Monitoring of health disorders during early lactation is a key component in the management of dairy systems. Electronic systems that allow for monitoring of rumination are now available. The objective was to evaluate the association between changes in rumination time (RT) and early stages of disease within the prepartum and early lactation. Two weeks before the due date, 198 cows at the University of Florida (UF) Dairy Unit were affixed with a neck collar containing rumination loggers (Hr-Tag rumination monitoring system, SCR Engineers Ltd., Netanya, Israel), providing rumination time (RT) for each 2-h interval. Occurrence of health disorders [mastitis (MAS), metritis (MET), clinical hypocalcemia (HYC), digestive disorders (DIG), lameness (LAM), and ketosis (KET),] were assessed until 60 DIM by UF veterinarians and farm personnel. Two indices were developed to explore the association between RT and disease: i) Cow Index (CI) = 24-h RT on the day of diagnosis (d0) minus average RT on d −3 to −5 relative to d0 (0to3–5RT), divided by the −3 to −5 d RT average; ii) Mates Index (MI) = (0to3–5RT - pen mates 0to3–5RT)/pen mates d0 RT. Subsequently an alert value (ACI and AMI) was determined for both indices when the value was lower than −0.1. Alert indices were evaluated by ROC curve analyses. Average CI in healthy cows ranged from 0.0491 to 0.0495 while CI in sick cows were −0.165, −0.029, −0.513, −0.022, −0.098, and −0.081 for MAS, MET, HYC, DIG, LAM, and KET, respectively. Average MI in healthy cows ranged from 0.0001 to 0.001 while MI in sick cows were −0.183, −0.101, −0.424, −0.101, −0.148, and −0.147 for MAS, MET, HYC, DIG, LAM, and KET, respectively. Sensitivity/specificity (%) of ACI were 56/72, 39/73, 100/72, 44/72, 67/72, and 61/72 for MAS, MET, HYC, DIG, LAM, and KET, respectively. Sensitivity/specificity (%) of AMI were 63/71, 42/72, 100/72, 48/72, 55/72, and 67/72 for MAS, MET, HYC, DIG, LAM, and KET, respectively. Area under the curve for our proposed cut-off value ranged from 0.56 (KET) to 0.87 (HYC) for CI and from 0.51 (MET) to 0.87 (HYC) for MI. Consistent negative changes in rumination activity, both within cow (CI) and compared with cohorts (MI), were observed on the day of diagnosis for each postpartum disease.