Defleecing effect of betamethasone and other long-acting corticosteroids, their influence on wool growth and some physiological processes in sheep.

The defleecing effects of the long-acting derivatives of prednisolone, triamcinolone and dexamethasone were compared with those of betamethasone alcohol when these steroids were administered at the rate of 3.3 mg/kg liveweight in three equal intramuscular injections of 1.1 mg to Merino wethers. Prednisolone showed no defleecing activity whereas the other steroids produced positive but variable responses. Prolonged depression of wool growth was evident following treatment with dexamethasone esters. Betamethasone alcohol injected intramuscularly at 1.1 mg/kg daily for 3 days produced a similar defleecing response to intravenous infusion of 3.3 mg/kg betamethasone phosphate over 8 days. A range of dose rates (0.3-3.3 mg/kg) of betamethasone as multiple and single intramuscular injections indicated that the minimum effective defleecing dose was approximately 2.1 mg/kg. The response to simultaneous administration of betamethasone and insulin or chlorpropamide (to increase glucose utilization) and glucose or xylazine (to increase hyperglycaemia) suggested that the gluconeogenic role of this steroid had little effect on fibre shedding. Thyroxine (300 micrograms per sheep) administered on the first day with an injection of betamethasone (0.9 mg/kg), and alone daily for 20 days thereafter, did not influence the changes in wool production resulting from betamethasone treatment. These results are discussed in relation to the molecular structure and physiological characteristics of a potentially specific defleecing steroid.