Cat and Dog Ownership in Early Life and Infant Development: A Prospective Birth Cohort Study of Japan Environment and Children’s Study

Abstract

Contact with companion animals has been suggested to have important roles in enhancing child development. However, studies focused on child development and pet ownership at a very early age are limited. The purpose of the current study was to investigate child development in relation to pet ownership at an early age in a nationwide prospective birth cohort study: the Japan Environment and Children’s Study. Associations between cat and dog ownership at six months and infant development at 12 months of age were examined in this study. Infant development was assessed using the Ages & Stages QuestionnairesTM (ASQ-3) at 12 months. Among participants of (Japan Environment and Children’s Study) JECS, those with available data of cat and dog ownership at six months and data for the ASQ-3 at 12 months were included (n = 78,868). Having dogs showed higher percentages of pass in all five domains measured by ASQ-3 (communication, gross motor, fine motor, problem-solving, and personal-social) compared to those who did not have dogs. Significantly decreased odds ratios (ORs) of developmental delays were observed in association with having dogs in all fix domains (communication: OR = 0.73, gross motor: OR = 0.86, fine motor: OR = 0.84, problem-solving: OR = 0.90, personal-social: OR = 0.83). This study suggested that early life dog ownership may reduce the risks of child developmental delays.

Full text

International Journal of
Environmental Research
and Public Health
Article
Cat and Dog Ownership in Early Life and Infant
Development: A Prospective Birth Cohort Study of
Japan Environment and Children’s Study
Machiko Minatoya 1,2 , Atsuko Araki 1, Chihiro Miyashita 1, Sachiko Itoh 1,
Sumitaka Kobayashi 1, Keiko Yamazaki 1, Yu Ait Bamai 1, Yasuaki Saijyo 3, Yoshiya Ito 4,
Reiko Kishi 1, * and The Japan Environment and Children’s Study Group †
1Hokkaido University Center for Environmental and Health Sciences, Sapporo 060-0812, Japan;
mminatoya@cehs.hokudai.ac.jp (M.M.); AAraki@cehs.hokudai.ac.jp (A.A.);
miyasita@med.hokudai.ac.jp (C.M.); vzbghjn@den.hokudai.ac.jp (S.I.);
sukobayashi@cehs.hokudai.ac.jp (S.K.); kyamazaki@cehs.hokudai.ac.jp (K.Y.);
u-aitbamai@med.hokudai.ac.jp (Y.A.B.)
2Hokkaido University Faculty of Health Sciences, Sapporo 060-0812, Japan
3Department of Social Medicine, Asahikawa Medical University, Asahikawa 078-8510, Japan;
y-saijo@asahikawa-med.ac.jp
4Faculty of Nursing, Japanese Red Cross Hokkaido College of Nursing, Kitami 090-0011, Japan;
yito@rchokkaido-cn.ac.jp
*Correspondence: rkishi@med.hokudai.ac.jp
†A complete list of the centres and investigators in the Japan Environment and Children’s Study Group is
provided in Appendix A.
Received: 4 December 2019; Accepted: 25 December 2019; Published: 27 December 2019


Abstract:
Contact with companion animals has been suggested to have important roles in enhancing
child development. However, studies focused on child development and pet ownership at a very
early age are limited. The purpose of the current study was to investigate child development in
relation to pet ownership at an early age in a nationwide prospective birth cohort study: the Japan
Environment and Children’s Study. Associations between cat and dog ownership at six months
and infant development at 12 months of age were examined in this study. Infant development was
assessed using the Ages & Stages Questionnaires
TM
(ASQ-3) at 12 months. Among participants of
(Japan Environment and Children’s Study) JECS, those with available data of cat and dog ownership
at six months and data for the ASQ-3 at 12 months were included (n=78,868). Having dogs showed
higher percentages of pass in all five domains measured by ASQ-3 (communication, gross motor, fine
motor, problem-solving, and personal-social) compared to those who did not have dogs. Significantly
decreased odds ratios (ORs) of developmental delays were observed in association with having
dogs in all fix domains (communication: OR =0.73, gross motor: OR =0.86, fine motor: OR =0.84,
problem-solving: OR =0.90, personal-social: OR =0.83). This study suggested that early life dog
ownership may reduce the risks of child developmental delays.
Keywords: pet ownership; child development; birth cohort; ASQ-3
1. Introduction
Childhood is a crucial phase in its contribution to the quality of health, emotional well-being,
learning, and behavior across the life span [
1
]. However, studies of child development have largely
been limited to relationships and interactions with other humans. Studies of the human–animal
interaction have proposed that there are health benefits associated with pet ownership. Pet ownership
Int. J. Environ. Res. Public Health 2020,17, 205; doi:10.3390/ijerph17010205 www.mdpi.com/journal/ijerph

Int. J. Environ. Res. Public Health 2020,17, 205 2 of 11
may provide emotional protection from the stresses and strains of life, and it may encourage a more
active life. Contact with companion animals has been suggested to have important roles in enhancing
child development [
2
,
3
]. The psychological benefits of attachment to pets have been found for a
variety of pet animals, particularly cats [
4
] and dogs [
5
]. Several studies have found a link between
pet ownership, pet attachment, positive attitudes to animals, compassion, empathy, and prosocial
behavior [
6
–
11
]. For many children, companion animals are likely powerful motivators for learning [
12
]
and development [
12
,
13
]. Although pet ownership may have the potential to positively influence child
development, these relationships have received little attention, and a need for research in this area
has been recognized [
12
,
14
]. Especially, studies focused on child development and pet ownership at a
very early age and are limited. This could be partly due to the limited availability of developmental
assessment tools at early ages.
The Ages & Stages Questionnaires
TM
(ASQ-3) is a developmental screening tool widely used
by clinicians, researchers, and intervention programs around the world [
15
]. The ASQ-3 pinpoints
developmental progress in children between the ages of 1 to 66 months. Because this tool is
parent-completed, it provides an efficient and cost-effective method of collecting information regarding
children’s development without the need for trained experts and considered to be an appropriate
method for large prospective cohort study.
The purpose of the current study was to investigate child development in relation to pet ownership
at an early age. In this study, associations between cat and dog ownership at six months and infant
development at 12 months of age were examined using the data from a nationwide prospective birth
cohort study; the Japan Environment and Children’s Study (JECS).
2. Materials and Methods
2.1. Study Design
The JECS is an ongoing nationwide prospective birth cohort study in Japan. JECS study is
conducted at 15 regional centers (Hokkaido, Miyagi, Fukushima, Chiba, Kanagawa, Koshin, Toyama,
Aichi, Kyoto, Osaka, Hyogo, Tottori, Kochi, Fukuoka, and Minami Kyusyu/Okinawa) in Japan. Details
of the JECS project have been described elsewhere [
16
–
18
]. Briefly, pregnant women were recruited
between January 2011 and March 2014. Eligibility criteria for participation included residing in the
study area at the time of recruitment, an expected delivery date after August 2011, comprehension
of the Japanese language, and completing the self-administered questionnaire. In total, 104,065 fetal
records were included in the cohort, including multiple births. The present study used the dataset
jecs-an-20180131, which was released in January 2018 and revised in December 2018.
2.2. Ethical Statement
The JECS protocol was approved by the Ministry of the Environment’s Institutional Review
Board on Epidemiological Studies and by the Ethics Committees of each participating institution
(Appendix A) (ethical project identification code: Kanken19-117). All participants provided informed,
written consent in accordance with the Declaration of Helsinki.
2.3. Study Participants
Of the 104,065 fetal records included in the cohort, 100,144 were live birth. Among participants of
JECS, those with available data of dog and/or cat ownership at six months and data for the ASQ-3 at
12 months were included in this study (n=78,868) (Figure 1).

Int. J. Environ. Res. Public Health 2020,17, 205 3 of 11
Int. J. Environ. Res. Public Health 2020, 17, x FOR PEER REVIEW 3 of 11
Figure 1. Selection of study population.
2.4. Self‐Administered Questionnaires
Details of the self-administered questionnaire in this study have been described previously
[16,17]. Briefly, maternal smoking and drinking at the 2nd/3rd trimesters, maternal and paternal
education, and annual household income during pregnancy were obtained from the M-T2
questionnaire (answered by pregnant women at the 2nd/3rd trimesters); parity was obtained from
the Dr-T1 questionnaire (medical records transcripts at the 1st trimester); and maternal age at
delivery, delivery mode, infant sex, gestational age, and birth weight were obtained from the Dr-0m
questionnaire (medical records transcripts at delivery). Marital status was obtained from the C-6M
questionnaire (answered by mothers at 6 months of postpartum). Duration of breastfeeding, and
maternal mental illness (a Japanese version of the Kessler 6 (K6) scale) were obtained from the C-1Y
questionnaire (answered by mothers at 12 months of postpartum). Information regarding pet
ownership including cats and dogs was obtained from the C-6M questionnaire (answered by mothers
at 6 months of postpartum).
2.5. Outcome Definitions
The ASQ-3 is comprised of 21 age-specific questionnaires for children ages 1 to 66 months to
assess children’s progress in five developmental domains (communication, gross motor, fine motor,
problem-solving, personal-social). Each of the 5 domains has 6 questions, resulting in 30 items for
each age-interval. Each item describes a skill, ability, or behavior to which the parent responds “yes”
(10 points), “sometimes” (5), or “not yet” (0). Parents sometimes omit items when they are unsure of
how to respond or because they have concerns about their child’s performance of the item. The ASQ-
3 scores were not calculated if there were three or more omitted items in a given domain. In the case
of one or two omitted items, an adjusted total domain score was calculated by adding the averaged
item score either once for one omission or twice for two omissions. Children who may potentially be
at-risk for developmental delays at each age-interval are identified by comparing their scores to cutoff
scores. The J-ASQ-3 cutoff scores for each domain were; communication = 15.64, gross motor = 21.49,
fine motor = 34.50, problem-solving = 27.32, personal-social = 21.73 based on the original ASQ-3 [19].
In this study, those who completed the J-ASQ-3 12-months questionnaire at 11 months 0 days through
Figure 1. Selection of study population.
2.4. Self-Administered Questionnaires
Details of the self-administered questionnaire in this study have been described previously [
16
,
17
].
Briefly, maternal smoking and drinking at the 2nd/3rd trimesters, maternal and paternal education, and
annual household income during pregnancy were obtained from the M-T2 questionnaire (answered
by pregnant women at the 2nd/3rd trimesters); parity was obtained from the Dr-T1 questionnaire
(medical records transcripts at the 1st trimester); and maternal age at delivery, delivery mode, infant
sex, gestational age, and birth weight were obtained from the Dr-0m questionnaire (medical records
transcripts at delivery). Marital status was obtained from the C-6M questionnaire (answered by
mothers at 6 months of postpartum). Duration of breastfeeding, and maternal mental illness (a
Japanese version of the Kessler 6 (K6) scale) were obtained from the C-1Y questionnaire (answered by
mothers at 12 months of postpartum). Information regarding pet ownership including cats and dogs
was obtained from the C-6M questionnaire (answered by mothers at 6 months of postpartum).
2.5. Outcome Definitions
The ASQ-3 is comprised of 21 age-specific questionnaires for children ages 1 to 66 months to
assess children’s progress in five developmental domains (communication, gross motor, fine motor,
problem-solving, personal-social). Each of the 5 domains has 6 questions, resulting in 30 items for
each age-interval. Each item describes a skill, ability, or behavior to which the parent responds “yes”
(10 points), “sometimes” (5), or “not yet” (0). Parents sometimes omit items when they are unsure of
how to respond or because they have concerns about their child’s performance of the item. The ASQ-3
scores were not calculated if there were three or more omitted items in a given domain. In the case
of one or two omitted items, an adjusted total domain score was calculated by adding the averaged
item score either once for one omission or twice for two omissions. Children who may potentially
be at-risk for developmental delays at each age-interval are identified by comparing their scores to
cutoffscores. The J-ASQ-3 cutoffscores for each domain were; communication =15.64, gross motor
=21.49, fine motor =34.50, problem-solving =27.32, personal-social =21.73 based on the original
ASQ-3 [
19
]. In this study, those who completed the J-ASQ-3 12-months questionnaire at 11 months

Int. J. Environ. Res. Public Health 2020,17, 205 4 of 11
0 days through 12 months 30 days of ages were strictly included. According to recommend ASQ-3
procedures, adjusted age was used to determine the appropriate ASQ-3 for children who were preterm
(<37 weeks of gestational age).
2.6. Statistical Analyses
ASQ-3 scores of each domain were dichotomized based on the cutoffscores of each domain.
Chi-squared test was used to determine whether there was a significant difference in the frequency
of pass/fail of ASQ-3 scores at 12 months of age each domain in having or not having cats and dogs
at 6 months of age. t-test was used to compare the mean value of maternal age, birth weight, and
gestational age among those who had cats and dogs and those who did not. Logistic regression models
were used to investigate infant developmental delays in association with having cats and dogs. The
models were adjusted for maternal and paternal education, maternal smoking during pregnancy,
annual household income during pregnancy, maternal mental illness, and duration of breastfeeding
based on the previous literature and correlation between these variables and exposure and outcome.
Since there were a small number of missing values for each variable, analyses included only those
without missing variables. p<0.05 was considered as statistically significant. Statistical analyses were
performed using SPSS version 24 (IBM, Armonk, NY, USA).
3. Results
Table 1shows the characteristics of parents and infants included in this study (n=78,868) and
comparison of characteristics between those who had cats and dogs. The pet ownership for cats and
dogs at six months was 6358 (8.1%) and 11,934 (15.1%), respectively. Prevalence of maternal smoking
at the 2nd trimester was higher in those who had cats and dogs. Both maternal and paternal education
levels and annual household income were lower in those who had cats and dogs. Prevalence of possible
maternal mental illness was higher in those who had cats but not dogs. Duration of breastfeeding was
shorter in those who had cats and dogs.
Table 1. Characteristics of participants.
Mean ±SD or n(%)
All Having Cat(s) Having Dog(s)
Parents n=
78,868
Yes (n=
6358)
No (n=
72,510) p-Value Yes (n=
11,934)
No (n=
66,934) p-Value
Maternal age
at delivery
(years)
30.7
±
5.1 30.8
±
5.1 30.7
±
5.1
0.832
30.6
±
5.0 30.8
±
5.1
0.034
Parity
nulliparous 31,078
(39.4)
2503
(39.4)
28,575
(39.4) 0.788 4721
(39.6)
26,357
(39.4) 0.754
multipara 32,986
(41.8)
3720
(58.5)
42,162
(58.1)
6932
(58.1)
38,950
(58.2)
missing
1908 (2.4)
135 (2.1)
1773 (2.4)
281 (2.4)
1627 (2.4)
Maternal
smoking at
2nd trimester
yes
2874 (3.6)
366 (5.7)
2508 (3.5)
<0.001 641 (5.4)
2233 (3.3)
<0.001
no 75,051
(95.2)
5897
(92.7)
69,154
(95.4) <0.001 11,128
(93.2)
63,923
(95.5) <0.001
missing 943 (1.2) 95 (1.5) 848 (1.2) 165 (1.4) 778 (1.2)
Maternal
drinking at
2nd trimester
yes
2134 (2.7)
191 (3.0)
1943 (2.7)
0.123 336 (2.8)
1798 (2.7)
0.415
no 75,789
(96.1)
6086
(95.7)
69,703
(96.1)
11,447
(95.9)
64,342
(96.1)
missing 945 (1.2) 81 (1.3) 864 (1.2) 151 (1.3) 794 (1.2)
Maternal
education
(years)
<13 26,859
(34.1)
2781
(43.7)
24,078
(33.2) <0.001 4905
(41.1)
21,954
(32.8) <0.001
≥13 51,249
(65.0)
3506
(55.1)
47,743
(65.8)
6889
(57.7)
44,360
(66.3)
missing 760 (1.0) 71 (1.1) 689 (1.0) 140 (1.2) 620 (0.9)

Int. J. Environ. Res. Public Health 2020,17, 205 5 of 11
Table 1. Cont.
Mean ±SD or n(%)
All Having Cat(s) Having Dog(s)
Parents n=
78,868
Yes (n=
6358)
No (n=
72,510) p-Value Yes (n=
11,934)
No (n=
66,934) p-Value
Paternal
education
(years)
<13 33,115
(42.0)
3220
(50.6)
29,895
(41.2) <0.001 5940
(49.8)
27,175
(40.6) <0.001
≥13 44,570
(56.5)
3003
(47.2)
41,567
(57.3)
5750
(48.2)
38,820
(58.0)
missing
1183 (1.5)
135 (2.1)
1048 (1.4)
244 (2.0) 939 (1.4)
Annual
household
income at 2nd
trimester
<428,699
(36.4)
2581
(40.6)
26,118
(36.0) <0.001 4440
(37.2)
24,259
(36.2) <0.001
≥444,361
(56.2)
3115
(49.0)
41,246
(56.9)
6205
(52.0)
38,156
(57.0)
missing
5808 (7.4) 662 (10.4) 5146 (7.1)
1289
(10.8)
4519 (6.8)
Marital status
married 74,783
(94.8)
5952
(93.6)
68,831
(94.9) <0.001 11,167
(93.6)
63,616
(95.0) <0.001
divorced/
bereavement 529 (0.1) 72 (1.1) 457 (0.6) 149 (1.2) 380 (0.6)
missing
3556 (4.5)
334 (5.3)
3222 (4.4)
618 (5.2)
2938 (4.4)
Maternal
possible
mental illness
yes (K6
≥
13)
2036 (2.6)
234 (3.4)
1802 (2.5)
<0.001 328 (2.7)
1708 (2.6)
0.205
no (K6 <13) 76,156
(96.6)
6067
(95.4)
70,089
(96.7)
11,493
(96.3)
64,663
(96.6)
missing 676 (0.8) 57 (0.9) 619 (0.9) 113 (0.9) 563 (0.8)
Infant
Sex
male 40,274
(51.1)
3255
(51.2)
37,019
(51.1) 0.721 6095
(51.1)
34,179
(51.1) 0.994
female 38,572
(48.9)
3100
(48.8)
35,472
(48.9)
5835
(48.9)
32,737
(48.9)
missing 22 (0.0) 3 (0.0) 19 (0.0) 4 (0.0) 18 (0.0)
Birth
weight (g)
3041 ±
384
3037 ±
383
3041 ±
384 0.428 3041 ±
386
3041 ±
383 0.926
Gestational
age (weeks)
39.4
±
1.2 39.4
±
1.2 39.4
±
1.3
0.003
39.4
±
1.2 39.4
±
1.3
0.001
Delivery
mode
vaginal 64,007
(81.2)
5157
(81.1)
58,850
(81.2) 0.796 9575
(80.2)
54,432
(81.3) 0.003
cesarean 14,665
(18.6)
1191
(18.7)
13,474
(18.6)
2335
(19.6)
12,330
(18.4)
missing 196 (0.2) 10 (0.2) 186 (0.3) 24 (0.2) 172 (0.3)
Duration of
breastfeeding
(months)
0
1978 (2.5)
205 (3.2)
1773 (2.4)
<0.001 346 (2.9)
1632 (2.4)
<0.001
1–6 16,582
(21.0)
1646
(25.9)
14,936
(20.6)
3000
(25.1)
13,582
(20.3)
7–12 60,308
(76.5)
4507
(70.9)
55,801
(77.0)
8588
(72.0)
51,720
(77.3)
Missing data: n(%), maternal age: n=93 (0.1), birth weight: n=41 (0.05). Chi-square test or t-test.
Table 2shows the distribution of the ASQ-3 12-months questionnaire scores in association
with having cats and dogs at six months of age. The mean scores of each domain were 37.68 for
communication, 42.78 for gross motor, 48.21 for fine motor, 42.35 for problem-solving, and 37.03
for personal-social, respectively. Numbers of infants who failed each domain were 5633 (7.1%) for
communication, 11,368 (14.3%) for gross motor, 8133 (10.2%) for fine motor, 12,505 (15.7%) for problem-
solving, 13,755 (17.3%) for personal-social. Those who had cats showed higher percentages (83.7%) of
pass in the personal-social domain compared to those who did not have cats (82.5%). Having dogs
showed higher percentages of pass in all five domains measured by ASQ-3 compared to those who did
not have dogs.

Int. J. Environ. Res. Public Health 2020,17, 205 6 of 11
Table 2.
Distribution of the ASQ-3 12-months questionnaire scores in association with having a cat and
dog at six months of age.
All Having Cat(s) Having Dog(s)
ASQ Subscale CutoffYes No p-Value Yes No p-Value
Communication
15.64
Mean ±SD
37.68
±
13.43
Pass 73,216 (92.8) 5897
(92.8)
67,319
(92.9) 0.745 11,300
(94.7)
61,916
(92.6) <0.001
Fail 5601 (7.1) 458 (7.2) 5143
(7.1)
630
(5.3)
4971
(7.4)
Missing 51 (0.0)
Gross motor 21.49
Mean ±SD
42.78
±
17.55
Pass 67,556 (85.7) 5486
(86.3)
62,070
(85.6) 0.138 10,414
(87.3)
57,142
(85.4) <0.001
Fail 11,271 (14.3) 869
(13.7)
10,402
(14.4)
1511
(12.7)
9760
(14.6)
Missing 41 (0.0)
Fine motor 34.50
Mean ±SD
48.21
±
11.63
Pass 70,729 (89.7) 5729
(90.2)
65,000
(89.7) 0.236 10,840
(90.9)
59,889
(89.6) <0.001
Fail 8056 (10.2) 622 (9.8) 7434
(10.3)
1079
(9.1)
6977
(10.4)
Missing 83 (0.1)
Problem-
solving 27.32
Mean ±SD
42.35
±
13.61
Pass 66,317 (84.1) 5346
(84.3)
60,971
(84.2) 0.965 10,158
(85.3)
56,159
(84.1) 0.001
Fail 12,398 (15.7) 998
(15.7)
11,400
(15.8)
1754
(14.7)
10,644
(15.9)
Missing 153 (0.2)
Personal- social
21.73
Mean ±SD
37.03
±
14.57
Pass 64,927 (82.3) 5303
(83.7)
59,624
(82.5) 0.018 10,107
(84.9)
54,820
(82.2) <0.001
Fail 13,651 (17.3) 1032
(16.3)
12,619
(17.5)
1791
(15.1)
11,860
(17.8)
Missing 290 (0.4)
n(%). Chi-square test.
Table 3shows infant developmental delays at 12 months of age in association with having cats
and dogs at six months of postpartum. There was no significant association between having a cat
and infant developmental delays of any domains. Contrary, significantly decreased odds ratios (ORs)
were observed in association with having a dog in all five domains. ORs and 95% confidence intervals
(CIs) for each domain were 0.73 (0.67, 0.80) for communication, 0.86 (0.81, 0.92) for gross motor, 0.84
(0.78, 0.90) for fine motor, 0.90 (0.85, 0.96) for problem-solving, 0.83 (0.79, 0.88) for personal-social,
respectively. Further analysis of three groups (only cat ownership, only dog ownership, and both cat
and dog ownership) were conducted, and the results are shown in supplemental Table S3.
Table 3.
Infant development delays at 12 months of age in association with cat and dog ownership at
6 months of age.
OR (95% CI)
Cat Ownership Dog Ownership
Communication 0.94 (0.85, 1.04) 0.73 (0.67, 0.80) **
Gross motor 1.06 (0.98, 1.15) 0.86 (0.81, 0.92) **
Fine motor 1.07 (0.98, 1.18) 0.84 (0.78, 0.90) **
Problem solving 1.02 (0.95, 1.10) 0.90 (0.85, 0.96) *
Personal-social 1.07 (0.98, 1.16) +0.83 (0.79, 0.88) **
Adjusted for maternal and paternal education, maternal smoke during pregnancy, annual household income during
pregnancy, maternal mental illness (K6), duration of breastfeeding. +p<0.10, * p<0.05, ** p<0.001.

Int. J. Environ. Res. Public Health 2020,17, 205 7 of 11
4. Discussion
In this study, we found that having dogs at six months was associated with decreased risks of
infant showing developmental delays at 12 months in five domains of the ASQ-3. However, the
same was not observed among those who had cats. This was the first report on early childhood pet
ownership and child development based on the large-scale prospective birth cohort study data.
The mean scores of the ASQ-3 in this study were relatively lower compared to the recent cohort
study (n=318) as well as US national data [
20
]. The mean scores were also lower compared to the
original scores from the ASQ manual. As it was discussed in the recent literature from Japan, for
the questionnaires for younger children, the scores tended to be lower for the J-ASQ-3 [
21
]. This is
consistent with other developmental assessment tools that showed that Japanese children generally
develop slower than American children until about two years of age [22].
The ownership of cats and dogs in this study was 8.0% and 15.0%, respectively, and this is
comparable to the data from Japan Pet Food Association that reported the prevalence of cat and dog
ownership in Japan was 9.78% and 12.64%, respectively, in 2018 [
23
]. In this study, socio-demographic
characteristics of participants with cats or dogs were less educated parents and less household income,
and maternal age at delivery was significantly younger, which was similar to previous studies [
24
,
25
].
In general, higher parental education and parental social class, and the younger the mother was at
delivery, were related to less pet ownerships. This was only found in dog ownership but not in
cat ownership.
Our findings on pet ownership and child development are in line with findings from other
studies. A systematic review found evidence for an association between pet ownership and a wide
range of emotional health benefits, such as self-esteem and reduced depression from childhood
pet ownership [
26
]. A recent study from Japan suggested that pet ownership in toddlerhood may
contribute to the development of emotional expression of children [
24
]. The same study found that the
prevalence of children with poor emotional expression were in the protective direction for owning
dogs; contrary, the direction was opposite for cat ownership [
24
]. Infants could learn and develop skills
of expression from interacting with their dogs and result in a lower risk of having communication
and personal-social problems. Interaction with dogs may potentially help infants to have better gross
and fine motor development. For example, a study of dog-assisted therapies and activities in the
rehabilitation of children with cerebral palsy and physical and mental disabilities reported that the
children improved their abilities to use their bodies according to their capabilities [
27
]. Another study
showed that the presence of a therapy dog would affect the performance of a set of gross motor skill
tasks for a mixed group of language-impaired and typical preschool children [
28
]. Children in these
studies were older than those in the present study; however, these findings may be an indication of
how beneficial interacting with dogs can be for the motor development of children. The previous
studies suggested that early exposure to pets may contribute to child cognitive development [
29
] and
may facilitate language acquisition and potentially enhance verbal skills in children [
30
]. The presence
of animals has been shown to elicit immediate positive effects in testing situations of cognition, such as
memory, categorization, and attention [
28
,
31
–
35
]. Problem-solving assessed in this study is related to
cognitive function. Together with the previous studies, findings from this study suggested that the
presence of dogs at home may contribute to child cognitive development even at a younger age.
Literature included in the systematic review investigated various kind pets, including birds, fish,
horses, and so on; however, the evidence for the impact of pets on child development was mostly
found only with dogs [
26
]. It has been reported that children with pet dogs scored the highest on
attachment [
36
]. Dogs are also more likely to read and adopt their behavior in response to human
emotional signals [
37
]. These may explain why only ownership of dogs showed a significant decreased
risk of children to have developmental problems. In addition, a study suggested that pet ownership
may be associated with increased social skills, and the positive effect was only found in association
with dog ownerships [
38
]. Research over the past 30 years [
39
] and a systematic review [
40
] indicated

Int. J. Environ. Res. Public Health 2020,17, 205 8 of 11
that dogs may offer physiological, emotional, social, physical support, and beneficial effect on a number
of behavioral processes for children.
Although the ownership of pets showed benefits, including better child development, certain
negative consequences, such as zoonotic infections [
41
], allergy and asthma [
42
], bites and other
injuries [
43
], and the psychological and emotional costs due to loss of pet [
44
] have been noted.
In addition, children are at a greater risk of animal bites from a household pet [
45
,
46
], and children
under five years of age are most at risk of serious injury [47,48].
The strengths of this study are that we used a dataset of large sample size, longitudinal design,
and included a variety of different factors. Health influence in association with pet ownership has
been discussed in case-control studies and cross-sectional studies [
26
,
49
]; however, these previous
studies had limitations in study designs and sample size. In addition, some of the studies did not
consider confounding factors. The current study was the first study to investigate child development
in association with early life pet ownership in a prospective birth cohort study. The characteristics of
parents and infants included in this study were compared to the whole cohort profile data and found
to be similar to the original cohort population [
16
]. However, a comparison between the current study
population (n=78,868) and those who were excluded from the current study due to no data of pet
ownership (n=860) found some significant differences (Supplemental Tables S1 and S2). Percentage of
maternal smoking was higher, and both maternal and paternal education levels and annual family
income were lower among those who were excluded. These characteristics were also common among
those who had cats and dogs (Table 1). This may indicate that the prevalence of pet ownership was
possibly higher among those who were excluded. The mean ASQ-3 scores were higher among those
who were excluded in all domains, which may indicate that less developmentally delayed children
were in this group. These differences in characteristics may impact the findings from this study;
however, the number of those excluded was small (1.1%); thus, the impact is also small even if it existed.
Some limitations of this study should be noted. First, the child developmental delays were
assessed by a parental report. Even though the ASQ-3 is one of the most widely used screening
tools for early childhood development, misclassification may have occurred. We have controlled for
possible maternal mental illness based on the validated Japanese version of the K6 score [
50
] at 12
months postpartum as ASQ-3 scores may have been influenced by maternal mental problems. Second,
the current study only investigated cat and dog ownerships but no other pets. Additionally, it is
important to recognize that pet attachment may be more important in exerting potential health effects
than pet ownership [
51
]. In this study, we could only examine the association between pet ownership
and child development. For further studies, assessment of pet attachment should be considered.
In addition to self-reported questionnaires, observational and behavioral methods would ensure the
accuracy of findings. Third, other important confounding factors, such as the quality of children’s
home environments, needed to be considered because children’s home environment has been linked
with both the concurrent and longitudinal cognitive development of children [
30
,
52
]. The current
study did not control for these confounding factors, which may possibly mask the true association
between dog ownership and infant development.
5. Conclusions
This study suggested that having dogs in early life may possibly reduce the risks of children
to have developmental delays. Further longitudinal follow-up studies are necessary to elucidate
associations between early life pet ownership and child development.
Supplementary Materials:
The following are available online at http://www.mdpi.com/1660-4601/17/1/205/s1,
Table S1: Comparison between the current study population and those who excluded from the current study due
to no data of pet ownership. Table S2: Comparison of ASQ-3 scores between the current study population and
those who excluded from the current study due to no data on pet ownership. Table S3: Infant development delays
at 12 months of age in association with cat and dog ownership at 6 months of age.

Int. J. Environ. Res. Public Health 2020,17, 205 9 of 11
Author Contributions:
Conceptualization, M.M. and R.K.; methodology, M.M.; investigation, M.M.; data curation,
M.M.; writing—original draft preparation, M.M.; writing—review and editing, A.A., C.M., S.I., S.K., K.Y., Y.A.B.,
Y.S., Y.I., R.K., The Japan Environment and Children’s Study Group; visualization, M.M.; supervision, R.K.; project
administration, R.K. All authors have read and agreed to the published version of the manuscript.
Funding:
The Japan Environment and Children’s Study is funded by the operating budget of the Ministry of the
Environment, Japan. The findings and conclusions of this article are solely the responsibility of the authors and do
not represent the official views of the Ministry of the Environment of the Japanese government.
Acknowledgments:
We thank the participants of all mothers and their children who participated in the JECS. We
wish to express our sincere appreciation to the collaborating hospitals and clinics. We also express our gratitude to
all the JECS staffmembers in Hokkaido, Miyagi, Fukushima, Chiba, Kanagawa, Koshin, Toyama, Aichi, Kyoto,
Osaka, Hyogo, Tottori, Kochi, Fukuoka, and South-Kyushu and Okinawa regional centers and national center for
JECS, and the Medical Support Center.
Conflicts of Interest: The authors declare no conflict of interest.
Appendix A
Members of the Japan Environment and Children’s Study (JECS) Group 2019; Michihiro Kamijima
(principal investigator, Nagoya City University, Nagoya, Japan), Shin Yamazaki (National Institute
for Environmental Studies, Tsukuba, Japan), Yukihiro Ohya (National Center for Child Health and
Development, Tokyo, Japan), Reiko Kishi (Hokkaido University, Sapporo, Japan), Nobuo Yaegashi
(Tohoku University, Sendai, Japan), Koichi Hashimoto (Fukushima Medical University, Fukushima,
Japan), Chisato Mori (Chiba University, Chiba, Japan), Shuichi Ito (Yokohama City University,
Yokohama, Japan), Zentaro Yamagata (University of Yamanashi, Chuo, Japan), Hidekuni Inadera
(University of Toyama, Toyama, Japan), Takeo Nakayama (Kyoto University, Kyoto, Japan), Hiroyasu
Iso (Osaka University, Suita, Japan), Masayuki Shima (Hyogo College of Medicine, Nishinomiya,
Japan), Youichi Kurozawa (Tottori University, Yonago, Japan), Narufumi Suganuma (Kochi University,
Nankoku, Japan), Koichi Kusuhara (University of Occupational and Environmental Health, Kitakyushu,
Japan), and Takahiko Katoh (Kumamoto University, Kumamoto, Japan).
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