Browsing by Author "Åhlgren, Johanna"

Hovawart is an old German working dog breed. Few hundred dogs are registered annually in Finland. Hovawarts can be seen in working trials as well as a family pet. In Hovawart breeding program (JTO) hypothyroidism is mentioned as a one of the most common hereditary diseases and is usually caused by lymphocytic thyroiditis. Lymphocytic thyroiditis is an autoimmune disease which destroys the thyroid gland. Hypothyroidism is treated medically by substituting natural hormone production with medical hormones. The aim of this study was to estimate the heritability of the hypothyroidism in Finnish Hovawart population. Research material was provided by Finnish Kennel Club and Finnish Hovawart Club. Dogs born between 1990 and 2010 were included in the study. The influence of gendre, birth year and month, size of the birth litter, breeders living area, colour and inbreeding were studied. Data was delimited in two different ways. Data 1 consisted 4953 dogs, where 107 were hypothyroid and 4846 were assumed to be healthy. In data 2, hypothyroid dogs were the same as in data 1 but only dogs used for breeding were considered as healthy (739 dogs). The χ2 test was used to evaluate the influence of individual factors. The influence of fixed effects and covariate were tested with a generalized linear model. Fixed effects were chosen by using the backward method and the applicable model was chosen by using e.g. Akaike’s information criterion, AIC. The animal model and the REML method was used in variance component analyses. Since hypothyroidism is a binary factor logit and probit models were used. For comparison, heritability was also estimated with a linear model. In data 1 colour and birth litter size were significant. In data 2 colour, birth litter size and gender were significant. Estimated heritability by logit model was 0.65 in data1 and 0.54 in data 2. When transformed to the underlying liability scale the corresponding values were 0.36 and 0.26, respectively. Heritabilities by probit model were 0.24 and 0.23 and by linear model 0.21 and 0.44 for data 1 and 2, respectively. Heritability of hypothyroidism is moderate and can be considered even as high, hence the prevalence of hypothyroidism can be decreased by breeding. However, it is not possible to exclude all hypothyroid dogs and their close relatives from breeding. Hypothyroidism can be diagnosed later when the dog has already been used for breeding. To decrease the prevalence of hypothyroidism there is a need for an appropriate tool to support breeders’ choices. Efficiency requires openness within breed and collecting and offering the data to public use.