Water loss was determined during incubation in 80 eggs of the domestic
fowl, White Leghorn - LB and New Hampshire - NH (between the 1st and
20th day), and in 80 eggs of Beijing White ducks (between the 1st and
25th day). Our data have shown that, the lowest actual water content w
as found in NH eggs, the highest in the duck eggs. Water content decre
ased absolutely and relatively during incubation; 365 in LB, 500 in NH
and 312 mg/d in ducks. Water loss was higher in the first half of hat
ching. In the second half it was probably partly offset by water origi
nating from fats oxidized for energetic purposes; the offset made a th
ird in LB and NH, and still more in the ducks. Our results are somewha
t different from the literature data, the variability of which is cons
idered to be rather high in general. There were large shifts of water
among the egg components during incubation. Water totally disappeared
from the albumen, although it contained approximately three quarters o
f water was at the beginning of hatching. Already in the first half of
incubation, more than a third of water was transported to the embryo,
fetal membranes and fluids. In the subsequent ten days, water accumul
ation in the body of the developing and growing embryo was especially
rapid; the water amount increased eight times in the fowl, seven times
in the duck bodies.Water losses and its shifts show not only interspe
cific differences related to different lengths of incubation, but also
intraspecific ones, between BL and NH.