The premises of a feed producer were raided late last week as part of the inquiry.
A spokesperson for the Dutch food safety authority, nVWA, told this publication today that food safety inspectors have suspended operations at about 100 Dutch pig and veal farms that had taken delivery of feed contaminated with the antibiotic.
He added that around 2,450 animals will have to be culled as part of the investigation, as “tests have revealed the presence of residues” of the illegal substance in the livestock.
The spokesperson said he could not comment on whether the latest farm closures are linked to the discovery last month of furazolidone-tainted feed on five farms in Gelderland.
In that case, the prohibited substance had been detected at a dairy farm that had supplied feed to four veal operations. All five farms have also been shut down by the authorities pending further investigation.
Detection through routine monitoring
The detection of Furazolidone in feed in the Gelderland area was uncovered when routine monitoring by the Dutch veal accrediting body, SKV, found an irregularity in a urine sample, said the nVWA.
The SKV had notified the food safety agency, as the national authority, of its discovery.
The Dutch veal sector has mandated SKV inspectors to carry out unannounced inspections at affiliated producers of veal feed, animal feed traders, veal farms and slaughterhouses in a bid to ensure high quality standards in the veal supply chain.
Dosage levels
In relation to the Gelderland contamination incident, the nVWA said the levels of Furazolidone involved were higher than the acceptable dose but it added there was no risk to public health.
The agency said that calves tested had between 0.2ug and 40ug of the breakdown product of the antibiotic, 3-amino-2-oxazolidinone (AOZ), in their meat.
If meat was regularly eaten at the average level of contamination, this would result in average human exposure of 1.2ug per person per meal, said the nVWA.
The World Health Organization (WHO) says that an unacceptable risk for consumers would be an AOZ exposure level of 3ug per day over a lifetime.
Illegal antibiotic usage
The nVWA told us the use of illegal antibiotics in feed in the Netherlands is not common. “This case is highly unusual for the Dutch livestock sector. The use of banned substances in feed is extremely rare."
In August 2012, the Dutch authorities seized 1,000 kg (2,205lbs) of illegal antibiotics that may have been meant for use as growth promoters in animal feed.
The cargo of virginiamycin, an antibiotic that has been banned for feed use by the EU since 1998, was found during a search of a shipping company in the southern Netherlands.