Istituto Zooprofilattico Sperimentale delle Venezie, viale dell'Università 10, 35020, Legnaro, PD, Italy.
BMC Vet Res. 2012 Aug 3;8:129. doi: 10.1186/1746-6148-8-129.
Corticosteroids are illegally used in several countries as growth promoters in veal calves and beef cattle, either alone or in association with sex steroids and β-agonists, especially at low dosages and primarily through oral administration, in order to enhance carcasses and meat quality traits. The aim of the present study is to evaluate the reliability of the histological evaluation of the thymus, as well as the serum cortisol determination, in identifying beef cattle, treated with two different dexamethasone-based growth-promoting protocols and the application of different withdrawal times before slaughter.
Our findings demonstrate that low dosages of dexamethasone (DXM), administered alone or in association with clenbuterol as growth promoter in beef cattle, induce morphologic changes in the thymus, resulting in increase fat infiltration with concurrent cortical atrophy and reduction of the cortex/medulla ratio (C/M). In fact, the C/M value was significantly lower in treated animals than in control ones, with both the protocols applied. The cut off value of 0.93 for the cortex/medulla ratio resulted to be highly effective to distinguish control and treated animals. The animals treated with DXM showed inhibition of cortisol secretion during the treatment period, as well as at the slaughterhouse, 3 days after treatment suspension. The animals treated with lower doses of DXM in association with clenbuterol, showed inhibition of cortisol secretion during the treatment period, but serum cortisol concentration was restored to physiological levels at slaughterhouse, 8 days after treatment suspension.
The histological evaluation of thymus morphology, and particularly of the C/M may represent a valuable and reproducible method applicable to large-scale screening programs, due to the easy sampling procedures at slaughterhouse, as well as time and cost-saving of the analysis. Serum cortisol determination could be considered as an useful in vivo biomarker of dexamethasone illegal treatment in beef cattle during the fattening period, whilst it does not appear to be a good biomarker at the slaughterhouse, since the protocol of DXM administration, as well as the withdrawal period could affect the reliability of the method.
在一些国家，皮质类固醇被非法用作小牛肉和肉牛的生长促进剂，单独或与性激素和β-激动剂联合使用，特别是在低剂量下，并主要通过口服途径使用，以提高胴体和肉质特性。本研究的目的是评估组织学评估胸腺的可靠性，以及血清皮质醇的测定，以识别用两种不同的基于地塞米松的生长促进方案治疗的肉牛，并在屠宰前应用不同的停药时间。
我们的研究结果表明，低剂量的地塞米松（DXM），单独或与克伦特罗联合作为生长促进剂用于肉牛，会引起胸腺的形态变化，导致脂肪浸润增加，同时皮质萎缩和皮质/髓质比（C/M）降低。事实上，在用两种方案处理的动物中，C/M 值均明显低于对照组。皮质/髓质比的截断值为 0.93，可有效区分对照组和处理组。用 DXM 处理的动物在治疗期间以及停药后 3 天在屠宰场均表现出皮质醇分泌抑制。用较低剂量的 DXM 与克伦特罗联合处理的动物在治疗期间表现出皮质醇分泌抑制，但在停药后 8 天，血清皮质醇浓度恢复到生理水平。
胸腺形态学的组织学评估，特别是 C/M，可能是一种有价值且可重复的方法，适用于大规模筛选计划，因为在屠宰场取样程序简单，分析省时省力。血清皮质醇测定可作为在育肥期间牛用地塞米松非法处理的有用的体内生物标志物，但在屠宰场似乎不是一种很好的生物标志物，因为 DXM 给药方案和停药期可能会影响该方法的可靠性。
