The Special Investigation Unit (Ireland) was set up to provide specialist inspectors within the Department of Agriculture to investigate and deal with practices relating to the use of illegal substances in animal production, such as was the case with the use of angel dust (clenbuterol) in the 1980s. Surveillance for the presence of residues of veterinary substances in food-producing animals is regulated by the Directive 86/469/EEC, which offers specific guidelines for sampling procedures on farms and in slaughterhouses. The category of compounds and species will determine the level and frequency of sampling and this is outlined in the NRCP each year. Sampling intensity increases in response to the incidence of non-compliant samples. This was evident during the bute horsemeat scandal in 2013 with intensified sampling for phenylbutazone in horses, which is a group A prohibited substance under Directive 96/23/EC (Annex I). This also occurred for anthelmintics in sheep/goats and dioxins in all species and food commodities.
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Analytical methods of detection have become more sensitive over time. This is due to the requirement to meet detection levels or MRLs outlined in legislation. For some substances, these have been lowered and methods must be sensitive enough to be able to detect very low concentrations of substances in multiple matrices. There are several analytical methods used for detection of drug residues in a sample. Enzyme-linked immunosorbent assay (ELISA) methods employed for this analysis usually target one substance and their cross reactants. This methodology works well as a screening tool for targeted screening. The disadvantage of using ELISA-based methods is in the event that a single sample needs to be screened for multiple drug residues since each drug residue has to be tested using a specific kit. The Siemens Immulite, which is an automated chemiluminescent immunoassay, is used for hormone detection such as progesterone and estradiol in serum samples. Again, as for the ELISA, an individual kit is required for detection of each individual hormone.
Randox Food developed another method of biochemical analysis using the Evidence Investigator. The Evidence Investigator biochip array technology (BAT) is used to perform simultaneous quantitative detection of multiple analytes from a single sample. The core technology is the Randox biochip, a device containing an array of discrete test regions containing immobilized antibodies specific to the drug residues under test—according to the kit type. The Evidence Investigator itself is a benchtop analyzer housing digital imaging instrumentation that captures the chemiluminescent signal emitted from drug residue conjugates labeled with HRP.
All of these methods are rapid, reliable, and sensitive. Drug residues or hormones may be detected in very small concentrations. The results obtained from analysis must be reproducible and all methods must be validated in accordance with the requirements of Commission Decision 2002/657/EC, which sets down standards for the performance of analytical methods and the interpretation of results.
An important area of focus in relation to residue testing is the dairy industry. Because milk and milk products, such as baby milk powder, are a huge export market for Ireland, it is important to screen these products for growth promoters and antibiotics. It is a legal requirement that raw milk not contain residues, including antibiotics. Each farmer is required to keep a record of all medicines purchased and administered to animals. Milk from dairy cows that are on antibiotic treatment must be discarded and kept out of the food chain until the withdrawal period has been observed. Milk testing programs employed by the dairy co-ops are tested at the farm level and have limitations. If antibiotics are detected, the milk must be discarded and not used for human consumption. Severe commercial penalties ensue for the farmer.