Download Less mastitis through targeted selective breeding Why a reduction of

Less mastitis through targeted selective breeding
Mammary
Function
In this project genes and genetic pathways involved in the immune
response of dairy cows were identified. These findings have enhanced our
understanding of the functional role of these genes and genetic pathways
in bovine mastitis. Our discoveries will enable us to better understand the
immunological consequences of using genome-wide selection.
‘Mastitis is an
inflammatory reaction
in the mammary gland
due to invasion and
colonisation by diverse
pathogens’
Definition
EU
 Number of dairy cattle:
23,7 million
 Estimated number of
dairy cattle affected by
mastitis: 6,9 million
(30 % of the population)
 Annual estimated cost of
mastitis per animal:
€150 - €300
 Annual total costs of
mastitis: €2 billion
Why a reduction of mastitis?
Mastitis is of major concern. It
causes suffering to many cows. With
an annual cost of €2 billion in Europe
alone, it is the most costly disease
in dairy cattle. It is also the most
frequently occurring disease and its
incidence has not declined despite
improved methods of prevention
and treatment as well as breeding
for genetic resistance against
mastitis. Mastitis is also the leading
cause of antibiotic use in dairy
production. Increasing resistance to
mastitis will therefore decrease use
of medicines, and simultaneously
improve animal welfare, food safety,
product quality and economic
returns.
It is difficult to improve resistance to
mastitis by traditional means, as the
genetic resistance to clinical mastitis
is negatively correlated to milk yield
and other economically important
production traits. However, progress
using selective breeding could be
improved substantially by the use
of new genomic tools. Using new
genomics technologies assisted this
project in identifying important
genes and genetic pathways involved
in the immune response to mastitis.
Research for healthier udders
Genome-wide association analysis was used to identify genomic
regions affecting the resistance to mastitis. Genome-wide
expression profiling was used to identify genes involved in the
local (mammary gland) and the systemic (e.g. liver) acute phase
response in dairy cows during infection.
Genome-wide associations
Linkage and linkage disequilibrium
analyses as well as genome-wide
association analysis were used to
identify several quantitative trait
loci (QTL) affecting the resistance to
clinical and subclinical mastitis. The
sizes of these genomic regions were
typically in the range of several million
DNA base pairs. Each region contained
a plethora of genes of which
some play a critical role in mastitis
resistance either as single genes or in
combination. They can, for example,
also interact as partners in protein
complexes. Further investigations
showed that these QTL affected the
levels of genetic resistance specifically
against the most common mastitis
pathogens, including S. aureus and
E. coli.
Genome-wide expression
To complement these studies and to
gain further insight into the genetic
background for mastitis-related traits,
genome-wide expression analyses
of udder and liver tissues during
infection were applied. These analyses
further increased our understanding
of the disease pathogenesis of
mastitis. Global changes in expression
levels of genes were identified and
revealed genetic pathways that are
associated with bovine mastitis.
Candidate genes
The key challenge for the future is
to prioritise and select the most
probable candidate gene(s) for indepth molecular analysis. These genes
will be selected from a long list of
differentially expressed genes caused
by mastitis infection, or from the
hundreds of genes located in mastitisassociated gene regions (QTL). To
do this, this project developed a
bioinformatic approach for ranking
genes associated with quantitative
traits and diseases in livestock
species. The approach was applied
to rank all known genes present in
the cattle genome for their potential
roles in bovine mastitis, and also to
prioritise candidate genes located
in a QTL affecting the susceptibility
to mastitis. The top ranked genes
were highly enriched for pathways
underlying inflammation and immune
responses, which supports the validity
of our approach to identify genes
that are relevant to animal health and
disease.
Partners
Aarhus University
The Roslin Institute
ARO
MTT
Denmark
UK
Israel
Finland
Contact details
[email protected]
This research project has been co-financed by the European Commission,
within the 6th Framework Programme, contract No. FOOD-CT-2006-016250.
The text represents the authors’ views and does not necessarily represent a
position of the Commission who will not be liable for the use made of such
information.
Project Office SABRE
Coordinator Chris Warkup
Biosciences KTN, The Roslin Institute,
Easter Bush, EH25 9RG, UK
www.innovateuk.org/biosciencesktn
www.sabre-eu.eu