Differential embryo development among Tibetan Chicken, DRW and Shouguang Chicken exposed to chronic hypoxia

Asian - Australasian Journal of Animal Sciences, March, 2009 by Mei Li, Chun-Jiang Zhao, Chang-Xin Wu

Embryo and various organ mass

At HH stage 39, 41, 43 and 45, the eggs were weighed, respectively. The survival individual was operated with surgical scissors to access to the internal organs of embryo. Brain, heart, liver, stomach, intestine and eyes were carefully isolated from the embryo. Then they were washed with 0.85% NaCl. The visible free liquid on the surface of the organ was removed. Furthermore, all the organs were weighed by electronic balance (Ohaus Corp. Pine Brook, NJ, USA). The scale is sensitive to 0.001 g. The number of the surviving individuals measured during the various portions of incubation was presented in Table 1.

Statistical analysis

Data were analyzed by least square analysis procedure of SAS (version 8.02, SAS Inst. InC., Cary, NC). The model was as follows: [Y.sub.ijk] = [micro] [A.sub.i] [B.sub.j] [C.sub.k] [A.sub.i]x[B.sub.j] [A.sub.i]x[C.sub.k] [B.sub.j]x[C.sub.k] [[epsilon].sub.ijk], in which the meanings of the items are as follows: [Y.sub.ijk], the embryo or organ mass; [micro], the overall mean; [A.sub.i], environment stress; [B.sub.j], breed difference; [C.sub.k], embryonic stage; [A.sub.i]x[B.sub.j], interaction effect of stress and breed. In analogy, [A.sub.i]x[C.sub.k] and [B.sub.j]x[C.sub.k] are interaction effect between two factors; [[epsilon].sub.ijk], the residual error. The egg mass at four different developmental stages was used as a covariate for embryo mass. The organ mass was normalized by body mass. All data are presented as means [ or -] SE. The significance levels were set at p<0.05 and p<0.01.

RESULTS

Hypoxic growth

Prior to incubation, fertilized eggs from T are much lighter than those from DRW and S (p<0.01) (Figure 1).

In hypoxia, in the three chicken breeds, there was significant difference in the embryo mass from stage 41 to 45 (p<0.01). For clarity of presentation, data for all the embryos and the key organs in all of the three chicken breeds incubated under hypoxic and normoxic conditions are presented in Table 1. It was obvious that T grew the fastest among all of the three chicken breeds at all studied embryonic stages in hypoxia. Interestingly, the embryo weight of DRW was similar to S at HH 39, and both of them were lower than T, though there was not significant difference in the embryo mass in all the three chicken breeds at HH 39. By HH 41, the embryo mass in T is much heavier than that in DRW (p<0.01) and S (p<0.05). However, there is no significant difference in the embryo mass of the two lowland chicken breeds (p>0.05). From HH 43 to 45, T gained more weight than DRW and S in hypoxia.

In hypoxia, significant effects of hypoxic exposure on brain mass of each species were showed at the four different developmental stages (p<0.01). However, the brain mass in all of the three chicken breeds at each developmental stage in hypoxic environment changed in a similar manner (p>0.05) (Figure 2). There are the same growth patterns for liver, stomach, intestine (data not shown) as well as eye (data not shown) in all of the three chicken breeds in hypoxia with the exception that T stomach mass was much lighter than those of DRW and S at HH 45 (p<0.05).

[FIGURE 1 OMITTED]

It was well known that the heart was the first organ to develop during chicken embryonic stages. Under hypoxic condition, heart mass altered significantly in the three chicken breeds (p<0.01). Obviously, the heart mass of DRW was much more than that of S and T at any developmental stage (Table 1).