Infection exposure, detection and causes of death in perinatal mortalities in Polish dairy herds

- Exposure to pathogens during pregnancy as detected in approximately 21% of perinatal mortality calves.
- A humoral immune response was detected approximately twice as frequently as direct evidence of pathogen infection.
- Gestation length of infected singletons was significantly shorter than that of uninfected singletons.
- The most common infections in perinatal mortality calves, in descending order, were parasitic, viral and bacterial.

The objective of this study was to determine the prevalence and types of infections in perinatal mortality (PM) cases from Polish dairy farms and the relevance of the presence of infection to the cause of death. This prospective longitudinal study was carried out on 121 PM and 21 control calves with a gestation of ≥260 days. Six control calves were euthanized and examined using the same protocol as for PM calves. Material was collected over a 20-month period between November 2013 and June 2015. The PM and control calves were collected from 29 to 5 herds, respectively.Blood samples from calves were tested for antibodies to Neospora caninum, glycoprotein B of BoHV-1, BVDV and SBV using ELISAs and Leptospira hardjo and Leptospira pomona with the microscopic agglutination test. Brain and kidney samples from all PM and six euthanized control calves were tested using real time PCR to detect Neospora caninum, pathogenic Leptospira spp., BoHV-1 and SBV; brain was examined histopathologically for detection of N. caninum cysts. Samples from eight inner organs from all PM and six control calves were cultured aerobically, anaerobically and microaerobically. Ear samples from all PM and control calves were tested for BVDV using an antigen ELISA.In total, 21.5% of PM calves were infected (antigen and/or antibody-positive) in utero; none of the control calves were infected. Direct evidence of infection (culture, Ag-ELISA, PCR, histopathology) was detected in 9.1% of PM calves. Gestation length in infected singletons was shorter than in uninfected singletons (274 ± 8 vs. 279 ± 7 days; P < 0.01). The odds ratio for diagnosis of infection in single pregnancies ≤275 days was 3.75 (95% CI:1.2-12.1), (P < 0.05). Infection was the cause of death in 10% of calves. The most common infections detected in these Polish PM calves were parasitic (11.6% of PM cases), viral (7.4%) and bacterial (5%). This study demonstrated that indirect evidence of infection is detected more frequently than direct, coinfection is rare, infection is rarely accompanied by gross lesions and is rarely a cause of death in cases of PM.