Energy (gross energy, GE) transfer based on chemical composition was s
tudied in 80 layer (White Leghorn, WL) eggs, in 80 broiler (New Hampsh
ire, NH) eggs between days 1 and 20 of incubation, and in 40 White Bei
jing duck eggs between days 1 and 25. Our data indicate that at the be
ginning of incubation, both NH and duck eggs contained substantially m
ore energy (450 +/- 18 kJ and 614 +/- 18 kJ, respectively) than WL egg
s (359 +/- 15 kJ). In the course of incubation, 30.8% of available ene
rgy was utilized by WL, 33.9% by NH, and 19.9% by Beijing ducks. Thus
the highest incubation efficiency was found in ducks. This is also ind
icated by their incubation power that reached only 45.5 mW. It was hig
her in WL and NH (63.9 and 88.3 mW, respectively). Similar results wer
e obtained when this power was calculated for the initial and metaboli
c egg mass. Also the formation and functioning of the new individual's
tissues (including the embryonic membranes and fluids) required the s
mallest GE amount in ducks (2.39 kJ.g(-1)), whereas in WL it increased
to 3.66 kJ.g(-1), and in NH to 4.12 kJ.g(-1). The transfer of one J o
f GE from the eggs into tissues of embryos (without membranes anf meco
nium) required 0.95 J in WL, 0.87 J in NH, and only 0.54 J in ducks. T
hese energy transfer processes did not become significant until the la
st 9 (in fowl) or 10 (in ducks) days of incubation. The almost exclusi
ve energy source during incubation were lipids. Protein energy amount
did not decrease significantly except for WL. These experimental data
confirm the older ones only in part. Some interspecies differences, or
iginating also from the fact that incubation of ducks lasts longer, ar
e smaller than intraspecies differences, those between layer and broil
er type of chicks. These facts show that the incubation energy transfe
r in avian species is not only variable but also adaptable.