-          Ovulation is produced into last third of the estrous period.

-          Ovulation starts 30 – 40 hours after estrous begining.

-          Ovulation lasts 12 hours.

-          Viability of spermatozoa into the oviduct is around 24 to 36 hours

            Generally speaking, six different cases can be found:

1.      Weaned sow with a normal heat

2.      Weaned sow with a late heat

3.      Cyclic returned sow

4.      Acyclic returned sow

5.      Primiparous sow with a normal heat

6.      Primiparous sow with a late heat

Case 1. Making two heat detections per day, insemination starts at 12 hours from heat detection, making the second one at 24 hours from the first. If the sow stays in head for third day, it is inseminated again, 12 hours after the second insemination (it is possible that there is not a fourth insemination)

Cases 2. 4. 5. 6. All these cases are abnormal, except Case 5, that is included here because it has a shorter heat. In all these cases, we inseminate just in the moment of the heat detection and if it is possible every 12 hours, because the heat may be short. 

Case 3. In this case it is possible that heat detection failed, or that semen dosis was not in good quality conditions, therefore, the sow not being the problem. It is necessary to study the case (boars data ). If the problem does not come from the sow, we start to inseminate just in the moment of the heat detection, but we can perform the second insemination 24 hours later. If there is a third, we will make it 12 hours after the second one.