Relationship between herd calving to conception interval and culling rate for failure to conceive

The factors affecting herd calving to conception intervals and culling rate are the interval to first service, the efficiency of heat detection, the pregnancy rate and the maximum number of oestrous cycles allowed to occur before the cow is considered to be so far into lactation that even if it does conceive, the length of the dry period and the delay to the next calving will make its production uneconomic. Depending on the fertility factor (the product of the average herd pregnancy rate and the oestrus detection rate) it is the maximum number of oestrous cycles, usually dictated by the length of the calving interval desired, that decides the outcome. A graphical representation of these mathematical relationships demonstrates methods for achieving different economic and other objectives.