Survival analysis of the effects of type of calving on days from calving to conception, calving interval and number of days on the farm based on Kaplan-Meier method, log-rank test and multivariable Cox regression modelling

Days from calving to conceptionCalving interval (days)Survival on farm (days)
Number of observations included in the analysis264316845759
Kaplan-Meier estimated median±sePTC group103±2.6388±2.8750±48.9
FTC group110±1.8395±2.5529±21.1
Log-rank testType of calvingP=0.02P=0.29P<0.01
Multivariable Cox regressionCalving yearP<0.01P<0.01P<0.01
Calving month–*–*P<0.01
Stage of lactationP<0.01–*P<0.01
Milk yieldP<0.01P<0.01P<0.01
Type of calvingP=0.13P=0.32P<0.01
Adjusted HR (95% CI) of PTC v FTC in multivariable Cox regression1.07 (0.98 to 1.16)1.05 (0.95 to 1.17)0.86 (0.78 to 0.94)
  • *Calving month was not included in the multivariable analysis of days from calving to conception (P=0.40); calving month (P=0.33), parity (P=0.13) and stage of lactation (P=1.00) were not included in the multivariable Cox regression for calving interval.

  • CI, confidence interval; FTC, full-term calving; HR, hazard ratio; PTC, preterm calving.