Retrospective cohort study investigating the relationship between diarrhea during the preweaning period and subsequent survival, health, and production in dairy cows

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The primary objective of this study was to evaluate the association between preweaning diarrhea and measures of survival, health, and production. The measures of interest included survival (mortality before first calving and time to removal from the herd), health (retained fetal membranes, metritis, mastitis, and SCC), and production (305-d mature-equivalent milk yield and time to first calving). A secondary objective was to investigate if these associations varied according to the age of the calf when the case of diarrhea occurred. Herd records from a farm located in Southern Australia were used to conduct a retrospective cohort study where subjects (calves) with diarrhea were enrolled at the time of their first case along with 2 subjects without diarrhea, matched for age (±3 d) and date of birth (±15 d), amounting to 9,833 calves in the dataset. Survival analysis was conducted to determine whether preweaning diarrhea was associated with death in the short term (first 20 d after enrollment), medium term (21-100 d after enrollment) and long term (101 d after enrollment to first calving). Crude incidence rate ratios, Kaplan-Meier curves, and hazard ratios (HR, Cox regression) were derived for each event-based outcome (e.g., death, calving, mastitis). Multivariable linear models were used for continuous outcomes. Calves with preweaning diarrhea had greater mortality rates in the short term (HR = 2.48, 95% CI: 1.87-3.29) and medium term (HR = 1.89, 95% CI: 1.41-2.55), but not in the long term (HR = 0.98, 95% CI: 0.79-1.22). A small negative association between preweaning diarrhea and time to first calving was found, with calves with diarrhea calving 4 d later than calves without diarrhea (HR = 0.95, 95% CI: 0.91-1.00). Rates of postcalving removal from the herd (death or culling) were higher in calves with a history of preweaning diarrhea (HR = 1.13, 95% CI: 1.01 to 1.26), as were peak lactation log SCC (+0.08, 95% CI: 0.02 to 0.14). Further research is needed to replicate these novel findings, as they are based on exploratory analyses and could be spurious findings. No substantial associations were observed for the other measures of interest. Our study findings support existing research demonstrating the importance of preweaning diarrhea as a substantial cause of calf mortality and raise new hypotheses about other potential impacts during lactation.