Exploration of the prevalence and production impact of Mycobacterium avium subsp. paratuberculosis (MAP) infection in the sheep populations of Great Britain and New Zealand.

Mycobacterium avium subspecies paratuberculosis (MAP) is a prevalent, obligate pathogen of many wild and domestic species with a global distribution. MAP prevalence, epidemiology and production impact has been extensively studied in cattle whilst comparatively little research has been conducted on sheep. The aim of this project was to assess the prevalence of MAP in Great Britain (GB) and New Zealand (NZ) using faecal PCR and describe the relationship between MAP faecal shedding, reproductive failure (as determined by ultrasound pregnancy diagnosis) and longevity. A total of 162 farms in GB and 76 in NZ were sampled using a combination of individual and pooled faecal sampling frames of which 70 % of GB flocks and 88 % of NZ flocks tested positive for MAP. MAP shedding was associated with a 3 times increased risk of reproductive failure and significantly higher flock replacement rates in infected flocks. Reproductive failure is an important cause of forced culling in commercial flocks, leading to higher replacement rates and reduced lifetime output per breeding ewe. Excess culling and replacement costs due to preventable infectious disease reduce flock productivity, profitability and negatively impact sustainable lamb production. Effective control measures are available for MAP infected flocks but adoption is hampered primarily, but not exclusively, by poor recognition and underdiagnosis of the disease coupled with a poor awareness of the production limiting nature of the pathogen at the flock level.