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expert reaction to MP’s claims about phenylbutazone and horse meat

Shadow environment secretary Mary Creagh said in Commons that horses slaughtered in the UK had tested positive for the carcinogen phenylbutazone, or ‘bute’.


Prof Sir Colin Berry, Emeritus Professor of Pathology at Queen Mary, University of London, said:

“The compound has rarely caused blood dyscrasias even on those who have taken a lot for many years.  The idea that you might get a clinically significant amount in horse meat even after therapeutic administration to the horse is, frankly, daft.”


Peter Jones, President of the British Veterinary Association, said:

“Phenylbutazone (Bute) is a painkiller that is also used in humans.  It has a licence for use in horses that have been identified in their passport as not being destined for the food chain. 

“A Maximum Residue Limit (MRL) in meat has not been established for the use of bute in food-producing species because of concerns regarding the toxicity of the metabolites which could reside in meat from treated animals.  Due to the lack of the MRL, bute is banned for use in food-producing species.  The tracing system of horses for the food chain should pick this up and any horse having been treated with bute should be removed from the food chain.  Unregulated horsemeat of unknown provenance (i.e. that which enters the food chain illegally) could have a risk of bute residue as it is a commonly used drug.”


Prof Chris Elliott, Director of the Institute for Global Food Security at Queen’s University Belfast, said:

“Phenylbutazone is a drug often used in horses to treat sore joints and aid recovery after fractures.  Research has shown that when humans or animals were exposed to high levels there were adverse side effects such as bone marrow toxicity.  Therefore it is not licensed for use in animals that go into the food chain.  There is a system in place in Europe which should identify when horses have been treated with the drug to prevent them going for food production but the effectiveness of this has been doubted by many. 

“Thankfully the residues of drugs such as phenylbutazone found in meat are very low and the risk to the consumer is correspondingly low.  However, the use of veterinary medicines in all animal species that do go into the food chain is a matter of food safety and has to be treated seriously. 

“In the UK & Ireland as well as all other EU member states there are systems in place to test samples of foods of animal origin of a wide variety of veterinary medicines.  In the vast majority of cases, however, this testing is in the raw materials – meat, eggs, fish etc – and not on processed foods.  This is a gap in the monitoring system which is in place to safeguard the consumer and authorities may feel the need to address this, particularly as we all consume so much processed foods these days.  

“In the present incident there is no evidence to suggest any residues of veterinary medicines were detected and indeed no evidence of any food safety related topic.”


Prof Alastair Hay, Professor of Environmental Toxicology at the University of Leeds, said:

“According to the International Agency for Research on Cancer (IARC), phenylbutazone is not classifiable as to its carcinogenicity.  There is no convincing evidence of its carcinogenicity in humans because in the individuals studied many other drugs had also been taken and any one of these might have caused the cancers seen.  And there is no animal evidence either that it is a carcinogen.

“The reason the chemical is not for human consumption appears to be rare and idiosyncratic responses in humans to the chemical.  These include aplastic anaemia and some other disorders of the bone marrow.  But these are not cancer events.”

Prof Hay has also provided a research paper for background.  It refers to the identifiable drug in horsemeat and the need to have proper screening processes in place to pick up the drug.


The Food Standards Agency has issued the following statement:

“The Food Standards Agency (FSA) carries out checks in slaughterhouses to ensure that horses presented for slaughter are fit for human consumption, in the same was as they do for other animals such as sheep and cattle. The FSA also carries out regular enhanced sampling and testing for phenylbutazone in meat from horses slaughtered in the UK.

“In 2012, the FSA identified five cases where horses returned non-compliant results. None of the meat had been placed for sale on the UK market. Where the meat had been exported to other countries, the relevant food safety authorities were informed.

“During the recent horse meat incident the Food Safety Authority of Ireland checked for the presence of phenylbutazone and the samples came back negative.”


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