Epidemiologic approaches used in a herd health practice to investigate neonatal calf mortality

Epidemiologic methods were applied in an investigation into causes of neonatal mortality on a 1400-cow dairy in the southern San Joaquin Valley of California. A format for collation of information on birthdate and date of death was assembled into a matrix which improved conceptualization of the data and which simplified procedures for estimation of mortality rates. Contemporary and birth cohort life table methods, mortality density estimations and relative risk assessment were used to ascertain if there were high-risk groups of calves that could be identified by age, day-of-the-week born, day-of-the-week died and sex. During the outbreak of neonatal diarrhea on this dairy, female calves were found to have experienced an atypically higher rate of mortality (10.7%) than did males (5.3%). Calves of both sexes died between the ages of 9 and 19 days. In addition, the risk of dying was 11 times greater for calves born on Wednesdays than for those born on Saturdays. These findings formed the basis for recommended changes in management of neonatal calves on the dairy.