Effects of Immobilization, Heat Stress and Antioxidant Supplementation on Thermoregulation and Haematological Responses in Male Rabbits (Oryctolagus cuniculus)

Background and Objectives: Immobilization stress may induce negative effects on physical and physiological activities of humans and animals. Heat stress also influences the health and survival of mammalian species, particularly under tropical conditions. The objective of the study was evaluation of the responses to immobilization (IMO) and acute heat stress (HS) in a rabbit model. The potential protective effects of administration of antioxidants on IMO and acute heat stress (HS) were also assessed.

Materials and Methods: Sixty six male rabbits (mean body weight , BW: 1582±28 g) were used in three trials to investigate the effects of HS , IMO+HS and administration of vitamin C (IMO+HS +Vit C) or vitamin E-selenium (IMO+HS+VitaminE-Se). Immobilization was performed by fixing the animals in a specially designed box; HS was induced by exposing rabbits to direct solar radiation (370 W/m2) for 1 hour (trial 1) and 2 hours (trials 2 and 3). The body weight (BW), rectal temperature (Tr) and heart rate (HR) were monitored and venous blood samples were collected before the beginning of the trial and then at 2, 24 and 48 hours after the end of the trial. The packed cell volume (PCV), total leukocytes count (TLC) and differential leukocytes count (DLC) were determined.

Results: In trial- I, 18 rabbits were randomly assigned to 3 groups of 6 each (control, HS and IMO+HS). HS rabbits showed higher values of HR (P<0.01) compared to IMO+HS rabbits. In trial -II, 24 rabbits were assigned to 4 groups comprising control, HS, IMO+HS (received 2 doses of normal saline) and IMO+HS +Vit. C (received 2 doses of 300 mg/kg/BW each Vit. C subcutaneously). IMO+HS animals had higher responses compared to HS, as evidenced by significantly (P<0.01) higher values of Tr and HR. Administration of Vit. C decreased Tr, and maintained HR and haematological parameters relatively constant. In trial 3, 24 rabbits were assigned to 4 groups comprising control (received 2 doses of normal saline s/c), HS, IMO+HS and IMO+HS +Vit. E-Se (received 2 doses 100 mg/kg/BW each Vit E-Se s/c). The responses of animals to IMO+HS were greater compared to HS alone. IMO+HS significantly (P<0.001) increased Tr and HR. Furthermore, IMO+HS rabbits showed significant (P<0.001) decreases in PCV and TLC after 48hrs and 24 hours, repectively, compared to the values of control rabbits. Administration of Vit.E-Se decreased Tr, HR and maintained haematological parameters relatively constant.

Conclusion: Immobilization aggravated the negative effects of heat stress, while Vit. C was more effective than Vit.E-Se in alleviation of hyperthermia and maintaining normal haematological parameters in rabbits.