As herd sizes increase there is an ever-greater focus by their managers on labour efficiency in terms of minimising the number of man-hours needed to complete the regular programme of inseminations. What every manager must realise, however, is that the most efficient AI system is the one that gives the required reproduction results by inseminating at the right moment. Top efficiency in the mating house is not reached by skipping a routine of twice-daily checking of sows that are coming into heat! 

It is also not reached by using hormones in abundance. Inducing heat by hormones makes the selection of the most fertile sows more difficult and in the long run it can create problems in reproduction by giving rise to a lower rate of improvement.

Always and everywhere, the first insemination is most important. This means defining the correct moment to inseminate and trying to hit the target of conception in one shot.

A strategy of using the least number of inseminations per oestrus can be seen to be working successfully on many units. For example, it is a common practice at one herd with 450 sows where the non-conception rate is normally only about 5%. The farm has not had any repeat breeders at all in the last 2 months.

In the Netherlands the farrowing percentage after first insemination is going up and the number of inseminations per cycle is going down. With the least-number approach, most of the sows are inseminated only once. At the moment the average is around 1.6 inseminations per oestrus. A number of Dutch units are averaging just 1.2 inseminations per cycle, yet they have farrowing rates of 90% or higher.

Many research studies around the world have proved that, in principle, you need only one good insemination of the sow in the period of 24 hours leading up to her ovulation. Clearly, a focus on having a single insemination per oestrus therefore demands that the moment of ovulation is known. This should not be difficult to arrange in theory, considering that ovulation takes place at two-thirds of the way through the total length of time the on-heat sow will stand to the boar or to back pressure applied by an attendant.


The length of oestrus becomes an important factor in the calculation. Two major influences on its extent are the farm and the sow!

Research has found a definite farm effect, in that the records for a particular herd will show oestrus length to have stayed relatively constant for all sows over a span of years. This has to do with the genetics present, the type of management, the layout and the way in which the producer works with his animals. The sow effect is well known to any herd operator. Quite simply, the earlier a sow comes into heat after weaning, the longer her oestrus period will last.

These are not just academic observations they can be applied in practice to make least-number AI a realistic option. Once the farm effect and the sow effect are determined for the herd, its insemination strategy can be determined. There is even computer software that has been specially developed for this purpose. It helps to define the best moment of insemination on the basis of information gathered from the herd's records over a limited period of 6 weeks.

The data it analyses cover the time between weaning and first detected oestrus, the day and time when oestrus ended and the day and time of mating. This builds into a view of the duration of the standing heat for all sows in the herd, from which to calculate the moment of ovulation (at two-thirds of the total oestrus length) and optimal insemination time (in the period of 24 hours before ovulation).

It has demonstrated its value by allowing several hundred herds to schedule AI more exactly and therefore use fewer inseminations. In turn this has enabled them to reduce the total man-hours employed in inseminating, without reducing the critical time spent on checks to see when weaned sow are in oestrus.