Fenbendazole 150 is a widely used dewormer in horses and has been trusted for many years to control internal parasites. It belongs to the benzimidazole class of anthelmintics and works by disrupting the parasites&rsquo; ability to absorb nutrients, ultimately causing them to die. While it can be effective, its overall performance depends on several important factors.<br style="box-sizing: border-box; color: rgba(0, 0, 0, 0.87); font-family: 'Open Sans', Tahoma; font-size: 16px;" /><br style="box-sizing: border-box; color: rgba(0, 0, 0, 0.87); font-family: 'Open Sans', Tahoma; font-size: 16px;" />However, in recent years, resistance has become a significant concern. Many horse populations have developed resistance to fenbendazole, particularly small strongyles (cyathostomins). This means that in some cases, the medication may not be as effective as it once was. Because of this, veterinarians often recommend performing fecal egg count tests before and after deworming to determine whether the treatment is working properly.