Ovulation in the sow occurs about two thirds of the way through the oestrus cycle and insemination must occur a few hours prior to this. There is no perfect timing that suits all farms, or all sows, so each farm will need to develop its own insemination strategy. It is therefore important to recognise the signs of heat and to act in accordance preferably keeping detailed records of heat detection. Those records will indicate if the herd has a 2 or 3-day standing heat. This can be used to plan an insemination routine on farm.

Accurate heat detection is essential for the correct timing of insemination. Ideally, heat should be detected twice daily with heat typically expected some 4-5 days after weaning. A good practice is to detect first thing in the morning and early afternoon in the presence of a boar for optimal stimulation. The main sign of heat is the standing reflex to back pressure. Most sows weaned on the same day will typically be synchronised, but do allow for some females to come on heat at different times after weaning. External factors such as seasonality (earlier oestrus in spring against later oestrus in autumn) will add to this variation.

The first insemination should be carried out 12 hours after the first standing reflex was detected (it may need to be a shorter or longer interval if the sow comes on heat later or earlier than 4 days post-weaning). The following diagram gives an example of timing of inseminations according to expected ovulation period. This particular example, where standing heat lasts 48 hours, shows ovulation occurring at about 32 hours from the onset of heat. Ovulation always occurs two thirds of the way through standing heat (no matter how long is the heat period).

It is good practice to use coloured markers to identify the insemination status of a sow or gilt. This give a visual indication to other stockmen of the next action for that animal. Optimal serving practices are easy to plan on farms with good records. The following list gives an indication of important parameters to record for each female on the farm: Tag or tattoo number, Date and duration of oestrus, Date and time (am/pm) of inseminations, ID of the semen inseminated, 3 week date, last return date(s), projected and actual farrowing dates, any other observations e.g. bleeding during/after inseminations, abortions etc.

In theory, if one could predict the exact time of ovulation, one insemination would be enough to obtain optimal fertility. Since significant variation can occur within the herd, two inseminations is a strict minimum for a successful service (some producers prefer 3 inseminations am/pm/am or pm/am/pm). The insemination doses should contain from 2.5 to 4 billion spermatozoa and follow strict standards for quality of the semen and storage of the doses prior to the insemination procedure.

Never inseminate a sow or gilt that is not in standing heat. Carrying out multiple inseminations over the standing heat period will maximise the success of your service.

September 2006

First published in International Pig Topics AI Star 5