The trials also looked at semen concentration and semen pooling as well as semen age at insemination.

The research team conducted three trials over three units involved over three or more service batches.

A range of boars was used and the doses split between all three units.

The boars were rotated so they were used across all treatments.

Only sows standing on heat on Tuesday were eligible for the Semen Age Trial and the sows were allocated randomly.

The trial used flatpacks of semen that were not identifiable by treatment on-farm (only by colour Blue, Red or Green).

The trial used batch farrowing and the age of the semen ranged from 12 hours, to 24 hours and 48 hours old.

The sows were colour coded by treatment.

The second trial compared semen concentration and concentrations of 2.4 billion sperm and 3 billion sperm were use.

The third trial looked at the use of pooled semen compared to single boars.

The test comparing semen concentrations showed no significant difference in fertility and the test comparing pooled semen with single boars also showed no significant difference in terms of returns and piglets born alive.

In these two trials, however, the day of mating always had a significant effect.

The researchers are now questioning whether this is a semen effect - capacitation - or the processes sperm pass through to achieve fertilisation.

However, in the test to quantify the effect the age of the semen has on reproductive performance, the research team found that semen age does affect fertility but 'fresh' was not best.

Again the researchers questioned whether this result could also be related to capacitation.

"We need research that meets the UK's unique requirements," said PIC UK supply chain manager, Steve Furniss.

"Whether this is meeting the needs of Outdoors or Loose house environments or using batch systems or once per day oestrus checking."

He said the research needed included more information on the motility of the sperm, which it has been discovered does not necessarily mean greater fertility.

Now PIC has a range of new tests and studies it is to conduct to gain more clarity and information about the results of the trials that have already been conducted.