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

-          Ovulation starts 30 – 40 hours from the beginning of estrous.

-          Ovulation lasts 12 hours.

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

            In general, we can find six different cases:

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, the insemination starts at 12 hours from the heat detection, making the second insemination at 24 hours from the first. If the sow is in heat the third day, it is inseminated again, 12 hours after the second insemination (it is posible 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 posible that the heat detection has failed, or that the semen dosis was not in a good quality conditions, and therefore, the sow is not the problem. It is necessary to study the case (data of the boars). 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.