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Bacterial survival in sheep flocks: understanding the persistence and transmission of intramammary pathogens

Project Supervisors: Professor Laura Green, Dr Kevin Purdy, Dr Ed Smith - University of Warwick

Non-academic partner: Dr Liz Genever - AHDB Beef & Lamb

Project title: Bacterial survival in sheep flocks: understanding the persistence and transmission of intramammary pathogens

Project outline:

Endemic and chronic bacterial diseases are a major health and welfare issue for both humans and animals. This project, developed through the collaboration of veterinary epidemiologists, microbial ecologists and industry, will address key questions in disease persistence. The successful student will develop skills in microbiological and molecular analysis of pathogens in the laboratory and epidemiological skills at the desk; and gain expertise in complex microbial infections and infectious disease epidemiology.


Acute clinical mastitis, defined as an inflammation of the mammary gland, usually caused by a bacterial infection, affects up to 6.6% of ewes each year; and probably as a result of this, up to 40 % of ewes develop intramammary abscesses. Mastitis is endemic in the UK, and considered the most important disease affecting suckler ewes. Costs to the sheep industry attributable to mastitis have been estimated in excess of £120 million/annum, which clearly impacts on farm sustainability. A reduction in milk yield and quality has knock-on effects on lamb growth rates; and the disease also affects the welfare of affected ewes through pain, loss of udder function, premature culling and occasionally death.

More than 30 bacterial species have been associated with intra-mammary infections and chronic mastitis in ewes. Some bacterial species that cause mastitis spread from ewe to ewe, others come from the environment; and individual strains of a species can persist within a flock for a number of years. However within flock transmission routes remain uncharacterised.

This project will investigate the persistence and transmission of bacterial strains within flocks by addressing the following hypotheses:

  • Bacterial strains detected in milk from cases of clinical mastitis are detected in the milk of the same and other ewes later in lactation
  • Persistence of strains is enhanced by intramammary masses
  • Persistence of strains occurs within the ewe mammary gland across lactations
  • External factors, such as poor diet, trigger disease (acute mastitis) in infected sheep

In the first part of the project, milk samples collected from a targeted sample of sheep as part of a recent 2-year prospective study of 4,000 ewes conducted at Warwick, funded by AHDB Beef & Lamb will be analysed. The samples originate from 10 flocks that include both indoor and outdoor lambing, and this will permit the investigation of management approaches on within-flock pathogen survival and persistence. Results from this initial work will contribute to the design of a longitudinal study to test novel hypotheses that arise from the first stage of work.

Ultimately, the aim is to improve the management of mastitis and so improve sustainability of sheep farming through reduced economic impact of disease and increased ewe longevity by improved health and welfare.


  1. Arsenault J, et al. (2008) Prev Vet Med; 87:373-93. doi: 10.1016/j.prevetmed.2008.05.006.
  2. Mørk T, et al. (2007) Acta Vet Scand; 49: 23. doi: 10.1186/1751-0147-49-23
  3. Smith EM, et al. (2015) J Dairy Sci; 98: 7025-7033. doi: 10.3168/jds.2015-9702
  4. Omaleki L, et al. (2012) J Vet Diagn Invest; 24:730-4. doi: 10.1177/1040638712448186

Closing date for applications: 31st March 2016

Contact: For further information regarding the project, please contact Professor Laura Green

Check eligibilty and apply here

Please note:

iCASE students must fulfil the MIBTP entry requirements and will join the MIBTP cohort for the taught modules and masterclasses during the first term. iCASE students can then start their PhD project in Jan 2017 but must complete a 3-month miniproject (at a non-home institution) before the end of their first year. They will remain as an integral part of the MIBTP cohort and take part in the core networking activities and transferable skills training. MIBTP iCase.