Reproductive failure has a negative impact on livestock production, animal health and welfare and ultimately rural economies.
There are several potential underlying causes of reproductive failure and not all of these are known. However, there are many infections that have been clearly identified as causing abortion/stillbirth in cattle and sheep. Such infections include viruses (bovine viral diarrhoea virus, border disease virus, bovine herpes virus, bacteria (Chlamydia abortus, Campylobacter fetus, Listeria monocytogenes, Bacillus licheniformis) and protozoa (Toxoplasma gondii, Neospora caninum). All of these infections are endemic in the UK and affect livestock farmers by reducing productivity in cattle herds and/or sheep flocks. Some of these infections cause abortion/stillbirth when they are acquired for the first time in animals that are already pregnant. However, some infections can be acquired by animals before they are pregnant and persist in a subclinical state.
Notable examples of these are N. caninum in cattle and C. abortus in sheep. Persistently-infected animals may be difficult to identify since they do not show overt signs of disease. They therefore represent an effective way for these pathogens to survive within a herd or flock.
To develop better control strategies for these infections, it is important to understand how the organisms cause disease (pathogenesis), identify what type of immune response control the infection, and investigate what changes in the immune response occurs during pregnancy that result in a sub-clinical infection manifesting as abortion/stillbirth.
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