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Doctoral thesis, 2017

Genetic evaluation of susceptibility to- and recoverability from mastitis in dairy cows

Welderufael, Berihu

Abstract

Mastitis has been the focus of many dairy cattle research projects over the last decades. However, in the genetic evaluation of udder health, only susceptibility to mastitis has been considered, leaving aside the other aspect of the disease - the recoverability. The aim of this thesis was to improve the genetic evaluation of udder health by introducing a new approach and models that can make use of the information contained in both directions: susceptibility to- and recoverability from mastitis. In paper I, extensive simulation analyses were performed to develop a bivariate model for joint genetic evaluations of susceptibility to- and recoverability from mastitis. In paper II, the bivariate model with an added time function as well as several systematic effects was applied to real data to estimate genetic parameters in Danish Holstein cows. In paper III, genome-wide association studies were conducted to identify associated single-nucleotide polymorphisms and thereof candidate genes. In paper IV, a dynamic health classification, which takes severity of possible infection into account was introduced to further improve the genetic evaluation of mastitis. Findings in paper I demonstrated that both traits can be modelled jointly and genetic parameters could be correctly reproduced. In paper II, we detected presence of genetic variation that resulted to heritability (ranging from 0.06 to 0.08) of similar size for both traits. The between trait genetic correlation was -0.83. Despite the strong negative genetic correlation, association signals in paper III did not overlap, suggesting that the traits are at least partially regulated by different genes. Complexity of the traits was manifested with the absence of strong association signals. In paper IV, considerable genetic variation was detected for cows’ presence in health classes defined for longer periods, whereas the variations in health classes defined for short-term and sudden changes (e.g., acute) were mostly attributed to environmental factors. Although susceptibility to- and recoverability from mastitis are strongly negatively correlated, recoverability which is as heritable as susceptibility could be considered a new trait for selection. Evaluating and modelling the ability of animals to overcome infection could be of specific benefit in situations of high disease incidence.

Keywords

bivariate model, dairy cow, genetic evaluation, mastitis, recoverability, susceptibility

Published in

Acta Universitatis Agriculturae Sueciae
2017, number: 2017:71
ISBN: 978-91-7760-032-9, eISBN: 978-91-7760-033-6
Publisher: Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences

Authors' information

Welderufael, Berihu
Swedish University of Agricultural Sciences, Department of Animal Breeding and Genetics
Welderufael, Berihu
Aarhus University

UKÄ Subject classification

Animal and Dairy Science

URI (permanent link to this page)

https://res.slu.se/id/publ/104143