This work was carried out in the Research Station for Animal Production (Faculty of Agriculture, Cairo University) to study the breed difference of native Rahmani and imported merino sheep in the structure of the respiratory system as related to heat tolerance. 12 animals from each breed were slaughtered to obtain the respiratory system for anatomical studies, 3 of each breed at 1, 4, 8 and 16 months of age. The main results were: The volume of the lung was larger in merino than in Rahmani (Egyptian native breed) sheep at all ages, nevertheless both breeds had an equal lung volume per 1 kg body weight at a given age. The native Rahmani breed has the privilege of larger dead space than the merino. The volume of the dead space was 125, 215, 291 and 386 cm3 in the Rahmani sheep and 76, 141, 195 and 251 cm3 in the merino at 1, 4, 8 and 16 months of age, respectively. The volume of respiratory space, on the other hand, was larger in the merino. It was 81, 182, 312 and 590 cm3 in the Rahmani and 90, 209 367 and 692 cm3 in the merino at the successive ages. The number of alveoli in the lung was greater in the merino than in the Rahmani. In both breeds, the number of alveoli in the lung increased with age up to 8 months. There was a high negative correlation between density and size of alveoli in both breeds. The merino had a vast surface of alveoli. The respiratory surface of the alveoli in the lung was around 11, 19, 30 and 43 m2 in the Rahmani, 13, 23, 37 and 55 m2 in the merino at 1, 4, 8 and 16 months of age. The native Egyptian sheep possessed a greater ratio deadspace/respiratory space than the merino. This is an anatomical adaptation of the Egyptian (subtropical) breed for efficient heat dissipation via the respiratory system without interference with the C02 and alkali reserve in the body.

Keywords:
Sheep, Respiration, Heat tolerance
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© 1978 S. Karger AG, Basel
1978
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