Horses which have been treated with phenylbutazone or 'bute' are not allowed to enter the food chain. The 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 sheep and cattle, etc.
The FSA also carries out regular enhanced sampling and testing for phenylbutazone in meat from horses slaughtered in the UK.
– FOOD STANDARDS AGENCY
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 (FSAI) checked for the presence of phenylbutazone and the samples came back negative.