Identification by a proteomic approach of a plasma protein as a possible biomarker of illicit dexamethasone treatment in veal calves.

Corticosteroids have become the most widespread illegal growth promoters in veal calves and beef cattle. Testing for corticosteroids relies on either direct detection of compounds or their metabolites or indirect detection to identify changes in biological pathways. We used a comparative proteomic approach, based on two-dimensional electrophoresis (2DE), to identify plasma protein markers after short-term dexamethasone administration in veal calves. Twenty-three male Friesian veal calves were treated experimentally with dexamethasone sodium phosphate: 10 received low-dose administration of the drug (0.4 mg day⁻¹ per os) for 20 consecutive days (treatment group); 10 received the drug at therapeutic dosage (2-4 mg kg⁻¹ i.m.) for 3 consecutive days (comparison group). Three animals were not treated (control group). Plasma samples were collected from each animal at six time points (T1-T6; treatment and control group) and at four time points (T1-T4; comparison group) and stored at -80°C until analysis. Plasma proteins were quantified and analysed in triplicate by 2DE. The images were analysed with Bionumerics® software. Comparison of 2DE maps obtained from blood samples at T1 (before treatment) and at T6 (final sampling) showed a significant disappearance (p < 0.001) of two protein spots at T6 in the treatment group. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis and immunoblotting identified these isoforms as serum paraoxonase/arylesterase 1 precursor (PON1). Synthesised in the liver and released into the blood, PON1 has an important role in lipid metabolism. The absence of variation of this protein in the comparison group suggests that the marker has good specificity for detecting illicit corticosteroid treatment.

Histopathology as a simple and reliable method to detect 17ß-oestradiol illegal treatment in male calves.

17ß-Oestradiol is a steroid hormone banned as a growth promoter in food-producing animals all over Europe because of its carcinogenicity. Despite mandatory monitoring of illegal treatment all over Europe, official analytical methods in use test negative a few days after 17ß-oestradiol administration, requiring new sensitive tools to ensure a high level of protection for consumers. The aim of this work was the evaluation of the accuracy of histopathology and immunohistochemistry for progesterone receptor (PR) as a screening method for the detection of low-dosage illegal treatments with 17ß-oestradiol. Fresian male calves (153) were farmed under controlled conditions, and 89 of them were treated with 17ß-oestradiol (5 mg/animal once a week for 4 weeks). After 15 days of suspension, all animals were slaughtered and sexual accessory glands (prostate and bulbo-urethral glands) were sampled for histological examination and immunohistochemical staining with anti-PR antibody (clone hPRa 2). Microscopically 86 out of 89 bulbo-urethral glands showed mild to severe metaplasia, while mild metaplasia was observed only in 1 control. Eighteen out of 89 samples of prostate did not show metaplastic lesions. Immunopositivity for PR characterised all treated animals, while no signal was detected in controls. These findings show that metaplasia of the sexual accessory glands is a sensitive and specific parameter for illegal 17ß-oestradiol treatment in calves at the slaughterhouse, while the appliance of immunohistochemistry for PR can improve to 100% the accuracy of this highly reliable histological approach.

Development of an enhanced histopathological approach to detect low-dose dexamethasone illicit treatment in veal calves.

Dexamethasone is one of a number of synthetic corticosteroids illegally used to promote growth in food-producing animals. Since these low-level drug cocktails evade detection by currently available chemical methods, simple biological indicators that can aid in laboratory analysis are needed. In an attempt to devise an accurate biological method that could detect illicit drug treatment in food-producing animals, we characterized microscopic morphologic alterations of the thymus in veal calves administered low-dose dexamethasone versus control animals. For this purpose, 122 male calves were farmed for 6 months in controlled condition: 81 animals were orally administered dexamethasone (0.4 mg day(-1)) for 20 days during the sixth month and the remaining 41 were kept as control. Urine samples were collected systematically during the treatment period, the suspension period and at the slaughterhouse. All animals were slaughtered 10 per day starting from 10 days after the last dexamethasone administration and the thymus was sampled for histological examination. The difference between the two animal groups was evaluated by means of a non-parametric test of hypothesis. No residues were detected in the urines collected since the third day after the last administration, whereas morphometric analysis of the thoracic thymus revealed a significant decrease in the cortex:medulla ratio in the treated animals (p<0.0005). We can conclude that this histological approach offers encouraging prospects as a screening method to overcome current limitations in controlling growth promoter abuse.