Abamectin, a member of the Ivomec family is the active ingredient in a lot of cattle drenches (pour-ons, injections and oral products).
With the proliferation of drenches containing this chemical, reports have emerged of deaths in younger cattle that have been overdosed with these drenches (normally low dose formulations with high concentrations of abamectin).
As a rule of thumb, we would recommend that you do not use any product containing abamectin on young or light cattle under 150kgs (especially oral formulations). Always read the label and dose to the correct weight! The correct dose at 1ml per 20kg for pour-on formulations for a 200 kg animal might not seem much, but it is enough. You don’t need to give it another squirt to be sure!
As an aside I also read a recent report where dairy cows died when drenched orally with a cattle pour-on! Another good reason to always read the label and never leave drenches in unlabelled or wrongly labelled containers!