Dexamethasone ester treatment alters insulin-like growth factor-I, its binding proteins and thyroid status in finishing calves

To improve carcass quality in finishing calves, some breeders use preparati ons containing corticoids alone or in association with other growth promote rs. We have investigated the effects of dexamethasone treatment on insulin- like growth factor-I (IGF-I), IGF-binding proteins (IGFBP-2 and 3) and thyr oid hormones (T-3, T-4, free T-4). Limousine male calves were allocated to a control group (C) (n = 18) and a group (n = 18) that received dexamethaso ne esters (DEX). Blood and hepatic tissue samples were collected at slaught ering. Thyroid hormones and IGF-I plasma levels were measured by RIA and IG FBPs were evaluated by immunoblotting. Hepatic type I 5'deiodinase (5'D-I) activity was determined by enzyme assay and hepatic expression of mRNA for GH receptor, IGF-I, IGFBP-2, IGFBP-3 and type I deiodinase (D-I) was evalua ted by dot blot analysis. Plasma IGF-I and IGFBP-3 levels were reduced by t he DEX treatment (P < 0.001 and P < 0.01, respectively) while IGFBP-2 was u naffected. Significant plasma changes for IGF-I and IGFBP-3 were not corrob orated by hepatic mRNA levels, for which only a slight non-significant decr ease was noted. Growth hormone receptor mRNA expression was increased after treatment (P < 0.01). T-3 plasma level was higher in DEX animals (P < 0.05 ) than in C calves. Finally, treatment increased 5'D-I activity in the hepa tic tissue (P < 0.001) and seemed to also affect D-I mRNA expression (P = 0 .1). In conclusion, dexamethasone ester injection in calves altered some of their endocrinological parameters; this could explain the catabolic action of corticoids in the bovine species.