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Studies Step up Battle Against Illegal Growth Promoters

16 February 2010

Due to the economic benefits that can be gained from the use of illegal growth promoters in beef cattle, their illegal administration continues, writes TheCattleSite senior editor Chris Harris.

The administration of these drugs and growth promoters animals destined for beef production continues to be an enormous challenge to regulatory authorities charged with enforcing their ban.

A recent report by Mark H. Mooney and Chris T. Elliott from the Centre for Food: ASsured, SafE and Traceable food (ASSET), Institute of Agri-Food and Land Use, School of Biological Sciences, Queen's University Belfast, Northern Ireland delivered to the Advancing Beef Safety through Research and Innovation An international conference organised by ProSafeBeef. In Ireland last year shows that despite many recent analytical advances the effectiveness of approaches currently used to detect banned growth promoter administrations is compromised by the continued use of endogenous hormones and low dose chemical cocktails, and also by the limited number of samples which can be routinely analysed for drug residue presence.

In their report onBioCop: Biomarker profiling as a screening tool to ensure beef safety, the researchers say that alternative testing strategies with high-throughput screening capabilities may offer the potential for targeted confirmatory analytical analysis on only those samples suspected of being derived from illicitly treated animals.

They say that now the focus has turned to developing novel testing methods based not on the direct detection of specific drug residues but rather on indirect evidence centred on "perturbations to physiological activity" that arise from the administration of growth promoters.

BioCop is an EU 6th framework project aimed at developing new screening technologies to identify chemical contaminants in food.

Working on specific strands in this project they have attempted to identify markers in plasma that are representative of altered biological activity.

"Through the comparative analysis of plasma from experimentally treated and non-treated animals a range of biomarkers have been revealed which are reflective of changes induced by growth promoter administrations," the researchers say.

"Biosensor assay technology has been developed to enable measurement of a panel of these biomarkers whose profiles can be used to distinguish between control and treated animals."

This biomarker approach could find use as a tool to help identify the identification of herds illegally treated with growth promoting agents and help overcome new challenges, which currently circumvent existing testing methodology and promoting confidence in the integrity of the beef supply chain.

One other similar study on biomarkers released last year on the Evaluation of indirect biomarkers for detecting corticosteroids used as illegal growth promoters in beef cattle by M. Vascellari, DVM, G. Pozza, DVM, L. Poppi, DVM, K. Capello, R. Angeletti, L. Ravarotto, I. Andrighetto and F. Mutinelli, DVM, DiplECVP at Padova University looked at the histological status of the thymus, blood cortisol concentration and circulating neutrophil:lymphocyte ratio.

These were evaluated in 349 slaughtered beef cattle, to assess the potential of these parameters as indirect biomarkers of the illegal use of corticosteroids in meat production.

The livers of 20 of the animals were analysed chemically for residues of corticosteroids. The morphology of the thymus was examined for adipose tissue infiltration, cortical atrophy and 'starry sky' appearance, and on the basis of these characteristics, the animals were considered to be negative, suspected or positive for illegal corticosteroid treatment.

The animals considered to be negative had a mean cortisol concentration that was significantly higher (29 ng/ml) than that of the animals suspected for corticosteroid treatment (22 ng/ml).

Using the chemical analysis as the gold standard for identifying illegally treated animals, the histological examination of the thymus had a sensitivity of 100 per cent and a specificity of 85 per cent.

The samples that were positive by chemical analysis had cortisol concentrations of less than 2·0 ng/ml, whereas the mean cortisol concentration of the negative samples was 10·3 ng/ml.

Another study from Padova University in Italy, by Lisa Carraro, Serena Ferraresso, Barbara Cardazzo, Chiara Romualdi, Clara Montesissa, Flaviana Gottardo, Tomaso Patarnello, Massimo Castagnaro, and Luca Bargelloni looked at the Expression profiling of skeletal muscle in young bulls treated with steroidal growth promoters, searching for the presence of Dexamethasone.

The report says that Dexamethasone (Dex), alone or in association with oestrogens, is often illegally administered per os at very low-dosage as a growth promoter in beef cattle, with effects that are opposite to the muscle wasting and atrophy induced by repeated administration at therapeutic dosages.

Studies shown that the effect of Dex at therapeutic doses on skeletal muscle is an increase in the expression of GDF8 (myostatin) gene, a negative regulator of skeletal muscle mass.

The Padova study looked at the expression profiles of beef cattle muscle in animals treated with either Dex or Dex plus 17-ß estradiol (Estr) administered at sub-therapeutic dosage, against untreated controls.

"Data analysis demonstrates that the expression profiles were strongly affected by Dex treatment with hundreds of genes up-regulated with relevant fold-change, whereas seven genes were down-regulated including the myostatin gene," the study says.

"On the contrary, the number of differentially regulated genes was lower in response to the addition of Estr to the Dex treatment."

The report adds that differentially regulated genes were analysed to describe the effects of these treatments on muscle physiology, highlighting the importance of specific pathways (e.g. Wnt or cytokine signalling) and cellular processes (e.g. cell shape and motility).

The differences in the expression profile will allow the development of indirect bio-markers to detect illegal Dex treatments in beef cattle using quantitative RT-PCR, the researchers say.

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