Pharmaceutical giant Wyeth has pleaded guilty at the Dublin Circuit Criminal Court to four counts regarding the illegal exportation of waste.

More than 50,000 pigs had to be destroyed in Holland after waste water from the production of contraceptive pills at Wyeth's Newbridge plant ended-up in Dutch animal feed.

This morning's case before the Dublin Circuit Criminal Court dates back to 2002 - the year when some Dutch pig farmers noticed their sows had become infertile.

Many farms across Holland were subsequently shut down, after the infertile pigs were found to have the hormone MPA in their blood.

The Dutch Feed Industry organisation claimed it was 'one of the worst disasters in living memory' and cost the industry 'at least €100m'.

Investigations subsequently traced the hormone back to Wyeth Medica Ireland's Newbridge plant.

It was identified that hormone-laced waste water was being produced in the process of sugar-coating its contraceptive pills.

This material was given to Dublin-based Cara Environmental Technology, which shipped it to a Belgian company Bioland, which passed it on as treacle to Dutch feed companies.

Today, Wyeth pleaded guilty before Judge Patricia Ryan to 4 of 23 charges regarding four shipments of hazardous waste out of Ireland between September 2000 and November 2001.

These related to shipping without a certificate, using a waste contractor, Cara Environmental Technology Limited, which was not licensed to transport or dispose of that hazardous waste and engaging Cara who mixed the waste.

Cara Environmental Technology is due before the Dublin Circuit Criminal Court over the same issues.

In a statement Pfizer, which acquired Wyeth in 2009, said it had been seeking to resolve the case since then but could not comment further as legal action continued.