It is one of the biggest swill busts in NSW, according to Primary Industries Minister Ian Macdonald.

NSW Department of Primary Industries agricultural compliance manager, Andrew Sanger, said the pigs were being allowed to feed on dead sheep as well as other animal carcasses including pigs and poultry from the Forbes properties.

"The three men involved in the swill feeding racket are brothers Stephen Mark McConnell, Grahame Mark McConnell and William Arthur McConnell," he said.

"They were charged with 14 offences related to feeding prohibited substances to stock and failing to prevent stock from having access to prohibited substances (carcasses)."

The NSW DPI and the local Rural Lands Protection Board investigated the case and brought it before the court as a breach of the Stock Diseases Act.

Dr Sanger said the seriousness of the offences can not be overstated.

"Swill feeding is illegal," he said.

"Activities like this increase risk of spreading a number of endemic diseases like Anthrax, and have the potential to cause exotic disease outbreaks such as foot and mouth disease.

"Throughout the horse flu outbreak we saw first-hand the devastation exotic disease can cause.

"Diseases associated with swill feeding animals have the potential to cause massive disaster for our livestock industries through loss of export markets, lost production and large-scale animal health and welfare issues."

The men were fined $19,000 and ordered to pay court costs of $13,980.

Swill feeding has caused foot-and-mouth disease outbreaks overseas, including the catastrophic epidemic in the United Kingdom in 2001.

It was common in Australia in the 1950s and is now banned nationwide.

Some food wastes have been categorised as 'prohibited substances', and it is against the law to feed them to pigs.