EFFECTS OF DEHYDRATION ON THE HEAT TOLERANCE OF MALE AND FEMALE NEW-ZEALAND WHITE-RABBITS

Male and female New Zealand White rabbits were exposed for 3 h to 34-degrees-C and 36-degrees-C (both at 40% r.h.) when hydrated and dehydrated. Females had lower rectal and skin temperatures and respiratory rates than males (P < 0.001). Differences between the sexes in rectal temperature were greater at 36-degrees-C than at 34-degrees-C. Withholding water for 24 h significantly increased the responses in rectal temperature; the differentials between hydrated and dehydrated males and females being 0.3-degrees-C and 0.2-degrees-C, respectively. In contrast, respiratory rates were lower in dehydrated than in hydrated rabbits, suggesting that the former were attempting water homeostatis at the expense of thermoregulation. The results suggest that the performance of rabbits in the tropics is likely to be maximized when drinking water is available at all times, and that of males, particularly breeding bucks, might be improved simply by housing them in the coolest available location. Significant individual differences in observed responses point to the need for genetic studies of heat tolerance and the possibility of developing better adapted genotypes.