Growth and development of giant panda (Ailuropoda melanoleuca) cubs at Beijing Zoo

Abstract

We studied the postnatal body weight gain and development of 11 male and nine female giant panda Ailuropoda melanoleuca cubs born at Beijing Zoo from 1985 to 1998. Growth rates of the cubs appeared to be sexually dimorphic from the fourth month after birth; the male grew slightly faster than the female cubs. Growth rates between artificially fed and naturally fed cubs were significantly different from the fourth month after birth. The growth rate of the artificially fed cubs was slightly higher than that of the cubs fed by their mothers, indicating that the substitute milk satisfied the nutrient needs of the cubs. The body length of the cubs increased rapidly after birth; 8-month-old cubs were three times longer than newborn cubs. Chest circumferences of 8-month-old cubs also increased to twice that of newborn cubs. Tail length relative to body length was reduced from 14.9% at birth to about 8.6% in 8-month-old cubs. Cubs started to grow teeth when they were 3 months old. By the age of 1 year, the cubs had fully grown deciduous teeth. The teeth formula of one 1-year-old cub was 2·1·3·0/2·1·3·0=24. We recorded the changes in fur colour, development of the sense organs and limbs of the giant panda cubs. Finally, we compared the body weight and life-history parameters of giant pandas with those of bears and raccoons and discussed the management regime for the care of captive-born giant panda cubs.

Full text

Growth and development of giant panda (Ailuropoda
melanoleuca) cubs at Beijing Zoo
Jianjun Peng
1
, Zhigang Jiang
1
*, Weixing Liu
2
, Shiqiang Huang
2
, Jingguo Zhang
2
and Wanming Wang
2
1
Institute of Zoology, Chinese Academy of Sciences, Beijing, 100080, China
2
Beijing Zoo, Beijing, 100080, China
(Accepted 28 July 2000)
Abstract
We studied the postnatal body weight gain and development of 11 male and nine female giant panda
Ailuropoda melanoleuca cubs born at Beijing Zoo from 1985 to 1998. Growth rates of the cubs appeared to
be sexually dimorphic from the fourth month after birth; the male grew slightly faster than the female cubs.
Growth rates between arti®cially fed and naturally fed cubs were signi®cantly different from the fourth
month after birth. The growth rate of the arti®cially fed cubs was slightly higher than that of the cubs fed
by their mothers, indicating that the substitute milk satis®ed the nutrient needs of the cubs. The body
length of the cubs increased rapidly after birth; 8-month-old cubs were three times longer than newborn
cubs. Chest circumferences of 8-month-old cubs also increased to twice that of newborn cubs. Tail length
relative to body length was reduced from 14.9% at birth to about 8.6% in 8-month-old cubs. Cubs started
to grow teeth when they were 3 months old. By the age of 1 year, the cubs had fully grown deciduous teeth.
The teeth formula of one 1-year-old cub was 2130/2130 = 24. We recorded the changes in fur colour,
development of the sense organs and limbs of the giant panda cubs. Finally, we compared the body weight
and life-history parameters of giant pandas with those of bears and raccoons and discussed the manage-
ment regime for the care of captive-born giant panda cubs.
Key words: giant panda, Ailuropoda melanoleuca, growth, development, bear, lactation
INTRODUCTION
Neonatal and early periods are known to be the times of
high risk of mortality in captive-born wild animals.
Knowledge of growth and development of these animals
in relation to the management regime is vital for
attempts to improve the survival of young born in
captivity (Kirkwood & Mace, 1996). The giant panda
Ailuropoda melanoleuca is a species that is endangered as
a result of its fragmented habitats and low fecundity in
the wild. It is also dif®cult to breed the giant panda in
captivity because of the low fecundity rate and high cub
mortality. Sexual maturity of the female giant panda
ranges between 5.5 and 6.5 years old, and for males is
c. 6.5±7.5 years old (Hu, 1988). Forty-three zoos and
nature reserves world-wide kept more than 240 giant
pandas from 1936 to 1989 (Hu, 1988; Wang, 1990). But
only about 30 females and no more than 20 males,
which were c. 20% of the adult giant panda population
in captivity, had a natural ability to mate. Two hundred
and twenty three cubs were born in zoos and conserva-
tion breeding centres world-wide during 1963±99, but
109 of the cubs died within 30 days after birth; mortality
was as high as 48% (Xie & Gipps, 1999). Furthermore,
not > 30% of the captive born cubs survived for > 3
years (Huang, 1994; Feng, Huang et al., 1997; Li et al.,
1999; Xie & Gipps, 1999).
There may be many reasons for the low reproductive
success in the giant panda. One factor may be the low
birth weight of cubs and their underdeveloped organs at
birth. Body weights of adult giant pandas generally
range between 80 and 125 kg, and some may reach
182 kg. But compared with adult giant pandas,
newborn cubs are very small, and weighed mostly
90±131 g (average 104.2 g), only c. 0.08±0.13% of the
body weight of their mothers (Hu et al., 1985; Liu, Xie
et al., 1994; Ma, Hu & Zhai, 1994). How to care for
captive-born cubs to achieve optimum growth and how
to reduce the risk of death in cubs has become central to
the conservation of the giant panda. Thus, it is essential
to understand the growth and development patterns of
giant panda cubs, about which there is little information
in the scienti®c literature. We studied the postnatal
body weight gain and development of giant panda cubs
born at Beijing Zoo.
*All correspondence to: Z. Jiang, Institute of Zoology, Chinese
Academy of Sciences, Beijing, 100080, China
J. Zool., Lond. (2001) 254, 261±266 #2001 The Zoological Society of London Printed in the United Kingdom

MATERIALS AND METHODS
The postnatal body weight gain and development data
on 11 male and 9 female giant panda cubs born in
Beijing Zoo from 1985 to 1998 were recorded.
In Beijing Zoo, the temperature of the delivery rooms
for giant pandas was maintained between 18 and 22 8C
and relative humidity was maintained between 65% and
80%, while the temperature in the incubators for giant
panda cubs was maintained between 33 and 35 8C and
relative humidity between 65% and 70%.
All the cubs were closely observed for 1 year after
birth. Generally, most of the mothers who gave birth to
a single cub breast-fed their cubs. However, mothers
who gave birth to twins usually only fed 1 cub and
abandoned the other. The abandoned cubs were then
immediately taken out, weighed, measured and fed with
substitute milk formulated on cow's milk. Additionally,
some of the mothers could not feed their cubs well
because of lack of breast milk, and these were hand fed.
In Beijing Zoo, 5 cubs were abandoned by their mothers
and arti®cially fed after birth, while the other 15 cubs
born during 1985±98 were fed by their mothers. The
abandoned cubs were fed 3 times daily at 9:00±11:00,
16:00±18:00 and 22:00±24:00. We gradually increased
the quantity of milk fed to the cubs according to their
body weight and age while we reduced the feeding
frequency (1±2 times/day) as the cubs grew. We supple-
mented 50±100 g porridge to the milk per day and
gradually increased the amount of supplement porridge
to 100±200 g/day. Everyday, we also supplemented
50±100 g sugar, 3±6 g salt, 4±7 g calcium, 418 IU VitA,
61 IU VitD, 6.8 mg VitC, 85 mg VitK, 0.73 mg VitB
1
,
0.17 mg VitB
2
, 0.14 mg VitB
6
, 2.2 mg VitB
12
to the cow's
milk. When the teeth were growing, we supplemented
calcium (180±210 mg/kg body weight/day) to the cubs.
The cubs were weighed with an electronic scale to
the nearest g every 30 days when the cub was 1 to 12
months old. During this period, their body lengths
(from nasal tip to the end of tail) and chest circum-
ferences were measured and recorded with a tape and
the tail length with v. c. callipers to the nearest mm.
The change of fur colour, the eruption and growth of
teeth, the development of the limbs and the olfactory,
visual, auditory and gustatory sense organs were re-
corded. An alcohol tampon was used near the nares of
1 male cub, Yongliang, which was born on 14 Sept-
ember 1992, to test his olfactory sense every morning.
The cub's eye-opening time and its reaction to lights
were observed. Hearing was checked by gently clapping
our hands near the newborn cubs to see if they reacted
to sound. The suckling rates and food consumption of
the cubs were measured, and the relation between the
panda mothers and their cubs was observed. We ®tted
the growth data of the male and female cubs with
regression curves, and compared the difference between
the growth rates of males and females (1-way
ANOVA). The growth data of male cubs were ®tted
with the equation: BW(g) = 1396.8age(month)
1.3406
, and
for the female cubs: BW(g) = 1187.8age(month)
1.3622
.
Furthermore, the growth rates of the arti®cially fed
cubs were compared with those of the naturally fed
cubs (1-way ANOVA). All giant pandas in this study
were cared for in accordance with the principles and
guidelines of the Chinese wildlife management
authority.
RESULTS
Body weight gain
ANOVA indicated that the growth rates of male and
female cubs were not signi®cantly different during the
®rst 3 months after birth (P> 0.05, Table 1, Fig. 1), but
the growth rates for male and female cubs were signi®-
cantly different from the fourth month after birth
(P< 0.05, Fig. 1). ANOVA also indicated that the growth
rates between arti®cially fed and naturally fed cubs were
not signi®cantly different during the ®rst 3 months after
birth (P> 0.05), but were signi®cantly different from the
fourth month after birth (P< 0.05; Fig. 2).
Body development
The limbs of newborn cubs are weak; the cubs cannot
stand up. Two-month-old cubs can move around,
although this ability differed considerably among
J. Peng ET AL.262
y
= 1396.8
x
1.3406
r
2 = 0.999
Male
Female
y
= 1187
x
1.3622
r
2 = 0.9984
45000
40000
35000
30000
25000
20000
15000
10000
5000
123456789101112
0
Age (months)
Body weight (g)
Fig. 1. Growth curves of male and female giant panda
Ailuropoda melanoleuca cubs in Beijing Zoo.
Maternally fed
Artificially fed
45000
40000
35000
30000
25000
20000
15000
10000
5000
123456789101112
0
Age (months)
Body weight (g)
50000
Fig. 2. Growth curves of the arti®cially fed and breast fed
giant panda Ailuropoda melanoleuca cubs in Beijing Zoo.

individual cubs. Two and half months after birth, the
cubs can walk several steps. Four-month-old cubs can
run several steps. The cubs often climbed up their
mother's back to play, and when they slipped off, they
would climb up their mother's back again. Another half
month later, the cubs walked more often, sometimes
they even ran, though the support ability of their limbs
was still not strong. During this period, cubs followed
their mothers to the outdoor activity ground. While the
mother was eating bamboo, the cubs ®ddled with the
bamboo leaves, though they were unable to eat the
leaves. Five and half months after birth, some cubs
started to climb trees.
The body length of the cubs increased rapidly after
birth (Table 2). When they were 8 months old, their
body length tripled (Fig. 3). Chest circumference of
8-month-old cubs also increased to twice that of
newborn cubs. The tail length of newborn cubs was
about one-third of the body length. By 45 days old, the
tail length was only about one-quarter of their body
length. As the cubs grew, the relative tail length was
further reduced, until it was only about 8.6% of body
length in 8-month-old cubs.
The heads of the cubs were ¯atter than those of
adults. As the cubs grew, their heads became rounder,
their facial parts became shorter, and their skulls and
foreheads became higher than those of the newborn
cubs. The obliquity from the skull vertex to nasal tip
was about 65±708in cubs of 6±12 months old.
The cubs sometimes cried `En-en-en' or `Ya-ya-ya',
like a newborn human baby, and sometimes the cubs
cried `Gu-gu-gu', like the yip of newborn dogs. Fre-
quency of cry in cubs gradually decreased as their age
increased. The cubs also cried `Ji-a' during the early
4 days after birth, the cry frequency was 9±14 times/h,
then decreased to 4±6 times/h 5±20 days after birth.
Human baby-like cries and dog-like yips disappeared
when the cubs reached 2 months old. Cubs older than
2 months only hummed occasionally.
The eyes of newborn cubs are tightly closed. Their pink
bodies were covered with sparse white hairs 0.5 cm long,
but their head, limb and tail hairs were only c. 0.2 cm
long. Fur colour of the cubs changed as the cubs grew
up (Table 3).
Growth and development of teeth
Teeth formula was 2130/2130 = 24 in 1-year-old
cubs. Cubs started to grow teeth at 3 months old
(Table 4). By the age of 1 year, cubs had fully grown
deciduous teeth. Eruption and growth of teeth in cubs
had considerable individual differences. Erupting se-
quence of the deciduous teeth may be: the canine teeth,
then the premolars and incisors, or ®rst the incisors,
then the canine teeth and premolars.
Olfactory, visual, auditory and gustatory senses
Olfactory sense developed very quickly. When the cub,
Yongliang, was tested using an alcohol tampon near his
nares, he had no reaction until he was 18 days old. At
this time, he started to gnash his jaws when he smelled
the odour of alcohol. About 45 days after birth, Yon-
gliang could distinguish the odour of the keepers from
that of strangers. As a stranger came near, he continu-
ously gnashed his jaws to drive the stranger away.
Giant pandas have acute olfaction but poor vision.
Newborn cubs have tightly closed eyes and had no
reaction to outside light stimuli. About 1 month after
birth, the cubs started to respond to light. Cubs partially
open their eyes 48  10 days after birth. Usually, one eye
263Growth and development of giant panda cubs
Table 1. Birth weight, body and tail length of ®ve Ailuropoda
melanoleuca cubs at birth date in Beijing Zoo
Cubs Litter size Birth weight Body length Tail length
(g) (cm) (cm)
1 Twin 150 12.0 6.0
2 Twin 180 13.5 6.8
3 Twin 170 13.0 6.6
4 Twin 150 12.2 6.1
5 Twin 106 9.8 5.0
0
10
20
30
40
50
60
70
80
120
110
100
90
Body length
Chest circumference
Tail length
Length (cm)
12345678
Age (months)
Fig. 3. Increase in body size of giant panda Ailuropoda
melanoleuca cubs > 8 months after birth in Beijing Zoo.
Table 2. Body measurements of Ailuropoda melanoleuca cubs over their ®rst 8 months
Age (month)
Measurements (cm) 12345678
Body length 35.2  2.7 50.5  2.6 66.7  2.4 74.6  1.3 94.5  2.1 99.6  2.3 103.3  2.6 105.1  3.7
Chest circumference 28.0  1.0 44.3  2.6 48.1  0.7 53.8  0.8 56.8  2.6 62.4  2.8 65.5  3.1 68.0  3.5
Tail length 5.3  0.8 5.6  0.6 6.0  0.6 6.7  0.5 7.5  0.7 7.8  0.6 8.7  0.8 9  0.9

opened ®rst. Cubs fully opened their eyes 56  12 days
after birth. The eyesight of cubs was poor, but it
gradually improved when the cubs were 3 months old.
Auricles of giant panda cubs developed from granule
into oblate at 4±5 days old. Sounds like a clack could
arouse cubs aged 2.5 months, which showed that they
already possessed auditory sensation. Three months
after birth, the auditory sense of the cubs was acute and
they responded to various sorts of sounds.
Gustatory sense of the cubs started at c. 10 days old.
At this time, they could distinguish glucose solution
(5 mg/ml) from a mixed solution of glucose and physio-
logical saline water.
Suckling and feeding behaviours
Cubs spent their time primarily sleeping and suckling
during the ®rst 2 months after birth. Newborn cubs
suckled about six to 12 times per day during the ®rst
2 weeks after birth. The suckling duration ranged from
0.5 to 15 min, sometimes cubs may suckle for up to
30 min. Suckling bouts were reduced to three to four
times per day when the cubs were 2 months old, and
3- to 4-month-old cubs suckled two to three times per
day. Five-month-old cubs only suckled one to two times
per day.
DISCUSSION
Growth rate
Differences between the birth weights of newborn giant
panda cubs were remarkable. Recorded birth weight
varied between 36 and 183.2 g. About 46.4% of the
newborn cubs were heavier than 120 g, and 21.4% were
lighter than 100 g (Hu, 1988). However, we do not
know whether the birth weight of the cubs is related to
the litter size, the length of gestation period, the order of
birth, or the healthy status and age of their mothers.
Cubs grew and developed exponentially during the ®rst
12 months after birth. Since the growth curve for
animals is typically sigmoid (Kirkwood & Mace, 1996),
the growth curve of cubs in the study indicated that
their growth would continue for another period.
Growth rates were different between male and female
cubs older than 3 months. Hu et al. (1985) reported
sexual dimorphism in adult giant pandas with the body
weight of males (117.8  15.2 kg) being generally 10±
20% heavier than that of females (98.8  11.3 kg). Body
length and chest circumference of the cubs increased
quickly after birth, but the relative growth rates of the
tail and feet were slow. With the increase of body size,
the relative length of the tail decreased from c. 14.9% of
the body length in 1-month-old cubs to 8.6% in
8-month-old cubs, which implies that the giant panda
may be the descendant of a long-tailed ancestor.
Body development
Zhong et al. (1994) reported that the teeth formula of
one cub was 3121/3121 = 28 at 1-year-old, and Feng
et al. (1991) reported that the teeth formula of two cubs
was 3122/3122 = 32. At 3±4 years old, they grew
permanent teeth. The teeth formula of an adult giant
panda is 3142/3143 = 42 (Hu et al., 1985; Ma et al.,
1994). Because the ®rst upper and lower premolars are
small, they are often missing in aged giant pandas.
J. Peng ET AL.264
Table 3. Changes of fur colour in Ailuropoda melanoleuca cubs
Date Changes of fur colour
Days 6±7 Skin around the ears, eye sockets and aiguillette slightly blackened
Days 8±9 Black hair appeared on forelimbs; black area around ears and eye sockets enlarged and the black area on
aiguillette became one black strip
Days 10±12 Black hairs appeared on hindlimbs; black area around ears and eye sockets observable; black area around eye
sockets enlarged further and become round, the diameter of the black spot around the eye socket was c.1cm
Day 13 Black hairs appeared on the upper rim of nares and the corner of mouth
Day 16 Black colour thickened and black hairs present in the chest region; black area of eye socket continued to enlarge,
the black area changed from round into rhombic, like that in the adults
Day 18 Black hairs appeared on the neck, fore- and hind-palms
Day 25 Black hairs spread throughout the whole neck and chest; black area around the eye sockets enlarged; new white
hairs grew; margins between skin with black and white hairs were clear
Day 30 Hairs grew longer and fur became compact, but most of the region still unshed
Day 45 Chest and abdomen region covered with compact white hairs
Day 50 Fur colour of the areas below the middle of chest and abdomen reddish brown, the rest areas of the middle chest
and abdomen black with a little dark brown; tip of the tail had a ®stful of black hairs
Table 4. Teeth growing sequence of the giant panda cub, Yongliang, a male born on 14 September in 1992 in Beijing Zoo
Age 60 days 90 days 110 days 130 days 150 days 180 days 1 year
Teeth formula 0.0.0.0 0.0.0.0 0.1.2.0 1.1.3.0 2.1.3.0 2.1.3.0 2.1.3.0
0.0.0.0 0.1.0.0 0.1.2.1 1.1.3.0 2.1.3.0 2.1.3.0 2.1.3.0

Thus, sometimes we ®nd the teeth formula of some
giant pandas is 3132/3143 = 40 or 3132/
3133 = 38. Molars in giant pandas are strong and
resemble those of omnivores.
Giant pandas, bears and raccoons are all sexually
dimorphic (Hu et al., 1985). Males are 8% heavier than
females in red panda Ailurus fulgens, the difference is
17% in raccoon Procyon lotor, 34% in South American
raccoon Nasua nasua, 29±41% in black bear Ursus
thibetanus and 34±38% in brown bear Ursus arctos.
Thus, sexual dimorphism of body weight in the giant
panda is less than that in bears. The giant panda has a
long gestation and the newborn cubs do not open their
eyes at birth, but the gestation period is shorter than
that of bears, and the ratio of cub birth weight to
mother body weight in the giant panda is less than that
of bears. The time of eye opening is later in the giant
panda than in bears. Therefore, the lactation period of
giant panda cubs is longer than that of bears, but
because the giant panda cubs grow and develop quickly
during the lactation period, their body weights are
heavier than those of bears when they start to live
independently.
Breast feeding
Giant panda cubs are late-maturing, according to the
change of fur colour, the growth and development of
teeth, sense organs and limbs. On the ®rst day after
birth, the cubs cried 14 times/h and continuously begged
to be fed. Once they had suckled colostrum and were
cuddled by their mothers, the cubs cried less frequently.
Vocal communication strengthened the relationship
between the cubs and mothers. Giant panda cubs in the
wild do not leave their mothers until 1.5±2 years old,
and they can suckle their mothers' milk even at
8±9 months old (Hu, 1988). During this period, the cubs
learn ®eld survival skills from their mothers. However,
because of the mothers' lack of milk or if the keepers
want the mothers to reproduce again the next spring,
the cubs are often weaned at c. 6 months old. The
growth rate of the arti®cially fed cubs was slightly
higher than that of the cubs fed by their mothers, which
indicated that the substitute milk satis®ed the nutri-
tional needs of the cubs.
The composition of the milk of the giant panda has
been analysed by Lyster (1976), Hudson, Bailey &
John (1984), Liu, Yu, S. Li et al. (1996), Liu, Yu, X. Li
et al. (1997) and Wang (1997). Most of the cubs that
suckled their mothers' milk were healthy, only few fell
ill incidentally during the lactation period (Liu, Xie
et al., 1994). In contrast, the cubs that were fed cow's
milk often fell ill and died (Li et al., 1999). Amino
acids such as threonine, glycine, isoleucine, tyrosine,
lysine and histidine in giant panda colostrum are
signi®cantly higher than that in normal breast milk,
and aspargine, serine, alanine, valine and leucine are
also higher (Liu, Yu, S. Li et al., 1996; Liu, Yu, X. Li
et al., 1997). Therefore, breast milk, especially the
colostrum, cannot be completely replaced by other dairy
products.
Acknowledgements
We acknowledge the ®nancial support of the National
Key Basic Research Project (20000486), Chinese
Academy of Sciences (KSCX2±1±03, C299082, KZ
951-A1-105), and the Natural Science Foundation of
China (No.39725005).
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