Selection for conformation and conformational homogeneity of litters in the German shepherd dog.

Breeding standards of most dog breeds specify tolerable ranges of certain conformation traits. In the German shepherd dog (GSD), current means for withers height (WH) and BW are close to the upper breed limits. Therefore, strategies to avoid a further increase in size and to maximize the proportion of dogs fitting the breeding standard with respect to WH and BW should be compared. Body measurements were available for 14,416 male and 21,612 female GSD from 26,155 litters. Withers height and body mass index (BMI; i.e., BW/WH(2)) were considered direct selection traits. Using information on 17,154 GSD from litters with at least 2 dogs with conformation data, we defined within-litter variances of WH (vWH) and BMI (vBMI) as traits to select for the conformational homogeneity of litters. Officially recorded scores for canine hip dysplasia (CHD) of all dogs were used to monitor possible side effects of conformation selection on CHD. Genetic parameters were estimated multivariately in linear animal models by using Gibbs sampling. Heritabilities ranged between 0.19 and 0.34 for all traits, and additive genetic correlations between WH and vWH were -0.11 and those between BMI and vBMI were 0.11. The expected selection response was studied using the relative breeding values (RBV) of parents, assuming exclusion of sires, dams, or both with RBV larger than 120 and comparing means of WH, BMI, and CHD scores between offspring of all and selected parents. Concurrent selection for small WH and vWH was found to reduce the mean WH in males and females most efficiently while having little effect on CHD distributions. Multiple-trait selection for WH, vWH, BMI, and vBMI was hindered by the negative genetic correlations between the traits, and it tended to interfere with improvement of CHD status. Use of the 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.