Oct. is, 1924 Postnatal Growth of the Single-Comb White Leghorn 367 
GROWTH OF THE BODY AND PARTS 
GROWTH IN BODY WEIGHT 
Growth in body weight is but an 
incidental and subordinate part of the 
problem. The increase in the gross 
body weight of the White Leghorn 
chick has been worked out thoroughly 
and for a large number of chicks by 
Philips (20 ), Card and Kirkpatrick 
(2), Buckner (1), and others. The 
weighing of the chicks for the present 
experiment was undertaken chiefly to 
serve as a check upon the individuals 
selected for the autopsies. It will be 
shown, however, that the various 
groups in the present experiment give 
some information on the relative effects 
of certain kinds of food and care upon 
growth of the chickens. A reduction 
of 23 days in the period between 
hatching and egg production (as in 
Group 3 compared with Group 1), is a 
matter of practical interest. The im¬ 
portance of the time of hatching is 
also indicated by the slow growth of 
Group 4, a late-hatched group. 
Figure 1 4 shows the three phases 
of the postnatal growth of the entire 
chicken, which are as follows: A period 
of relatively slow increase in weight; 
a period of rapid growth; a decrease 
after the time of sexual maturity is 
reached, with the resulting flattening 
(horizontal tendency) of the curve. 
The irregularities in the terminal por¬ 
tion of the curve (especially notice¬ 
able in Figure 1) are due in part to 
the much smaller number of specimens 
weighed in the later periods. Any 
individual fluctuation consequently 
would modify the curve to a much 
greater degree. 
The growth curves of the individual 
groups were plotted but not shown with 
the accompanying charts. The slow 
growth of Group 4 was very noticeable. 
In Groups 1 and 3 there is a slight flat¬ 
tening of the curve for the females at 
about 150 days for Group 1, and 130 
days for Group 3, or about 40 days be¬ 
fore egg-laying began. This would sug¬ 
gest a prepuberal pause in growth, 
which does not occur in other domestic 
animals. The significance of this pause 
is questionable. 
The growth data as given by the pre¬ 
vious investigators, when plotted on 
the same scale as the present figures, 
are of interest for comparison. The 
data of Philips (20) and Card and Kirk¬ 
patrick (2) include only the weights of 
the females after it is possible to sepa¬ 
rate the males. Buckner and others 
(. 1 ) give the data for males and females 
separately. For comparison, the data 
for the two sexes are here grouped to¬ 
gether up to the ninth week. When 
the growth curves are compared it is 
seen that the average weight of the 
chickens used in the present work falls 
below the other three at first. It 
never runs so high as the curve con¬ 
structed from the data of Card and 
Kirkpatrick. They carried their weigh¬ 
ings only through the twenty-fourth 
week, but at this time the chickens (fe¬ 
males only) averaged 1,489.12 gm. 
while the Minnesota chickens averaged 
1,298.44 gm. The chickens reported 
by Philips (20) from the Indiana Ex¬ 
periment Station were heavier than 
those discussed in the present paper* 
up to the thirteenth week, when both 
groups averaged about 650 gm., but 
from this time on they were a very 
little lighter. The Indiana experiment 
was continued for only 24 weeks, at 
which time the chickens averaged 
1,248.50 gm., while the writer’s aver¬ 
aged 1,298.44 gm. 
The curve constructed from the 
data on the growth of the chickens re¬ 
ported by Buckner and others (1) from 
the Kentucky Experiment Station is 
more irregular than any of the others. 
It also runs higher than the present 
series up to between the thirteenth and 
fourteenth weeks, then it falls below. 
At the end of the 28 weeks the pullets 
from the Kentucky station averaged 
1,447.5 gm. for the hen hatched and 
reared, and 1,120.4 gm. for the artifi¬ 
cially hatched and reared pullets, as 
compared with 1,539.0.6 gm. for the 
artificially raised Minnesota pullets. 
The Minnesota cockerels likewise aver¬ 
age lighter than both the artificially 
and the hen-raised Kentucky cockerels 
up to the nineteenth and twentieth 
weeks. After this time the cockerels 
of the present investigation were heav¬ 
ier than the Kentucky artificially 
4 KEY TO FIGURES 
Solid dot. —Weight or measurement of the males (except in figure 27). 
Circle.—W eight or measurement of the females (except in figure 27). 
Adult. —Adult chickens (the three older cockerels and the three two-year-old hens). 
Heavier lines— Curves of growth of absolute weight (measured in grams) or measurements (in 
centimeters), all drawn according to formula, except Figure 1. 
Lighter lines. —Curves of relative weight or percentage of the net body weight. Individual cases not 
shown. 
Y (ordinates).— (On left margin) weight of the part in grams or length in centimeters; (on the right 
margin) percentage of the net body weight. 
X. (abscissae).— Gross body weight in grams, or age in days. 
