Differences in skin characteristics in European (Large White) and Caribbean (Creole) growing pigs with reference to thermoregulation

The effects of breed and season on histological skin characteristics were studied at the experimental facilities of INRA in Guadeloupe (16 degrees Lat. N., 61 degrees Long. W.) in two replicates using a total of 20 Creole (CR) and 20 Large White (LW) pigs. The first replicate was carried out during the warm season (i.e., between February and April) and the second during the hot season (i.e., between August and October). In the warm season, ambient temperature and relative humidity averaged 25.3 degrees C and 86.0%, respectively. The corresponding values for the hot season were 27.9 degrees C and 83.6%. At 90 kg BW, all pigs were slaughtered and a 2 to 4 cm(2) sample of cutaneous tissue from the back region (i.e., at the last dorsal rib level) was taken from each animal before scalding and dehairing. Slices were stained with trichrome blue staining and the thickness of the epidermis and dermis were determined. The density and surface of the sweat glands (SG) were also determined. The mast cell density was measured using slices stained with Giemsa. Epidermis thickness was not affected by breed or season and averaged 55 mu m. However, dermis thickness was significantly higher in CR than in LW pigs (3.60 vs. 3.13 mm; P < 0.01) but it was not influenced by season (3.36 mm on average; P = 0.17). The density of SG was significantly higher in CR than in LW pigs (32.0 vs. 25.4 SG per mm(2); P < 0.01) but their surface area was lower in CR than in LW pigs (106 vs. 263 x 10(-3) mu m(2) per mm(2); P < 0.01). The SG density tended to be higher in the hot than in the warm season (30.4 vs. 26.9 SG per mm(2); P = 0.0971). Mast cell density in the dermis was found to be higher in CR than in LW pigs (2.52 vs. 1.38 mast cells per mm(2); P < 0.01). Irrespective of the breed, mast cell density was higher during the hot than the warm season (2.22 vs. 1.68 mast cells per mm(2); P < 0.01). In conclusion, our study suggests that the differences in skin histology and/or sweat gland histometry could partly explain the better heat tolerance in CR pigs.