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Success story: Genetic tools to improve mastitis resistance in dairy cattle

Milk production is the most important agricultural activity in the EU, with over 18 % of the total value of agricultural production. Mastitis is the most common disease in dairy cows and its incidence has not declined with improved methods of prevention and treatment. This disease is a major concern as it causes cows to suffer; it is the most costly disease to dairy farmers and leads to the highest antibiotic use in livestock production. The MASTITIS RESISTANCE EU-funded project developed alternative genetic approaches to mastitis reduction.

By identifying major loci affecting resistance to mastitis and the application of genotype based marker assisted selection to breed for improved mastitis resistance, the MASTITIS RESISTANCE project, funded under the 5 th Framework Programme, has provided tools that allow the agricultural sector to address the concerns of consumers. Reduction in mastitis incidence through genetics will improve the health of cattle and the safety and quality of their products, reduce the need for antibiotics and reduce the chemical pollution of the environment. The results support the use of diverse breeds, and act against concentration on a single dairy breed. In addition to the benefits to the primary producer, improved health will allow the development of larger livestock markets for European dairy cattle, offering opportunities for job creation in rural areas.

The challenge

Major loci that influence important traits in livestock (quantitative trait loci, QTL) can be detected by whole genome scans. However, the resolution achieved by traditional interval mapping is poor with the likely location for the QTL often spread across tens of centiMorgans. This genetic distance represents a considerable length of DNA that may contain hundreds of genes. Identifying the causative gene mutation would allow selection to be carried out in new populations for which genotypic and phenotypic information is not yet available. Indeed, the major challenge in mapping complex traits lies not in detecting QTLs but in pinpointing the underlying genes.

The overall objective of the MASTITIS RESISTANCE project was to develop tools to confirm, fine-map and identify genetic loci harbouring genes underlying variation in mastitis resistance in dairy cattle and to use these tools for fine mapping in a large Nordic resource population with extensive records of mastitis incidence. Such tools are needed to obtain the full benefits of the project in all the dairy breeds within the EU whilst maintaining their diversity.

Fine mapping of gene loci

The partners of the MASTITIS RESISTANCE project successfully developed a software and genomic tools that will be freely available to the scientific community. The statistical methodology developed provides the possibility to map loci as precisely as possible using multiple trait information and multiple loci, taking into account the problems encountered in the real-life datasets, such as null alleles. This combination of mapping technology is at the cutting edge. In addition to the advances in fine mapping methodology, the consortium also produced a user-friendly statistical tool, called "InSure", for marker assisted introgression.

Genetic resistance to mastitis

Some marker haplotypes identified on chromosome 9 of the Nordic dairy cattle were shown to confer benefits in resistance to clinical mastitis. The finding is mainly based on veterinary treatment data collected by the Nordic breeding companies/dairy associations and used in genetic evaluation for tens of years. Therefore, marker haplotypes associated with mastitis resistance within each breed are confidential information, which will not be published before intellectual property right protection. A patent application "Mastitis resistance" was filed on February 2006 in Denmark based on this result. The breeding companies are very interested in the implementation of marker technology in their existing and future breeding schemes, both in progeny testing systems and in nucleus breeding systems. The knowledge can be used for marker-assisted selection in the Nordic red breeds. Within breeds the dissemination of the benefits would be through selection of favourable alleles using marker-assisted selection tools already developed. The transfer of alleles between breeds requires additional tools and guidelines to successfully complete the marker aided introgression of one allele/haplotype from one breed to another, provided now by the "InSure" package.

Further research

The pathogen specificity and possible effects on mammary gland gene expression of the QTL alleles will be further studied within the Integrated project Cutting Edge Genomics for Sustainable Animal Breeding (SABRE), funded under the 6 th Framework Programme. The other two fine-mapped QTL regions affecting mastitis and somatic cell scores may be further analysed in an effort to identify disease-associated haplotypes. The material (identified segregating families and medium dense maps) to analyse the remaining chromosome regions showing evidence for containing loci affecting mastitis resistance is also available for further research. This research could be realised either by the consortium partners or a wider community (including new breeds).

QLK5-CT-2002-01186, MASTITIS RESISTANCE
New breeding tools for improving mastitis resistance in European dairy cattle

Project Coordinator:
Johanna Vilkki
Animal Genomics
Biotechnology and Food Research
MTT Agrifood Research Finland
31600 Jokioinen
Finland
Email: Johanna.vilkki@mtt.fi
Tel: +358-3-41883669
Fax: +358-3-41883618

Website: http://www.agronet.fi/mastitisresistance

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