Are parasite problems returning in cattle due to dewormer resistance?

Dewormers (anthelmintics), when given correctly, are not killing intestinal parasites of cattle as they used to. Although new drug “classes” entered the market from the 1950s to the 1980s, it has now been over 40 years since ivermectin was introduced in 1981. Basically ‘we have what we have’ which is 3 major chemical classes or families of dewormers known as the Benzimidazoles (SafeGuard® & Panacur®/ Valbazen®/Synanthic®), the Macrocyclic Lactones or MLs (Ivomec®/ Cydectin®/ Eprinex® & LongRange®/Dectomax®/generic ivermectins) and the Imidazothiazoles/…