Estimating the life expectancy of companion dogs in Japan using pet cemetery data

Abstract

The life expectancy provides valuable information about population health. The life expectancies were evaluated in 12,039 dogs which were buried or cremated during January 2012 to March 2015. The data of dogs were collected at the eight animal cemeteries in Tokyo. The overall life expectancy of dogs was 13.7 (95% confidence interval (CI): 13.7-13.8) years. The probability of death was high in the first year of life, lowest in the fourth year, and increased exponentially after four years of age like Gompertz curve in semilog graph. The life expectancy of companion dogs in Tokyo has increased 1.67 fold from 8.6 years to 13.7 years over the past three decades. Canine crossbreed life expectancy (15.1 years, 95% CI 14.9-15.3) was significantly greater than pure breed life expectancy (13.6 years, 95%CI 13.5-13.7, P-value <0.001). The life expectancy for male and for female dogs were 13.6 (95% CI: 13.5-13.7) and 13.5 (95% CI: 13.4-13.6) years, respectively, with no significant difference (P=0.097). In terms of the median age of death and life expectancy for major breeds, Shiba had the highest median age of death (15.7 years), life expectancy (15.5 years) and French Bulldog had the lowest median age of death (10.2 years), life expectancy (10.2 years). When considering life expectancy alone, these results suggest that the health of companion dogs in Japan has significantly improved over the past 30 years.

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*Correspondence to: Inoue, M.: kuro_felis_catus@me.com
©2018 The Japanese Society of Veterinary Science
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (by-nc-nd)
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FULL PAPER
Internal Medicine
Estimating the life expectancy of companion
dogs in Japan using pet cemetery data
Mai INOUE1)*, Nigel C. L. KWAN1) and Katsuaki SUGIURA1)
1)Department of Global Agricultural Sciences, Graduate School of Agricultural and Life Sciences, The University
of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
ABSTRACT. The life expectancy provides valuable information about population health. The
life expectancies were evaluated in 12,039 dogs which were buried or cremated during January
2012 to March 2015. The data of dogs were collected at the eight animal cemeteries in Tokyo.
The overall life expectancy of dogs was 13.7 (95% condence interval (CI): 13.7–13.8) years. The
probability of death was high in the rst year of life, lowest in the fourth year, and increased
exponentially after four years of age like Gompertz curve in semilog graph. The life expectancy of
companion dogs in Tokyo has increased 1.67 fold from 8.6 years to 13.7 years over the past three
decades. Canine crossbreed life expectancy (15.1 years, 95% CI 14.9–15.3) was signicantly greater
than pure breed life expectancy (13.6 years, 95%CI 13.5–13.7, P-value <0.001). The life expectancy
for male and for female dogs were 13.6 (95% CI: 13.5–13.7) and 13.5 (95% CI: 13.4–13.6) years,
respectively, with no signicant dierence (P=0.097). In terms of the median age of death and
life expectancy for major breeds, Shiba had the highest median age of death (15.7 years), life
expectancy (15.5 years) and French Bulldog had the lowest median age of death (10.2 years), life
expectancy (10.2 years). When considering life expectancy alone, these results suggest that the
health of companion dogs in Japan has signicantly improved over the past 30 years.
KEY WORDS: dog, Japan, life expectancy, pet cemetery data
Dogs are the most popular companion animal in Japan with a population estimated to be 9.9 million in October 2016, and with
14.2% of households owning one or more dogs as companion animals [9]. An increasing number of dogs in Japan apparently enjoy
improved health than hitherto partly due to the use of commercial pet food and partly to veterinary medical care [11]. As a result,
their life expectancy is expected to have been extended in recent years.
The estimate of life expectancy provides valuable information about the health and nutritional status of companion animals in a
specic group. Although there have been many studies estimating the longevity of dogs, most of these studies used the median age
as indicator of longevity [14, 16], due to the sample sizes used not being large enough to construct a life table. A relatively large
sample of dying dogs is needed to construct a life table, reecting the ages of all dying individual dogs, and thereby to estimate
the average life expectancy by age, sex and breed. Life table is dened as a valuable analytical tool to summarize the mortality
experience of the current population and to study longevity [1].
There are two principal forms of the life table: the cohort (or generation) life table and the current life table. The cohort life table
records the actual mortality experience of a particular group of individuals (the cohort) over its entire lifetime. The current life
table gives a cross-sectional view of the mortality and survival experience of a population during a current year and is dependent
on the age-specic death rates prevailing in the year for which it is constructed [1].
Previously, Hayashidani et al. [6] conducted a study to estimate the life expectancy of dogs in Japan using pet cemetery data
from 1981 to 1982, constructed a cohort life table and estimated the life expectancy of dogs to be 8.3 years at birth (age zero)
and 8.6 years at one year old (age one). Inoue et al. [7] constructed a current life table for insured dogs from 2010 to 2011 and
estimated their life expectancy to be 13.7 years at birth. The results of these studies were not comparable because of the dierent
types of life table and data source. The data based on the cemeteries was biased in the region (only in Tokyo) and the data based on
the insurance was biased in age, breed, urban/rural areas and accessibility to medical care.
The purpose of this study was to estimate the life expectancy of companion dogs in Japan by constructing a cohort life table and
median, minimum and maximum age at death using data collected at animal cemeteries in Tokyo, and to compare the longevity
with previous study in Japan. We also calculated the proportional mortality by month and season.
Received: 11 July 2017
Accepted: 14 May 2018
Published online in J-STAGE:
24 May 2018
J. Vet. Med. Sci.
80(7): 1153 –115 8, 2018
do i: 10.1292 /jv ms.17- 038 4

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MATERIALS AND METHODS
Data collection
Data on 12,039 dogs which were buried or cremated during January 2012 to March 2015 were collected at the eight animal
cemeteries which were members of the Tokyo Society of Pet Cemeteries (under the auspice of Tokyo Metropolitan Veterinary
Medical Association). Information on the dog’s sex, breed, age (in years and in months) and month of death were collected by face-
to-face interview with the owner or the person who brought the dog to the cemetery using a standardized questionnaire. Data was
not available on whether or not the dogs were naturally deceased or euthanised. In cases where the owner or the person was unable
to remember the dog’s exact age in months and only able to remember the age rounded down in years, a random number between 0
and 11 was generated and added to the age stated to compute the dog’s age in months (n=4,230).
Construction of life table
We assumed that the 12,039 dogs included in the current study as a cohort and constructed a cohort life table using the method
described in Chiang [1]. In constructing the life table, we used an age interval of one year (x, x+1). The basic variables involved
in a cohort life table are lx, the number living at age x and dx, the number dying in the age interval (x, x+1). We calculated the
probability of a dog dying in age interval (x, x+1), as a proportion of dogs that died during this age interval over the dogs alive
at age x. . We calculated the fraction of last year of life for age x, áx as the average of the fraction of last year of life for
dogs that had died during the interval (x, x+1). We calculated the number of years lived by the total cohort in interval (x, x+1),
Lx = (lx–dx)+ax×dx. We calculated total number of years lived beyond age x, Tx as the sum of the number of years lived in each
age interval beginning with age x. Tx = Lx + Lx+1 + ··· + Lw, x =0, 1, …, w. We constructed a life table using these vaiables, in
accordance with the method described by Chiang [1]. The life expectancy at age was calculated, as the number of years, on the
average, yet to be lived by a dog of age x. . We constructed a life table for all breeds and sexes combined and for pure and
cross breeds and for dierent sexes. We calculated the variance (S) and standard error (S.E.) of life expectancy using the method
described by Chiang [1]. The signicance of dierence (di) of life expectancy between dierent breed groups and sexes was also
tested. The statistics for Z test was calculated by , where and were life expectancy at age 0 of dierent
breed and sexes groups, and S.E. (di.) was dened as (Chiang, 1984). The threshold of
signicance was P-value=0.05. The 95% condence intervals were calculated by .
We also calculated the life expectancy at age 0 for 21 dog breeds whose sample size (n) was larger than 100, as well as their
median, minimum and maximum age of death.
Proportional mortality by month and season
The proportional mortality by month was calculated as a proportion of dogs that died in the respective months over the total
number of dogs that died. Likewise, the proportional mortality by season was calculated as a proportion of dogs that died in the
respective seasons (summer: April to September; winter: October to March). The dierences were tested using χ2 test for a single
comparison. The 95% condence intervals were calculated using the formula
95 196%CI=±.ˆp
ˆp (1−ˆp )
N
where is the extimated
proportion and n is the sample size for the respective months or seasons.
For all statistical analyses, Excel 14.0 (Microsoft Corporation) was utilized.
RESULTS
Table 1 shows the cohort life table for all breeds and sexes combined. The probability of death was 0.0099 in the rst year of
life, and decreased to its lowest in the fourth year of life, and increased like a Gompertz curve after four years old in semilog graph
(Fig. 1). The life expectancy at age zero, or the average lifespan was 13.7 (95% Condence Interval (CI): 13.7–13.8) years. The
cross breed had a signicantly longer life expectancy (15.1 years, 95% CI: 14.9–15.3) than pure breed (13.6 years, 95%CI:13.5–
13.7) (z-test, P-value <0.001, Table 2). The life expectancy for male and for female dogs was 13.6 (95%CI:13.5–13.7) and 13.5
(95%CI: 13.4–13.6) years, respectively, with no signicant dierence (z-test, P-value=0.097, Table 2).
The median age of death was 14.0 years for all breeds and sexes combined. Shiba had the highest expectation of life at age 0
(15.5 years) and median age of death (15.7 years), and French Bulldog had the lowest expectation of life at age 0 (10.2 years) and
median age of death (10.2 years) (Table 3).
In terms of the month of death, 10.3% of the dogs that died in this study died in February, 7.2% of the dogs died in June, 11.1%
of dogs in December (Fig. 2). The proportion of dogs that died in the winter season (October to March) was higher than that of
dogs that died in summer season (April to September) with signicant dierence (χ2, P<0.05).

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DISCUSSION
We constructed a cohort life table using animal cemetery records in Tokyo, aiming to provide scientic information on the
average life expectancy of companion dogs in Japan. The average number of registered companion dogs in Tokyo in 2012–2015
under the Rabies Prevention Law was 516,750 [15]. The sample size of the dogs subjected to the current study represented 2.3%
(=12,039/516,750) of the registered companion dog population in Tokyo. To examine how much we can generalize from our data,
we compared the dog population brought to the cemeteries with the general dog population in Japan. We examined if the dog
population used in our study is representative of the general dog population in terms of breed. According to the result of a survey
conducted by the Japan Pet Food Association in 2015, cross breed dogs represent 17.5% of the dog population in Japan [9], while
the cross breed dogs represented 9.3% of the dog population used in our study. This indicates that the pure breed dogs might be
over-represented in our study, and consequently the overall life expectancy might have been underestimated.
In our study, we estimated an overall life expectancy of 13.7 at age zero, while a previous study by Hayashidani et al. [6]
estimated an overall life expectancy of 8.3 and 8.6 years at ages zero and one respectively, by constructing a cohort life table
using data of 4,915 dogs brought to a cemetery in Tokyo. Their results showed that the life expectancy at age zero (8.3 years) was
lower than that at age one (8.6 years) with the probability of death at age zero (0.15), being higher than that at age one (0.06).
This phenomenon, which was not observed in our study, might be attributed to sampling bias as a result of owners’ behavior who
seldom buried their dogs at young ages in those years [6]. Moreover, in their study the probability of death at the ages 10, 15
and 20 was relatively high, indicating that the owners most probably rounded up and down the dogs ages as they got older [6].
Despite these dierences in data quality and presence of biases in our and their studies, the life expectancy of companion dogs in
Tokyo has increased 1.67 fold from 8.6 years to 13.7 years over the past three decades. The leading causes of death for companion
dogs in the early 1980s were infectious diseases such as heartworm disease, gastrointestinal nematodiasis and canine distemper,
hit-by-car accident and malnutrition [18]. The increased provision of veterinary care and the assumed improved nutrition as a
result of increasing use of well-balanced commercial pet food as well as promotion of animal welfare among Japanese people in
recent years might have resulted in the extended life expectancy in recent years. In the other study in the UK, the median estimate
of 11.1 years from dogs insured and attending dog shows in 1999 [14], the median longevity for dogs of 12.0 years from primary
veterinary hospital data in 2013 has reported [16]. These studies showed the longevity of dogs has extended considerably in these
countries.
Table 1. Cohort life table for companion dogs for all breeds and sexes combined
Age interval
in years
Probability of
dying in interval
(x,x+1)
Number
living at
age x
Number dying
in interval
(x,x+1)
Fraction of
last year of
life
Number of years
lived in interval
(x,x+1)
Total number
of years lived
beyond age x
Expectation
of life at
age x 95% Condence
Interval of êx
x to x+1 lxdxáxLxTxêx
0–1 0.0099 12,039 119 0.3 11,953 165,225 13.7 13.7 – 13.8
1–2 0.0083 11,920 99 0.6 11,876 153,272 12.9 12.8 – 12.9
2–3 0.0066 11,821 78 0.4 11,775 141,396 12.0 11.9 – 12.0
3–4 0.0062 11,743 73 0.5 11,706 129,620 11.0 11.0 – 11.1
4–5 0.0059 11,670 69 0.5 11,633 117,914 10.1 10.0 – 10.2
5–6 0.0092 11,601 107 0.5 11,548 106,281 9.2 9.1 – 9.2
6–7 0.0124 11,494 143 0.4 11,412 94,732 8.2 8.2 – 8.3
7–8 0.0157 11,351 178 0.5 11,257 83,320 7.3 7.3 – 7.4
8–9 0.0286 11,173 319 0.5 11,006 72,063 6.4 6.4 – 6.5
9–10 0.0404 10,854 438 0.5 10,617 61,057 5.6 5.6 – 5.7
10–11 0.0611 10,416 636 0.4 10,058 50,440 4.8 4.8 – 4.9
11–12 0.0818 9,780 800 0.5 9,347 40,382 4.1 4.1 – 4.2
12–13 0.1219 8,980 1,095 0.5 8,390 31,035 3.5 3.4 – 3.5
13–14 0.1612 7,885 1,271 0.4 7,184 22,644 2.9 2.8 – 2.9
14–15 0.2292 6,614 1,516 0.5 5,797 15,461 2.3 2.3 – 2.4
15–16 0.3166 5,098 1,614 0.5 4,249 9,664 1.9 1.9 – 1.9
16–17 0.4038 3,484 1,407 0.5 2,732 5,415 1.6 1.5 – 1.6
17–18 0.4872 2,077 1,012 0.5 1,545 2,683 1.3 1.3 – 1.3
18–19 0.6225 1,065 663 0.5 724 1,137 1.1 1.0 – 1.1
19–20 0.6741 402 271 0.5 272 414 1.0 0.9 – 1.1
20–21 0.6336 131 83 0.6 94 141 1.1 0.9 – 1.2
21–22 0.7292 48 35 0.5 29 47 1.0 0.7 – 1.2
22–23 0.5385 13 7 0.9 12 18 1.4 1.0 – 1.8
23–24 0.5000 6 3 0.2 4 6 1.0 0.4 – 1.5
24–25 0.6667 3 2 0.5 2 2 0.8 0.4 – 1.2
25 1.0000 1 1 0.3 0 0 0.3 0 – 0.8
q
x
ˆ

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The comparison the life expectancy of common breeds was not enough only using expectation of life at age 0, because the
number of each breeds were small to construction life table. So the median ages of death ware used to evaluate longevity with
expectation of life at age 0. The result of our study was not consistent with the results of previous studies, which reported that
breeds with smaller body mass have greater longevity [12, 13, 17]. Among the eleven dog breeds which had an older expectation
of life age at 0 than all breeds combined (13.7 years), there were four medium breeds (Shiba, cross breed with body weight >10
kg, Shetland Sheepdog and Beagle), three small breeds (Miniture Dachshund, Shih Tzu and Papillon), three toy breed (Yorkshire
Terrier, maltese and Pomeranian) and one large breed (Labrador Retriever); while among the ten dog breeds which had a younger
expectation of life age at 0, there were one large breed (Golden Retriever), three medium breeds (American Cocker Spaniel,
Pembroke Welsh Corgi and French Bulldog), four small breeds (Miniature Schnauzer, Cavalier King Charles Spaniel, Pug and
cross breed with body weight <10 kg) and two toy breeds (Chihuahua and Toy Poodle) (Table 3). This suggests that the longevity
of dogs might not be directly related to the size of the breed and highlighted the need to analyze life expectancy at individual breed
level since there could be certain common diseases aecting a particular breed.
Fig. 1. Probability of dying of dogs.
Table 2. Life expectancy of companion dogs by breed and sex
Breed/Sex Number Expectation of
life at age 0
(95% Condence
Interval) P-Value
All 12,039 13.7 (13.7 – 13.8)
Breed
Pure Breed 10,922 13.6 (13.5 – 13.7) <0.00001
Cross Breed 1,117 15.1 (14.9 – 15.3)
Sex
Male 6,189 13.6 (13.5 – 13.7) =0.097
Female 5,850 13.5 (13.4 – 13.6)

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In the present study, Shiba had the oldest age of death (15.7 years) which was even higher than that for cross breeds (BW >10
kg) (15.4 years). According to a recent study using data from insured dogs in Japan [8], the prevalence of dermatological disorders
in Shiba was high (mean annual prevalence is 29%), while the prevalence of life threatening diseases such as neoplasia and
cardiovascular disorders were relatively low. Moreover, French Bulldog, Golden Retriever, Pug, Chihuahua and Cavalier King
Charles Spaniel, which had a relatively low life expectancy based on our results, were all breeds with high risk of neoplasia or
cardiovascular disorders [8]. Since dogs appear to display variation in life expectancy and causes of death across individual breeds
[4, 16], further research on the genetic factors aecting longevity at individual breed level is highly needed.
Recently, the biology of ageing and social factors inuencing longevity have been widely researched [3]. The increasing role
of companion dogs as an animal model for researches in geroscience and life extension science has also been highlighted [5]. In
terms of the reason of larger dog breeds living shorter, it has been hypothesized that they expend relatively more energy to growth
due to slow growth rates and this causes additional base damage to cells as a result of increased oxidative stress [10]. Furthermore,
Table 3. Expectation of life at age 0, median, minimum and maximum age at death of the companion dogs subjected to the analysis
Breeds Number Expectation of
life at age 0
95% Condence
Interval of êx
Age at death (years) Group by
body mass a)
Median Minimum Maximum
Miniature Dachshund 1,578 13.9 13.7 –14.0 13.9 0.0 21.6 Small
Chihuahua 1,079 11.8 11.7– 11.9 11.8 0.0 21.7 To y
Shih Tzu 962 15.0 14.8 – 15.1 14.8 0.1 20.9 Small
Yorkshire Terrier 784 14.3 14.0 – 14.5 14.5 0.0 20.3 To y
Shiba 614 15.5 15.3 – 15.8 15.7 0.0 25.2 Medium
Toy Poodle 560 12.7 12.3 –13.2 13.5 0.0 22.4 Toy
Maltese 437 14.3 13.9–14.6 14.5 0.0 22.8 Toy
Pembroke Welsh Corgi 405 13.5 13.3 – 13.7 13.3 0.5 18.8 Medium
Pomeranian 386 14.0 13.7 – 14.4 14.3 0.2 20.7 To y
Papillon 382 14.4 14.1 – 14.7 14.4 0.5 23.0 Small
Cross breed (BW >10 kg) 368 15.3 15.0–15.6 15.4 0.8 23.9 Medium
Labrador Retriever 328 14.1 13.8 –14.3 14.0 0.6 19.2 Large
Golden Retriever 295 13.1 12.8– 13.4 12.9 0.2 18.0 Large
Miniature Schnauzer 286 13.4 12.9–13.8 13.2 0.1 18.3 Small
Cavalier King Charles Spaniel 251 13.1 12.7–13.4 13.0 0.1 18.5 Small
Shetland Sheepdog 239 14.3 13.9 – 14.6 14.1 0.8 24.1 Medium
Beagle 205 14.8 14.4 – 15.1 14.5 3.8 20.0 Medium
Pug 193 12.8 12.1 – 13.4 12.6 0.2 19.0 Small
Cross breed (BW <10 kg) 182 13.3 12.5–14.0 14.5 0.0 21.2 Small
French Bulldog 151 10.2 9.7– 10.7 10.2 0.1 15.9 Medium
American Cocker Spaniel 139 12.8 12.3 – 13.3 12.8 0.3 17.7 Medium
Total 12,039 13.7 13.7 – 13.8 14.0 0.0 25.2
a) Breeds were classied into ve groups of breeds according to their ideal body weights: toy (<5 kg), small (5–10 kg), medium (10−20 kg), large (20−40
kg) and giant (≥40 kg). Data on the ideal weight of each breed were obtained from the Japan Kennel Club (2013).
Fig. 2. Proportional mortality of dogs by month.

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a study on the lifespan of dogs using Rottweiler as a model revealed that the mortality rates of neoplasia for long-living dogs
were lower than that for young dogs [2], suggesting that long-living dogs might have genetic resistance against life-threatening
diseases. In addition, it has been proposed that companion dogs might have higher risks of neoplasia due to the potential exposure
of the carcinogen also aecting humans [19]. Overall, researches on the lifespan and ageing of dogs will help promote the health
of companion dogs, thus improving the quality of life of dogs’ owners and also providing important information to benet human
health.
Proportional mortality by month of companion dogs obtained in our study showed that dogs had a higher probability of death
during the winter season than summer season. Further studies are needed to identify the risk factors aecting the seasonal mortality.
The current study analyzed the life expectancy of dogs in Japan but not their causes of death. Therefore, further mortality
analyses on the causes of death for individual dog breeds at dierent age intervals are warranted to provide scientic information
that will enhance the quality and length of life for companion dogs.
ACKNOWLEDGMENTS. We would like to thank Tokyo Society of Pet Cemeteries and the Tokyo Veterinary Medical Association
for providing us with data of companion dogs for this study.
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