Estimation of the genetic diversity in the Mini-Lewe breeding population and influence of inbreeding on litter traits

The Mini-Lewe was bred as an animal model for experimental research in the former Democratic Republic of Germany. The remaining stock, including 5 boars and 10 sows, was transferred from the Humboldt-University Berlin to the experimental and teaching farm Ruthe (LFG Ruthe) of the University of Veterinary Medicine Hannover Foundation in 2005. Since then, the Mini-Lewe was bred at the LFG Ruthe. The present study has the objective to perform a population genetic analysis of this Mini-Lewe breeding population based on pedigree data to evaluate genetic diversity and degree of inbreeding as well as inbreeding depression on litter size traits. The results of the comparative analysis of the original population in 2005 with the current population of 2018 showed a loss of genetic diversity. In the population of 2018, the mean inbreeding coefficient was 11.7%, the mean increase in inbreeding was 1.2%, the effective population size included 13 individuals and the number of effective founder genomes was 2.4. Significant negative effects due to an increase of inbreeding coefficients and individual rates of inbreeding of the dams were observed for the total number of piglets born, piglets born alive and piglets weaned per litter. A similar increase in inbreeding coefficients and individual rates of inbreeding of the sire also had significant negative effects on the number of piglets born alive per litter. Maximal expectation for the effect of an increase in inbreeding showed a loss of up to one piglet weaned per litter. In conclusion, as only five piglets are weaned per litter on average, measures to preserve the Mini-Lewe breeding population at the LFG Ruthe should be implemented. Therefore, long generation intervals were considered as essential and mating management minimized relationship coefficients using all available pedigree information. As a further measure, sperm conservation of breeding boars is being planned.