Farmers are being urged to take extreme care when using the non-steroidal anti-inflammatory drug bute (phenylbutazone) to treat horses.
Investigative work carried out by scientists at the Agri-Food and Biosciences Institute (AFBI) has shown the risk of inadvertently contaminating cattle through the use of bute is very real.
“Following on from a number of positive findings in NI cattle, there was anecdotal evidence to suggest that, at least in some cases, the offending cattle may not have been illegally treated with the drug. In these cases, non-compliance may have arisen through contamination as a result of the legal treatment of horses on the farms.”Dr Steven Crooks, AFBI
Bute is an inexpensive, yet highly effective treatment for inflammation and pain that can be injected intravenously or given orally as a powder or paste to horses. It is not authorised for use in any animal, including horses, destined for the human food chain.
Despite this, official statistics provided by the European Food Safety Authority show that around 0.1% of cattle tested in the European Union in 2014 had detectable bute residues.
Horses treated with bute must not enter the food chain, and their passports must be signed to declare that the animal is not intended for human consumption. This is an irreversible decision.
In common with the EU results, testing for bute in cattle in Northern Ireland has, over the years, identified a small number of animals with detectable residues of the drug.
Dr Steven Crooks from AFBI explains: “Following on from a number of positive findings in Northern Ireland cattle, there was anecdotal evidence to suggest that, at least in some cases, the offending cattle may not have been illegally treated with the drug. In these cases, non-compliance may have arisen through contamination as a result of the legal treatment of horses on the farms.”
Based on this evidence, a number of studies were carried out by AFBI scientists to determine the likelihood that cross-contamination could be at the heart of at least some of the problem.
Studies undertaken by AFBI, using bute in its powder form, investigated the possibility of illegal residues in cattle arising through the use of a shared bucket (i.e. if a horse was to be fed from a bucket containing bute and then the same bucket used to feed cattle), a shared pen or through contaminated pasture.
In all cases results clearly demonstrated that contamination could in fact play a significant role. For example, cattle sharing the “dirty” bucket showed residues of the drug in their blood some 3,500 times greater than the lowest amount detectable using AFBI’s method of analysis.
Similarly, cattle sharing a pen with a treated animal, in this case an illegally treated bullock, demonstrated detectable concentrations within 24 hours of being penned together.
In the final study, a number of animals were treated with bute over the winter period. The manure and bedding from these animals was spread onto pasture in early spring and untreated cattle allowed to graze the pasture some 10 weeks later.
Subsequent analysis of blood from these grazing animals showed that all contained significant concentrations of bute.
Given that bute is often the drug of choice for horses and that many farmers do keep some horses, it is important that those using the drug take extreme care to avoid contamination of their cattle.
Dr Crooks explains: “While the therapeutic dose of the drug is high with, for example, a 450 kg horse receiving as much as 4 g of bute on the first day of treatment, a 130,000 times smaller amount (30 μg) of the drug can give rise to detectable residues in the blood of a 500 kg bullock.”
As such, extreme care must be taken to avoid any form of contamination of cattle as this will result in detectable residues which are costly, not only for the farmer, but also for the reputation of the Northern Ireland agri-food industry as a whole.