Characteristics Of The Gas Exchange And Growth Of Tibetan Chicken Embryo Incubated At High Altitude

The metabolic and hatchability are impaired if chicken eggs laid at sea level are incubated at high altitude. The adverse effect of high altitude have been attributed to the change of gas exchange which is due mainly to the decrease of the atmospheric pressure with altitude and the decrease of the partial pressure of oxygen is the one of important factors. However, the eggs of Tibetan chicken can maintain higher hatchability when incubated at high altitude. So the present paper mainly analysis the reason of the higher hatchability of Tibetan chicken eggs incubated at high altitude by study the characteristics of gas exchange of Tibetan chicken embryos as well as the traits of eggs and development of embryos of Tibetan chicken. The results as followed:(1) To investigate the hatchability characteristics of Tibetan chicken at the high altitude, the eggs of Tibetan chicken and Dwarf chicken were incubated at Tibet (altitude: 2900m) and Beijing (altitude: 100m) respectively. The results showed that the hatchability of Tibetan chicken fed in Tibetan was 74.63%; however, when Dwarf chicken eggs was airlifted to Tibet from sea level, the hatchability of fertile eggs was decreased from 88.18% to 37.25%. It indicated that Tibetan chickens had the obvious adaptability to the high altitude. When the Tibetan chickens fed in Beijing were incubated at the high altitude, the hatchability (61.18%) was lower than that of Tibetan chicken fed in Tibet. The hatchability of Dwarf chicken fed in Tibet (51.09%) was higher than that of Dwarf chicken fed in Beijing at high altitude and the hatchability of the fertile eggs of the hybrid between Tibetan chicken fed at Tibet and Dwarf chicken fed at Tibet was 74.86%. It suggested that the incubated effect of Tibetan chicken eggs at the high altitude was possibly influenced by the raised environment of hens, but the more important factor was possible from inheritance.(2) By analyzing the physical characteristics of Tibetan chicken eggs, such as weight, shape index, the water content, eggshell thickness and so on, the findings showed that the egg weights of Tibetan chicken fed in Tibet (42.90g) were significantly smaller than that of Dwarf chicken fed in Beijing (60.95g) (P<0.05) and the egg shape index of Tibetan chicken fed in Tibet (1.382) were significantly lower than that of Dwarf chicken fed in Beijing (1.317) (P<0.05), but the water content, eggshell thickness and other characteristics were not different between two breeds. It indicated that the characteristics including egg weight, egg index and egg components might not be the main factors that affected the hatchability at high altitude.(3) Several relevant characteristics were determined including the conductance, thickness, surface area, density of pores in eggshells and the vascular density index (VDI) of the chorioallantoic (CAM) of Tibetan chicken and Dwarf chicken. The conductance of Tibetan chicken eggshell(0.14mg/d.mmHg.g) was significantly lower than the control (0.16 mg/d.mmHg.g, P<0.01), which was the result from the smaller functional pore areas of eggshells ( A_PZ / A_PD =0.584) . The VDI of the chorioallantoic (CAM) of Tibetan chicken embryos was lower than those of Dwarf chicken.(4)To study the oxygen carrying capacity of the blood of Tibetan chicken embryos incubated at high altitude, the blood gas, acid-base value and hematology were determined. The results showed the venous and arterialized partial pressure of O₂ of Tibetan chicken and Dwarf chicken embryos did not differ significantly on day 9¹2 (P>0.05) , but the Tibetan chicken embryos had a higher partial pressure of CO₂ than those of Dwarf chicken embryos (P<0.05) , which indicated that the Tibetan chicken embryos had higher metabolism than that of the Dwarf chicken embryos on the similar arterialized O₂ partial pressure. The results of Acid-base analysis showed that the Tibetan chicken embryos incubated at high altitude had the similar pH values with those incubated at sea level, which was a possibly beneficial effect on the regulated the o...