Discussion between 1968 and 197 The estimates were 14.7
L . Wallin et al. Livestock Production Science 63 2000 275 –289
285 Table 9
Causes of death among warmblood and coldblood horses in the Cavalry Horse Foundation data for geldings G and mares M Cause of death
Warmblood Coldblood
Total number Number
Total number Number
n G
M n
G M
Musculoskeletal system 119
57.2 107
12 13
13.4 6
7 Respiratory system
17 8.2
15 2
2 2.1
2 Digestive system
10 4.8
9 1
6 6.2
4 2
Hoof 7
3.4 6
1 8
8.2 7
1 Nervous system
6 2.9
5 1
22 22.7
14 8
Accidents 5
2.4 3
2 3
3.1 3
Circulatory system 5
2.4 5
0.0 Tumours
3 1.4
3 0.0
Poisoning 1
0.5 1
0.0 Infectious diseases
0.0 1
1.0 1
Eye diseases 1
0.5 1
1 1.0
1 Miscellaneous
5 2.4
4 1
15 15.5
10 5
Unknown 29
13.9 27
2 26
26.8 11
15 Total
208 100.0
185 23
97 100.0
54 43
Table 10
be explained by the fact that mares have a value as
Numbers of deaths attributed to diseases of the musculoskeletal
breeding animals besides riding and competition,
system among warmblood horses in the Cavalry Horse Foundation
which geldings do not. It was shown in the study,
data
that a large proportion of the mares that participated
a
Site of disease injury Number
Percentage
in the RHQT also were used for breeding.
Joints 65
54.6
The brood-mares born between 1965 and 1967
Degenerative joint disease 62
52.0
were included in this study for the purpose of
Osteochondrosis 1
0.8
understanding more about length of life in mares.
Miscellaneous 2
1.7
This group was expected to live many years because
Skeleton 32
26.9
of minimum physical stress, compared with riding
Fractures 13
10.9
and competition horses. It was therefore interesting
Navicular disease 19
16.0
to see that mares, that participated in the RHQT and
b
Tendons 2
1.7
were born between 1968 and 1975, and used for
Undefined lameness 20
16.8
riding as well as breeding, had the same median
Total 119
100.0
length of life as brood-mares 18.3 and 18.6 years,
a
respectively, Table 6.
Percent of horses whose death was attributable due to diseases
There was also close agreement in the median
of the musculoskeletal system.
b
The cause was tendinitis in all cases.
length of life between the warmblood geldings born between 1970 and 1975 from the CHF, and males
that participated in the RHQT and that were born
5. Discussion between 1968 and 1975. The estimates were 14.7
and 13.9 years, respectively Table 6. According to the results from the RHQT data, it is
More than half of the horses had died among both important to estimate the median length of life for
warmblood CHF geldings and stud book brood- each sex separately. A statistically significant differ-
mares at the time of data collection. A calculation of ence of as much as 7.5 years was found in favour of
median length of life based on Tables 3 and 5 gave mares Table 6. The difference between sexes could
values of 14.4 and 17.3 years, respectively. The
286 L
. Wallin et al. Livestock Production Science 63 2000 275 –289
estimates from the survival analyses were 14.7 and veterinary examination of the horses, which gives
18.6, respectively, with a SE of 0.4 Table 6. In the guidelines for the continued training of young
CHF data, all horses could have lived to 14 years, horses. In the early years of the RHOT many
i.e. almost to the median length of life. Therefore, problems related to training were found in horses,
estimates of median length of life, ignoring or taking while such problems most likely have become less
account of censoring, were almost identical. For the frequent in later years Darenius, 1998.
brood-mare data, however, there was censoring from This study also showed that coldblood geldings
an early age, which led to a larger difference from the CHF had 3 years longer median length of
between the two estimates. The conclusion is that life than warmblood geldings. The longer median
even when more than half of the animals have died, length of life may be attributed to the area of use, as
it seems advantageous to use survival analysis if the most of the them were draught horses. The differ-
data are censored. ence between coldblood geldings and mares was
Apart from the difference between sexes, there small, but the material was limited in size. Un-
was also a difference between time periods of birth fortunately, there was no information available on
in the RHQT data. The positive trend in length of whether or not the coldblood mares had been used
life over time seen in Fig. 2 was confirmed by the for breeding.
results from the survival analyses when a birth-year Comparable figures from the literature are rare,
group was introduced into the model as an explanat- and particularly on estimated average life time not
ory variable Table 6. The estimated median length based on insurance data. Comfort 1958, 1959, 1962
of life for mares and males born in the second and used very old data drawn from consecutive periods
third birth-year groups were statistically significantly 1860–1921 of the General Stud Book. He esti-
longer than for those born in the first group Table mated the mean expectation of further life to 17.2
6. The increasing number of horses censored due to years for all 4-year-old thoroughbred mares 1958
the shorter time from birth to censoring time might and 19.5 years for stallions 1959. The median life
have influenced the longer estimated median length times were estimated to 22.1 and 22.2 years, for the
of life in the last two birth-year groups. It should be mares born 1860–1864 and 1875–1880, respectively.
noted that the estimates for the two groups showed Comfort 1962 also studied data on Arabian stud
standard errors which increased in inverse proportion book mares and found the expectation of further life
to the number of animals with a failure time. The at 4 years to be 18.8 years. A study by Langlois
latter should therefore be the dominant part of the 1976 included data of the French stud book, where
data for achieving reliable estimates. the average age at death or culling for thoroughbred
The procedure to account for tied failure times mares and stallions were 14.4 and 16.3 years,
seemed to work satisfactorily. The median length of respectively. Thus, these studies comprising two very
life for mares RHQT was for example on the different time periods gave clearly different results.
average 22.2 years for the 100 replicates with a SD The much lower values found in recent materials
of 0.4. The average had a SE of 0.04 which is much may be due to quite different demands on both the
smaller than the SE of each estimate from
PROC
sport and the breeding stock resulting in a higher
LIFEREG
1.2. Therefore, the introduction of random turnover rate of the mares and stallions selected for
noise was almost totally obliterated by the 100 breeding than previously.
replicates and only the average standard error from Clausen et al. 1990 and Heisele 1995 were
PROC LIFEREG
was used when comparing various both using insurance data, and the estimated average
estimates. ages for dead horses were 10.1 and 12.2 years,
There have been changes over time that may have respectively.
The Swedish
insurance company
influenced the length of life in horses. When training AGRIA Ohlsson, 1990 showed an increase in the
courses became available for owners and their horses average age of dead horses from 8.7 to 10.8 years
¨ during the 1970s information on how to train young
between 1979 and 1988. Koning 1983 also used horses improved considerably. It is important to
insurance data and compared the average age for remember that the RHQT includes a comprehensive
dead horses in her study with a report from
L . Wallin et al. Livestock Production Science 63 2000 275 –289
287
Gutekunst 1977 and found that the average age at of death in a relatively unselected group of dead
death had increased from 9.0 to 10.3 between 1971– horses, mainly of the companion type. In their study,
1974 and 1982 for riding horses. It is interesting to only 16 of the horses were culled due to locomotor
see that there is a positive trend also for the average disorders. Swedish insurance statistics from AGRIA
age for insured dead horses. However, that could 1995 showed that 54 of dead horses were culled
equally well reflect changes in insurance policy. One due to diseases of the musculoskeletal system.
basic problem when studying insurance data is that Statistics from AGRIA included all breeds.
few reports include the initial age when horses were Diseases of the respiratory and digestive systems
insured Heisele, 1995. Lindner and Offeney 1992 also caused death and culling of many horses Tables
also reported that only a small proportion of horses 7 and 9. Again, there was close agreement between
were insured, compared with the total horse popula- the two warmblood groups, 9 and 8, respectively
tion in Germany. The difference between breeds is and 6 and 5, respectively. In the studies by Clausen
also difficult to interpret because of the mixture of et al. 1990 and Heisele 1995 as many as 16–17
breeds in most insurance studies. Insurance policies of the horses had died from diseases of the respirato-
that differ between companies and years are also ry system. In both these studies, 10 of the horses
difficult to consider. It is important that estimates died from diseases of the digestive system, about
from insurance data are interpreted as an average age twice as many as in the present study. Among horses
for dead horses, compensated through their insurance of the companion type, the proportion of horses
policies and not confused with the estimated median dying of respiratory diseases 9 agreed closely
length of life of a given horse population as in this with warmbloods in the present study, but as many
study. as 33 had died of digestive diseases, which was the
Length of life as estimated in this study is a useful predominant cause of death in the study by Baker
measure contributing to the understanding of the and Ellis 1981. Hommerich, 1995 found a variation
state of health in horses. Ricard and Fournet-Hanocq of 7–18 between 1984 and 1994 for diseases of the
1997 used number of years in competition as an respiratory system and 11–18 for diseases of the
indirect indicator of longevity for jumping horses. digestive system. Diseases of the digestive and
Due to the lack of data for analysing causes of death, respiratory systems were also two large pathological
Ricard and Chapuis 1997 suggested that extremely groups 9 and 7, respectively responsible for the
low predicted sire breeding values for longevity in death of many horses, according to the statistics from
sports may reveal a specific pathology. Therefore, AGRIA 1995, but hoof diseases caused even more
these sires and their offspring should be studied in 10 deaths. The differences between studies illus-
more detail. Longevity studies are important if trate the difficulty of making comparisons when the
soundness is to be considered in breeding goals and distribution of the diseases by breed is not clearly
greater effort must be made to find indicators of defined.
longevity in order to ascertain an improvement. Among warmblood horses, few died or were
Comparison of the two warmblood horse popula- culled due to diseases of the circulatory system and
tions included in this study revealed that the pre- tumours, and none among the coldbloods. A differ-
dominant causes of culling in both populations were ence between the two groups of warmblood horses
diseases of the musculoskeletal system, in which the was noted regarding accidents. In the RHQT data,
proportions of deaths, 56 and 57, were very accidents 9 formed the second largest cause of
similar. In both studies, diseases of the joints and death, whereas in the CHF data only 2 of the
skeleton were a major cause, representing 73–82 horses died as a result of accidents. These differ-
of all causes of culling in the musculoskeletal disease ences may reflect variations in management stan-
group. According to studies based on insurance data, dards among the RHQT horse owners.
61 Clausen et al., 1990, 57 Heisele, 1995 and According to the results of the present study,
47–56 Hommerich, 1995 of sports horses were coldblood horses differed considerably from the
culled because of diseases of the musculoskeletal warmbloods and were less often affected by lame-
system. Baker and Ellis 1981 investigated causes ness 13, than by temperamental disorders 23.
288 L
. Wallin et al. Livestock Production Science 63 2000 275 –289
Diseases of the nervous system were also quite lished diagnosis of identified horses with their pedi-
common 16 among horses in the study by Baker grees, which is necessary for reliable genetic analysis
and Ellis 1981. The proportions of coldblood and and selection decisions.
warmblood horses that died from diseases of the When we know more about the diseases that are
digestive system were almost identical about 6, the cause of most deaths in horses, efforts must be
whereas few 2 coldblood horses were affected by made to apply this knowledge to alleviate and
diseases of the respiratory system. A difference hopefully diminish the problems. It is important to
between coldblood and warmblood horses was also make improvements in the management and training
found regarding
hoof diseases,
where 8
of of horses and also to make genetic selection more
coldbloods were culled compared with 3 of the effective. However, for most diseases the mode of
warmbloods. inheritance for those with an anticipated genetic
Apparently, there are differences between reasons background needs to be more thoroughly investi-
for culling and death for different horse breeds and gated, as well as other factors that influence the
horse categories. This was evident both in this study development of the diseases.
and in the literature Baker and Ellis, 1981; Clausen et al., 1990; Heisele, 1995; Hommerich, 1995.
Differences were found between riding sports horses