The aim of this thesis was to examine the relationship between inbreeding and performance in the Hanoverian Sport Horse.
A total of 84,724 hanoverian horses born between the years 1990 and 2009 were used for the study, of which 78,907 had their own performance records. Pedigree records were traced back as far as possible, with a maximum of 37 generations used. There was 100% completeness of pedigree up to the grandparent generation for all horses. The majority of horses (80%) had completeness of pedigree past the sixth generation.
Inbreeding were calculated using two methods; the Meuwissen method and the van Raden Method. Both methods gave identical results (100% fit). As aquantitative measure of performance, the Integrated Estimated Breeding Value (iEBV), using both breed and competition results was used. The Evaluation was carried out using the BLUP (Best Linear Unbiased Prediction) Multitrait Repeatability Animal Model. Two different GLM were run with the inbreeding coefficient (IBC) modelled as either a continuous variable or as a fixed class of five differing levels of inbreeding (IBC=0.00; 0<IBC≤0.01: 0.01<IBC≤0.02; 0.02<IBC≤0.05; 0.05<IBC). Age and Sex were included as fixed effects within the model.
All subgroups in both dressage and jumping data, with either fixed effect or linear covariate for the IBC, generated a similar result. Due to the large sample size there was a significant (p<0.001) relationship between inbreeding (IBC) and performance (iEBV). In dressage horses there was a significant positive relationship in all categories while in jumping horses there was a significant negative relationship in all catagories. However, the effect of inbreeding on iEBV explained only ±1% of the variance in the models. The models were simultaneously adjusted for the bias of the confounding factor of sex which also accounted for ±1% of the variance. The majority of variance in iEBV is due to the year cohort effect which accounts for ± 95%. The low level of inbreeding (±1.5%) and lack of biological effect on iEBV indicate that inbreeding is not a problem in the Hannoverian horse.