A novel, illustrated classification system to define the causes of bovine perinatal mortality internationally

Currently there is no published classification system for the causes ofdeath in cases of bovine perinatal mortality internationally. In addition,the criteria used to define these causes of death are also not standardised,nor published. This results in inconsistent reporting of many differentcauses of death and often a high proportion of cases being unexplained.A system is required for codifying bovine perinatal mortality forepidemiological surveillance and perinatal audit, as in humanperinatology where the World Health Organisation's InternationalClassification of Diseases Manual is used internationally. Hence, theobjective of this study was to develop a novel classification system forboth the criteria and the causes of death in cases of bovine perinatalmortality internationally in order to improve our understanding of themain causes of such reproductive loss. A foeto-maternal, clinicopathologicalclassification system was developed over a period of threeyears using three primary sources of information. A systematic literature-based review, the findings of an international Delphi survey andepidemiological and pathological data from an active surveillance, wholeherdnecropsy study were used to design the system. Ten major causalcategories of death were assigned with sub-classification as required;alphabetically - combination of contributory factors (more than one causeof death), congenital defect (economically lethal and lethal), dystocia(bradytocia, traumotocia, bradytocia and traumotocia, dystociaanamnesis, dystoxia and fetal maldisposition), eutoxia, haemorrhage andanaemia (external omphalorrhagia, internal omphalorrhagia, idiopathichemoperitoneum, anaemia), infection, iodine imbalance, prematureplacental expulsion, prematurity and other specific disorders (e.g.accidental death, hypothermia, intra-uterine growth retardation, etc..).Each cause of death was assigned a degree of confidence of diagnosisfrom certain through probable to possible.These causes of death were assigned using the written anamnesisfrom the farmer or veterinary practitioner, gross necropsy observations(including photo-documentation) and the associated laboratory tests, i.e.an algorithmic, summary diagnosis. The cause of death indicated thepathological condition of the fetus or calf which made the greatestcontribution towards the death. Only proximate (immediate) factors werelisted in the cause of death, e.g. a genetic mutation may be the ultimatecause of a lethal congenital defect but the defect was the proximate causeof death. Some causes of death, e.g. dystocia, were disaggregated in orderto differentiate separate components (where a portmanteau is used, e.g.dystoxia) which can be re-aggregated as necessary for different reportingformats.Differential diagnoses were reached through both processes ofinclusion and of exclusion. This ten-level classification system can beused to calculate cause-specific mortality rates (CSMR) and theattributable fraction (AF) of perinatal mortality due to each cause of death.