognize which changes in biochemical and functional measurements can be utilized as stress indicators, three groups of eight New Zealand White rabbits, of 2.8 kg body weight and 11 weeks of age, were kept in individual cages and submitted to different environmental conditions. Group 1 was located in a climatic chamber at 33.5 (s.e. 0.5)degrees C and relative humidity 0.62 (s.d. 0.05) and groups 2 and 3 (control) at 18.0 (s.d. 0.5)degrees C. Group 1 was given ad libitum a commercially pelleted diet, group 2 was pair-fed with group 1, and group 3 was given food ad libitum. For all the groups, at days 0, 1, 6, 12 and 24, the following measurements were made: body weight, rectal temperature, food consumption and plasma glucose, cholesterol, urea, triglycerides, uric acid, and glutamate oxalacetate transaminase, glutamate pyruvate transaminase, thiobarbituric acid-reactive substances, vitamin A and vitamin E, SH-groups and total (peroxil) radical-frapping antioxidant parameter (TRAP). Food consumption of animals exposed to 33.5 degrees C was strongly reduced in the 1st day (13.6 v. 161.6 g/day); a gradual increase until the end of the trial was then observed (98.8 v. 177.3 g/day). Rectal temperature rapidly increased and remained stable and higher than in the control groups all through the trial (P < 0.01). The major changes in the measurements of the heat stressed animals were a significant increase of the plasma level of vitamin E at days 6, 12, 24 (P < 0.05), and a significant reduction of the plasma concentration of SH-groups and TRAP (P < 0.05). The results suggest all impairment or overload of antioxidant systems after thermal stress, indicating a reduced resistance to biological and environmental stress factors. The results also indicate that some parameters of antioxidant systems can be used to select a significant stress indicator.