Necropsy-Based Analysis of Causes of Neonatal Mortality in Dairy Calves in Poland.

The aim of this study was to identify the main causes of neonatal mortality in dairy calves (0-30 days of age) in Poland and to assess how infectious factors and management practices influenced the pattern of mortality. A retrospective analysis was performed on 498 calves from 312 herds between 2018 and 2024. The protocol included necropsy, enteropathogen diagnostics (PCR and ELISA), and analysis of herd management questionnaires. The leading causes of death were chronic diarrhea (42.4%), acute diarrhea (25.3%), and septicemia (10.8%). Calves that died from septicemia were the youngest (mean age 7.7 days), whereas those that died from chronic diarrhea were the oldest (20.3 days; p < 0.001). Lack of dam vaccination was associated with a higher occurrence of acute diarrhea (RR = 2.04) and septicemia (RR = 2.01) within the necropsied calf population. Inappropriate colostrum management was also associated with a higher occurrence of septicemia (RR = 1.99). Despite widespread antimicrobial use (>80%), intensive fluid therapy was used rarely (<7% in diarrheal cases). ETEC, rotavirus, and coronavirus were detected significantly more frequently in acute diarrhea, whereas Cryptosporidium parvum (C. parvum) was significantly more frequent in chronic diarrhea. Antimicrobials were used extensively, while intensive fluid therapy for diarrhea was implemented infrequently and inadequately relative to disease severity. This study makes an important contribution to the understanding of calf mortality in dairy herds by combining comprehensive postmortem diagnostics with pathogen detection (PCR and ELISA) and the assessment of management practices, thereby providing a holistic perspective on the problem. The analysis of 498 calves from 312 farms over a 7-year period offers an unprecedented and representative picture of the situation in Poland, one of Europe's major milk producers. These results emphasize the crucial importance of proper colostrum management and vaccination, while also indicating a clear and urgent need to expand the use of fluid therapy in calves requiring treatment. The results identify not only the dominant pathogens and differences in disease course, but also management factors with direct implications for animal welfare and preventive strategies in dairy production.