Materials competition results as well. It was not unusual that

276 L . Wallin et al. Livestock Production Science 63 2000 275 –289 compensation had been granted. These estimates were never found 30. Among those traced, the should not be confused with the average expected response frequency to the questionnaires was 78. life span of all horses in the population, because of Ninety-nine horses had been exported and were not lack of information on horses still alive and on included in the study due to lack of information horses not compensated for at death. Such estimates about their health status. The number of horses would therefore most likely underestimate length of finally included in the study was 1847, 503 of whom life Ohlsson, 1990. were dead. The distribution between mares and Survival analysis, a statistical technique that can males was fairly even 864 983. Of the males 74 use information on horses still alive, so-called cen- were stallions at the time of the test. Information sored data, is a more appropriate way to estimate the about the horses was available until 1990. Horse length of life of horses. More accurate estimates of owners were asked if particular horses were alive or length of life would bring better information to the dead and, if dead, to state the cause and year of debate about equine longevity. death. When analysing the questionnaires, no distinc- Reports summarising causes of death in sports tion was made between horses that died and those horses are rare. Many studies mention a specific that were put down, because death was considered to disease affecting horses and are often based on a be due to the causes mentioned in the questionnaires. relatively selected group of horses Baker and Ellis, The date of birth ranged from 1968 to 1982 Fig. 1981. Available statistics are based mostly on 1. The horses were usually 4 years old when they insurance data or veterinary clinical studies. Accord- participated in the test, the oldest horses in the ing to insurance statistics, diseases of the musculo- material could have reached an age of 22, whereas skeletal system are the predominant cause of death of horses born in 1982 could not have been more than 8 sports horses Clausen et al., 1990; AGRIA, 1995; years old. When the test started in 1973, participation Heisele, 1995. Among ‘companion’ horses kept as a was limited because all horses were judged at only hobby, diseases of the digestive system are the most one location in Sweden. Later, more places became frequent cause of death Baker and Ellis, 1981. available and interest in participating increased. Other than insurance statistics, recent reports on The horses included in the study had been used for length of life and the most important causes of death different purposes — many of them for more than in horse populations are scarce. This emphasizes the one purpose Table 1. Most horses 85 had been need to find unselected materials in order to establish competing in different disciplines. It was quite appropriate benchmarks. The aims of this inves- common that horses competing at a novice level had tigation, therefore, were to estimate median length of results in several disciplines, whereas horses compet- life and to analyse and compare causes of death in ing at an advanced level had results only in one of different Swedish horse populations representative of the disciplines. An earlier study Ohlsson and Philip- their breeds and normal use. sson, 1992 showed that horses with high scores in the test had competed more successfully than the others at advanced levels. Many brood-mares had

2. Materials competition results as well. It was not unusual that

former competition horses were used as leisure 2.1. Swedish Riding Horse Quality Test data horses after their competition career was over. Few horses 4 had been used in riding schools. RHQT Data were obtained via questionnaires sent to data were analysed by sex because mares had a value owners of Swedish warmblood horses that as 4-year- as breeding animals besides competition, which olds had participated in the Riding Horse Quality geldings did not. Tests RHQT between 1973 and 1986. For a description of the test, see Ohlsson and Philipsson 2.2. Swedish Cavalry Horse Foundation data 1992. Horses participating in the tests were found to be desirable for competition riders and many of Data on 344 Swedish warmblood horses, 208 of them had changed owner at least once. However, this whom were dead, and 204 coldblood horses, 97 of made it difficult to trace the horses and some of them whom were dead, were made available by the L . Wallin et al. Livestock Production Science 63 2000 275 –289 277 Fig. 1. Questionnaire response: number of horses in Riding Horse Quality Test, distributed by birth year and sex. Table 1 compared with 5 of the coldbloods. Information Use of horses that participated in the Riding Horse Quality Tests about the horses was available up to 1989. Area of activity Number Percentage of horses 2.3. Swedish Warmblood brood-mare data n 51847 Competition 1563 85 A third population was included in the study, stud Show jumping 1201 65 book mares of the Swedish Warmblood breed, in Dressage 892 48 order to compare two groups of females of the same Eventing 187 10 breed. All brood-mares born between 1965 and 1967 Driving 23 1 a Breeding 521 28 and registered with a foal for the first time in the Leisure riding 497 27 1971 stud book were included. The mares were then Riding school 78 4 4–6 years old. It was important to find mares as Miscellaneous 54 3 young as possible when they entered the stud book in a Twelve of 74 stallions were used for breeding. order to identify those that could have died early at an age of just 4 years or over, thereby allowing a reasonable estimate of length of life. The last stud Swedish Cavalry Horse Foundation CHF. Among book included information up to 1991. The study the warmblood horses, the cavalry had preferred included 481 brood-mares, 266 of whom were dead. buying geldings. Thus, their material included only There was no information on the causes of culling or 38 mares, whereas the distribution between sexes death in this material. among the coldblood horses was more even: 115 RHQT horses represented in general sport horses geldings and 89 mares. Both groups of horses were while the last two populations represented riding born between 1970 and 1975. The CHF bought the school horses and brood-mares within the same horses as 3-year-olds. breed. Thus, possible differences in longevity and or The cavalry in Sweden needed horses for various causes of death depending on population area of purposes, but because many cavalry regiments had activity were covered in the study. been disbanded and the need for the horses was concentrated to short periods during the year, horses were loaned out after 1 year of training. Riding

3. Methods