Role of Infection and Immunity in Bovine Perinatal Mortality: Part 1. Causes and Current Diagnostic Approaches

SIMPLE SUMMARY: Death of calves before, during and up to 48 h after birth is referred to as bovine perinatal mortality (PM). This is caused mainly by calving problems. However, some cases of PM are caused by infections (pathogenic microbes). Infections include bacteria, viruses, parasites and fungi, and in some cases, multiple pathogens. Diagnosis of infection as a cause of PM can be difficult as one needs to differentiate between exposure to the pathogen, infection by the pathogen and the pathogen causing PM. Most cases of PM attributed to infection are caused by infections acquired in utero. Investigation of infectious PM involves collecting a health history of the dam, the calf and their herd, post-mortem examination of the dead calf and its placenta and collecting appropriate samples for laboratory testing. ABSTRACT: While non-infectious causes are more commonly diagnosed in cases of bovine perinatal mortality (PM), the proportion caused by infections is highly variable between studies (~5–35%); the reasons for this variation, and possible underestimation, are discussed. The most important pathogen-specific infectious causes of PM are bacteria (in particular, Bacillus licheniformis and Leptospira spp.), viruses (in particular BVDv) and a parasite (Neospora caninum). However, co-infection may occur in a small proportion of cases and in many cases no single pathogen is detected but gross or microscopic lesions of an inflammatory response are identified. Diagnosis is complicated by the criteria required to establish exposure, infection and causation. Additionally, pathogens can be classified as primary or secondary though such differentiation can be arbitrary. The majority of infectious cases of PM are due to in utero infections but postnatal infections (0–2 days) can also cause PM. Diagnosis of infectious PM is based on a systematic investigation of the herd health history and dam and cohort sampling and examination of the perinate and its placenta. Gross and histopathologic examinations and maternal/herd and perinate serology form the basis of current infectious PM investigations.