In our study horn growth arrest following injection of clove oil essence in horn bud can be attributed to different mechanisms. It seems that existence of eugenol as a main component of clove oil can inhibit proliferation in horn germination cells and induce apoptosis in these cells. Also eugenol may have cytotoxic effect on cells in horn bud and consequently induce cell necrosis, as the histopathological examination in the present study confirmed it. Koger described a suitable and safe method for dehorning in calves including injection of calcium chloride as a necrotizing agent in horn bud. An overall success rate of 70% has been achieved in his study. The calves were sedated before injection and injection site were prepared aseptically. He stated that without tranquilization or anesthesia, injection of the necrotizing calcium solutions caused objectionable pain and strong physical restrain was necessary. In the current study, because of anti-inflammatory and analgesic effect of eugenol, we did not use local anesthetics and/or sedative drugs before injection and the animals were only physically restrained at the time of injection.