Analysis of systematic and genetic effects on weight and body measurements and their relationships with canine hip dysplasia in German shepherd dogs

The objective of the present thesis was to analyze systematic and genetic effects on weight and body measures and their relationships with canine hip dysplasia (CHD) in the German population of German shepherd dogs (GSD). Furthermore currently practiced selection strategies with respect to CHD were evaluated. Finally the diversity within litters with regard to body measures, which are part of the breeding standard, were analyzed. Because dog breeding is always a multitrait selection it was important to know whether there are relevant relationships between the analyzed conformation and health traits, such as CHD, which could be used to improve future breeding success. Breeding standards for dogs usually define the lower and upper limits of body measures that a dog needs to fulfil to get the permission for breeding. Available data included conformation information from 36,028 breeding dogs born between 1992 and 2003 with measurements of withers height (WH), chest height, chest circumference and body weight (BW). Analysis of variance was performed for the systematic effects sex, birth year, month of birth, region, age at licensing, litter size and inbreeding coefficient. Birth year, month of birth, region and age of breeding approval were in most cases significant for the traits analyzed. Inbreeding coefficient was significant as a nonlinear covariate for withers height and chest circumference. The pedigree file used for the genetic analysis consisted of 574,356 registered animals born between 1985 and 2006. The genetic parameters were estimated in linear animal models using the residual maximum likelihood (REML). Uni- and bivariate analyses were performed for both sexes together and separately for males and females. The male dogs had a mean withers height of 64.4 cm and a mean body weight of 36.5 kg. Female dogs had a mean withers height of 59.2 cm and a mean weight of 29.0 kg. Heritability estimates for both sexes together were 0.41 ± 0.01 for withers height and 0.27 ± 0.01 for body weight. For the other traits studied, heritability estimates were lower with values of 0.20 ± 0.01 for chest height and 0.13 ± 0.01 for chest circumference. In the separate analyses for male and female dogs, heritability estimates were higher for females. Additive genetic correlations in the order from 0.91 to 0.98 between corresponding traits in males and females indicated an equal genetic basis of body measures in both sexes. It can therefore be concluded that selection for conformation traits will equally affect both sexes and will not increase sexual dimorphism in dogs. Thus future analyses of body measures could be performed for both sexes together. For the analyses of relationships between WH, Body Mass Index (BMI), i.e. the quotient of BW and squared WH, and CHD, body measures of 31,398 dogs and CHD scores of 105,756 GSD born between 1992 and 2003 were considered. The pedigree contained 141,100 animals, including ancestors for up to four generations and 6,175 base animals. Genetic parameters were estimated bivariately in linear animal models using Gibbs sampling with the program MTGSAM. Distribution of CHD scores in progeny by WH and BMI of their parents indicated that there was no obvious phenotypic correlation between CHD and body measures. Estimated additive genetic heritabilities of the animal were 0.18 ± 0.01 for CHD, 0.49 ± 0.04 for WH and 0.17± 0.02 for BMI. Given the low phenotypic and genetic correlations ranging between -0.07 and 0.07 between CHD on the one hand and WH and BMI on the other hand, it can be concluded that dog breeding with focus on CHD will have a very slight influence on body measures and vice versa. WH and BMI may not be very useful as accessory traits for selection against CHD. In the GSD, selection against CHD is practiced for decades, but mass selection and pedigree breeding value (PBV) based selection for CHD have not yet led to satisfactory improvement of the CHD status in the German population of GSD (Janutta et al. 2008). To find reasons for the slow breeding progress the ability of PBV to predict offspring phenotypes compared with selective breeding based on the CHD phenotype of parents was investigated. Official scores for CHD of 184,489 GSD from birth years 1985 to 2007 were included in the genetic analyses. Pedigree information on up to eight generations was considered, resulting in a relationship matrix of in total 200,853 dogs. Breeding values were predicted under the assumption of a heritability of CHD of 0.20 by Best Linear Unbiased Prediction (BLUP). Proportions of explained phenotypic variance lower than 1% for selection based on parent phenotypes only, and 2 to 3% for selection based on PBV explain the little success in CHD elimination. Therefore, selection using PBV maybe preferable over mass selection but selection response for CHD is limited. In the GSD current means of WH and BW are close to the upper limits defined in their standard. Therefore, the expected selection response for conformation and conformational homogeneity was investigated. Body measurements were available for 36,028 dogs born between 1992 and 2003, 14,416 male and 21,612 female GSD from 26,155 litters. WH and BMI, i.e. the quotient of BW and squared WH, were considered as traits to directly select for certain size and stature. Within litter variance of WH (vWH) and BMI (vBMI) were defined as traits to select for conformation homogeneity of litters with at least two dogs with conformation data. To monitor possible side effects of conformation selection for CHD, CHD scores for all dogs were used. Genetic parameters were estimated multivariately in linear animal models using Gibbs sampling. Heritabilities ranged between 0.19 and 0.34 for all traits with additive genetic correlation of -0.11 between WH and vWH and 0.11 between BMI and vBMI. Breeding values (BV) for WH and BMI were negatively correlated with -0.20 in sires and -0.17 in dams. Expected selection response was studied using relative breeding values (RBV) of parents, assuming exclusion of sires and/or dams with RBV larger than 120, and comparing means of WH, BMI and CHD score between offspring of all and selected parents. Concurrent selection for small WH and vWH was found to most efficiently reduce mean WH in males and females while having little impact on CHD distributions. Multiple trait selection for WH, vWH, BMI and vBMI was hindered by the negative genetic correlations between the traits and tended to interfere with improvement of CHD status. Use of RBV for WH and vWH for conformation selection is therefore recommended to maximize breeding success with regard to conformation and conformational homogeneity in the GSD.