Thymus atrophy and regeneration following dexamethasone administration to beef cattle

Abstract

Thymus atrophy and regeneration were studied in 13- to 22-month-old beef calves treated with dexamethasone (DMT), using anabolic dosages and implementing different withdrawal times. Two trials were conducted. In trial 1, group A (n=6) received 0.7 mg/day DMT orally for 40 days, group B (n=6) received 1.4 mg/day orally for 40 days and group C (n=6) was the control. In trial 2, group D (n=6) received 0.7 mg/day DMT orally for 40 days, group E (n=6) received 1.4 mg/day orally for 40 days and group K (n=6) was the control. DMT withdrawal times before slaughter were six days (groups A and B) and 26 days (groups D and E). At slaughter, thymus atrophy was severe and progressive in animals from groups A and B. In contrast, thymus weight and volume of the animals from groups D and E were almost normal. Slight atrophy was also detected in the calves in these groups. Histological changes and Ki67 immunostaining revealed a large number of positive lymphoid cells, mostly in the cortical area, associated with higher expression of apoptosis in the medulla compared with controls. This demonstrated that the thymus of beef cattle is still able to regenerate following DMT administration.

Evaluation of thymus morphology and serum cortisol concentration as indirect biomarkers to detect low-dose dexamethasone illegal treatment in beef cattle

“…In addition, in beef cattle it is rather difficult to distinguish between physiological involution and treatment-induced atrophy, and the thymus score could be influenced by subjective inter-observer variations. Our data indicate that the severity of the histological alteration correlates with the administered DXM dosages, as previously observed [25]. In fact, among animals treated with lower doses of DXM in association with a β-agonist (group C), thymus atrophy was less evident than in group B, and many thymus samples were scored 2.…”

Morphological Examination and Transcriptomic Profiling To Identify Prednisolone Treatment in Beef Cattle

“…The usefulness of histological analyses on thymus morphology as a screening tool to identify illegal DEX treatments in cattle was already established [6][7][8][9][10] . On the contrary, gross and histopathological investigations on thymus were not useful to detect anabolic treatments with PDN in beef cattle 11 , and even gene expression profiling by DNA-microarray on thymus has revealed to be a weak tool 12 .…”

Hepatic tyrosine aminotransferase and glucocorticoid abuse in meat cattle

“…, 2011). While some groups have focused their attention on the histological changes occurring in target organs, most notably the thymus (Cannizzo et al. , 2008, 2010), others have investigated the GC‐mediated effects on blood leukocyte formula (Brambilla et al.…”

“…All the above reasons have prompted the researchers to develop reliable biomarkers for revealing the exposure to DEX or other GCs in cattle (Girolami et al, 2010;Nebbia et al, 2011). While some groups have focused their attention on the histological changes occurring in target organs, most notably the thymus (Cannizzo et al, 2008(Cannizzo et al, , 2010, others have investigated the GCmediated effects on blood leukocyte formula (Brambilla et al, 1998) or on blood cortisol levels (Vascellari et al, 2008). According to the legislation in force, a biological marker cannot replace an official analytical method, which represents the sole mean to prove the noncompliance of a given sample.…”