Blood gas, hemoglobin, and growth of Tibetan chicken embryos incubated at high altitude.

Metabolism and hatchability are impaired when chicken eggs laid at sea level are incubated at high altitude. The Tibetan chicken is an excellent local poultry breed that inhabits altitudes of 2,900 m and has a hatchability of approximately 75% at that altitude. To understand how Tibetan chicken embryos develop successfully at high altitude, we compared blood gas, pH, hemoglobin concentrations and embryo mass for Tibetan chicken embryos (T) and for embryos from a dwarf breed (D) that normally is reared at sea level. The 2 breeds (T and D) and 2 incubation altitudes (2,900 m = high, H; and 100 m = low, L) were compared at 9, 12, 15, and 18 d of incubation. Embryo weights were lower for the high altitude groups (TH, DH) than for the low altitude groups at all stages of incubation. The embryo mass of TH appeared to increase more quickly than that of DH. Compared with DH, TH embryos had lower arterialized oxygen partial pressure on d 18, higher venous carbon dioxide partial pressure from d 12 to 18, and higher hemoglobin concentration and lower venous blood pH values on d 12 and 15. These findings indicate that the ability of the Tibetan chicken embryos to adapt to the high altitude may be due to the increase in hemoglobin concentration, which augments the blood oxygen-carrying capacity. In addition, the higher venous carbon dioxide partial pressure and lower venous blood pH promote unloading of oxygen from hemoglobin.