[Genetic and epidemiological investigation of a birth cohort of boxers]. / Genetisch-epidemiologisch onderzoek in een geboortecohort boxers.

The aim of this project, which ran from 1 January 1994 to 1 January 1999 (and which will be continued up to 2004), was to study mortality, disease incidence, and risk factors in a birth cohort of purebred boxer dogs born between January 1994 and February 1995 in the Netherlands (n = 2629). The ancestry of the boxer dogs in the cohort was considered a major risk factor. Special attention was given to genetic disorders, because a system for genetic counselling was being planned; however, non-genetic risk factors were also studied. Participation by breeders and owners of boxer dogs was very high. Pup mortality was 22% and was mainly caused by individual pup factors. Between 2 months and 4 years of age, 123 (7.5%) dogs died; the survival rate was 92.5%. The main causes of death were epilepsy (n = 23), heart disease (n = 22), and traffic injury (n = 13). Over the same age range, on average a boxer dog suffered about 4.25 times from a non-serious disease, mainly of the gastro-intestinal tract, upper respiratory tract, or locomotion system, but 20% had a serious, chronic disease. A relatively high heritability estimate (h2) was found for four diseases: cheilo-palatoschisis (h2 = 0.27), cryptorchism (h2 = 0.24), lesions of cruciate ligaments and menisci (h2 = 0.28), epilepsy (h2 = 0.36). Selection by means of genetic counselling, according to a programme developed on the basis of the results of this study, can reduce the frequency of these genetic diseases in purebred populations of boxer dogs. This genetic counselling programme will also be effective in other breeds of dog because it is based on linking specific pedigree and health information with a generally applicable method of estimating breeding values.

Heritability estimations for diseases, coat color, body weight, and height in a birth cohort of Boxers.

OBJECTIVE: To obtain heritability estimates for diseases and characteristics in Boxers. ANIMALS: Birth cohort of 2,929 purebred Boxers from 414 litters. PROCEDURE: Heritability estimates were determined for cheiloschisis-palatoschisis, cryptorchidism, epilepsy, stifle disorders, cardiac disorders, coat color, birth weight, and adult weight, and height. Binary traits were analyzed by use of a mixed-effects probit model. Some traits also were analyzed by use of a model that postulated monogenic inheritance. Full pedigree analyses were performed. Variation in incidences of disease among clusters of related dogs was evaluated. RESULTS: Heritability estimates were virtually zero for cardiac disorders, medium (0.17 to 0.36) for most other traits, and high (> 0.55) for coat color, birth weight, and adult height. Litter effects and risk factors affected cheiloschisis-palatoschisis, heart murmur, coat color, broadly defined epilepsy, and adult weight. Litter effects may be attributable to common environmental effects for littermates but also may be attributable to dominance variation caused by a recessive gene. Heritability estimates increased when stricter definitions for epilepsy and stifle disorders were used. The monogenic model did not reveal higher heritability estimates for 6 traits analyzed. Incidences for white coat differed significantly for 10 familial clusters, confirming high heritability and effects of familial lineage. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that genetic improvement of most traits should be feasible, except for cardiac disorders. However, because most traits are influenced by environmental effects as well as genetic effects, genetic counseling based on polygenic inheritance and use of familial information rather than strict exclusion of parents is preferred.

Population parameters to compare dog breeds: differences between five Dutch purebred populations.

Differences in five purebred dog populations born in 1994 in the Netherlands were evaluated using different parameters. Numerically, the Golden Retriever was the largest breed (840 litters of 234 sires) and the Kooiker Dog (101 litters of 41 sires) the smallest. The litter per sire ratio was largest in the Bernese Mountain Dog (4.59) and lowest in the Kooiker Dog (2.46). The mean relatedness and the actual mean level of inbreeding in the studied generations were 0.102 and 0.056 respectively for the Bernese Mountain Dog, 0.041 and 0.046 for the Bouvier des Flandres, 0.087 and 0.061 for the Boxer, 0.020 and 0.018 for the Golden Retriever, and 0.146 and 0.070 for the Kooiker Dog. Quantification and visualization of population parameters for purebred dogs will facilitate the comparison of breeds and the comparison of breeds in different periods or countries. It appears unlikely that the increase in inbreeding is a major determinant of the possible increase in the frequency of genetic diseases.

Evaluation of genetic, common-litter, and within-litter effects on preweaning mortality in a birth cohort of puppies.

OBJECTIVE: To determine relative impact of genetic, common-litter, and within-litter factors on puppy mortality. ANIMALS: 2,622 Boxer puppies of 413 litters born during a 14-month period. PROCEDURE: For each puppy, pedigree was determined, and litter in which it was born was registered. Overall mortality and mortality per specific cause of death were analyzed by use of a model that included an additive genetic effect, common-litter effect, within-litter effect, and regression of mortality on inbreeding coefficient. Relative importance of the effects was determined from estimates of the variance in mortality explained by each factor. RESULTS: 22% of the puppies died before reaching 7 weeks old. Stillbirth was the most frequent cause of death, followed by infection. Most observed differences were attributable to within-litter factors, which explained 67% of the variance in death attributable to infection and < or = 96% of the variance in death attributable to asphyxia. Common-litter factors were more important than additive genetic factors. Variance attributed to common-litter factors ranged from 2% for cheiloschisis, palatoschisis, or cheilopalatoschisis to 30% for death attributable to infection, and variance attributed to additive genetic factors ranged from 0% for asphyxia to 14% for euthanatized because of white color. Inbreeding coefficient had a significant effect on death attributable to infection, which increased 0.26% for each percentage increase of inbreeding. CONCLUSIONS AND CLINICAL RELEVANCE: Additive genetic factors have less impact on preweaning mortality than common-litter factors, which in turn have less impact than within-litter factors. Mortality attributable to infection increases significantly with increases in inbreeding.

Investigation of mortality and pathological changes in a 14-month birth cohort of boxer puppies.

This paper presents puppy mortality and postmortem findings for a birth cohort of boxer puppies born in the Netherlands between January 1994 and March 1995. In all, 457 litters were registered, of which 414 (90.6 per cent) were involved in the study. The 414 litters contained 2629 puppies, a mean litter size of 6.4 puppies. Of the 2629 puppies 571 (21.7 per cent) died or were euthanased before they were weaned at 50 days of age; there were 147 (25.7 per cent) stillbirths; 102 (17.9 per cent) were euthanased because they were white; 269 (47.1 per cent) of the puppies died during the first 21 days of life and 53 (9.3 per cent) puppies died between days 22 and 50. The cause of death or the reason for euthanasia was assessed by either the breeder or the veterinarian in 176 of these 269 puppies but was not determined in the other 93 puppies. Three hundred and two puppies were examined postmortem; the most important cause of death or reasons for euthanasia were inflammatory disorders (102; 33.8 per cent), non-inflammatory disorders such as asphyxia and malnutrition (66; 21.9 per cent), euthanasia because they were white (51; 16.9 per cent), and congenital abnormalities (45; 14.9 per cent). No cause of death or reason for euthanasia could be found for 38 puppies (12.6 percent)