Does closantel in therapeutic doses display thyroid hormone‐like activity in sheep?

The aim of this study was to define the thyroid hormone‐like activity of closantel in sheep by measuring some blood parameters that are known to be influenced by thyroid hormones triiodothyronine (T3) and thyroxine (T4). Our hypothesis was that, if closantel possesses thyroid hormone‐like activity, its use under in vivo conditions will result in changes similar to those in hyperthyroidism. The study was conducted in 20 Jezersko‐Solchava breed sheep. Blood sampling was performed before and 10 days after routine anthelmintic treatment with closantel. Complete blood count, plasma cholesterol, triglycerides, protein, and albumin levels, as well as those of serum T3 and T4, were compared before and 10 days after closantel administration. This routine anthelmintic treatment of sheep with closantel did not significantly influence hematological parameters, thyroid hormone levels, or most of the biochemical parameters. No evidence was found for thyroid hormone‐like activity of closantel in sheep. However, significantly (P < 0.01) elevated levels of plasma triglycerides were present 10 days after closantel administration.