BREED AFFECTS THERMOREGULATION AND EPITHELIAL MORPHOLOGY IN IMPORTED AND NATIVE CATTLE SUBJECTED TO HEAT-STRESS

The objective of this study conducted in tropical Brazil was to charac terize some physiological and histological responses to heat stress in imported Bos taurus, native Bos taurus, and native Bos indicus cattle . Imported Simmental (n = 107), native Simmental (n = 99), and native Bos indicus cattle (n = 121) (42 to 80 mo of age) were evaluated. Anim als were walked 7 km at 37 degrees C and 60 to 65% relative humidity d uring midday. Rectal temperatures and respiration rates were taken bef ore and after the walk. A .01-cm(2) sample of cutaneous tissue from th e lateral cervical region was obtained from each animal. Slices were s tained with hematoxylin-eosin solution, and the epithelial strata were counted. Perimeter of the sweat glands was also calculated. Rectal te mperatures before the walk were greater (P <.001) in imported Simmenta l (40.52 +/- .04 degrees C) than in native Simmental (38.92 +/- .04 de grees C) or Bos indicus (38.90 +/- .04 degrees C). Rectal temperatures after the walk were greater (P < .001) in native Simmental (39.87 +/- .05 degrees C) than in Bos indicus (39.46 +/- .05 degrees C). Because of the heat, imported Simmental were not capable of finishing the dri ve, and rectal temperatures could not be taken. Respiration rates befo re and after the walk were greater (P < .001) in imported Simmental (6 4.3 +/- .6; 95.8 +/- .8) than in native Simmental (35.0 +/- .6; 56.8 /- .8) or Bos indicus (15.0 +/- .2; 33.2 +/- .8). Sweat gland perimete r was greater (P < .001) in Bos indicus (540.5 +/- 19.1 mm) than in na tive Simmental (382.0 +/- 27.6 mu m) or imported Simmental (497.2 +/- 17.4 mu m) Native Bos indicus were environmentally adapted, native Sim mental had elevated body temperatures and respiration rates, and impor ted Simmental had dramatically increased body temperatures and respira tion rates. Native Bos indicus cattle were environmentally adapted and differed in skin histology, sweat gland histometry, and number of epi thelial strata.