Abstract
Simple SummaryThe main aim of modern breeding programs in dairy cows is to improve productivity, functional and health traits. The use of only a few top sires leads to more efficient milk production, but also it could lead to a decline in the gene pool, smaller effective population size and an increase of inbreeding. Deleterious effects of inbreeding in dairy cattle may reduce the benefits of the genetic gains. Due to this fact, it is important to monitor the genetic diversity in dairy cattle breeds. In this study, pedigree data were used to show the losses of genetic variability and its association with the heavy use of imported US Brown Swiss bulls and semen in the German Brown population. Strategies to decrease rate of inbreeding through sires with less relationships to the most important ancestors should be considered in future breeding strategies.Increase of inbreeding and loss of genetic diversity have large impact on farm animal genetic resources. Therefore, the aims of the present study were to analyse measures of genetic diversity as well as recent and ancestral inbreeding using pedigree data of the German Brown population, and to identify causes for loss of genetic diversity. The reference population included 922,333 German Brown animals born from 1990 to 2014. Pedigree depth and completeness reached an average number of complete equivalent generations of 6.24. Estimated effective population size for the German Brown reference population was about 112 with a declining trend from 141 to 95 for the birth years. Individual inbreeding coefficients increased from 0.013 to 0.036. Effective number of founders, ancestors and founder genomes of 63.6, 36.23 and 20.34 indicated unequal contributions to the reference population. Thirteen ancestors explained 50% of the genetic diversity. Higher breed proportions of US Brown Swiss were associated with higher levels of individual inbreeding. Ancestral inbreeding coefficients, which are indicative for exposure of ancestors to identical-by-descent alleles, increased with birth years but recent individual inbreeding was higher than ancestral inbreeding. Given the increase of inbreeding and decline of effective population size, measures to decrease rate of inbreeding and increase effective population size through employment of a larger number of sires are advisable.
Highlights
Due to the high breed proportions of US Brown Swiss in the German Brown population, we evaluated the influence of increasing breed proportions of US Brown Swiss on the degree of inbreeding
The amount of genetic diversity lost in the reference population since the founder generation due to bottlenecks and genetic drift (1 − GD) was 0.025 and due to genetic drift 0.017 (GD* − GD)
Results of this study indicate a loss of genetic diversity in the German Brown population due to drift and unequal founder contributions
Summary
German Brown has its roots in grey-brown cattle populations including the Allgäuer and Württemberger Braunvieh, Graubraunes Tiroler. Brown Swiss bulls into the German Brown population started in 1966 and became part of the breeding strategy due to the enormous superiority in production efficiency of US. Brown Swiss compared to German Brown cattle at the time [4]. The breed proportion of US Brown Swiss increased in today’s German Brown cows to about 70% [5]. Focusing on a small number of superior bulls leads unavoidably to an increase of inbred animals and to a decline of genetic variability in the population which can negatively influence the performance and reduce fitness traits in dairy cattle [6,7,8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
