Return to oestrus

When the sow is mated but it does not become pregnant, we say that it has "returned to oestrus" (it repeats a heat). Normally, we will notice that some of the sows that have been mated are not pregnant because 21 days later they are in heat again (they "returns"). The way to calculate the return to oestrus rate is as follows:

Number of returns to oestrus during a certain period of time         
______________________________________________________  x 100

Total Matings during the same period of time