Skin biopsies of different cattle breeds were histologically exa mined in an attempt to correlate between skin morphology and heat tolerance:
The thickness of the straturn cornium, epidermis, and thermos tate layer, and the depth of the sweat glands, sebaceous glands, and hiar bulbs were determined.
Morphological types of the sweat glands were described and illustrated by photomicrograpl.s. The bag-shaped sweat glands predominate in the skin of Native cattle (Baladi) and hajf cross breds, while the tubular and intermediate types predominate in Friesian, and 3/, cross-breds of both Friesian and Hereford. Den sity and dimensions of the sweat glands and their sweating surface per single gland and per square cm. were measured and calculated. Breed differences in skin structure were characterised.
The relationship between heat tolerance, evaporation rate and sweat gland density, and their secretory surface was discussed.
It was concluded that, the sweat gland type as well as its depth and sweating surface, are the most skin parameters correlated to heat tolerance.
These factors may be considered as indices for selection of Euro pean breeds introduced to subtropical countries.