A unique, slow-release ear tag for cattle that is the first ever tag to contain abamectin (avermectins B1a and B1b), a highly active macrocyclic lactone that has never been used before on cattle in the USA. The patent-pending formulation contains a high loading of piperonyl butoxide which synergizes the abamectin for maximum pesticidal action. XP 820 is particularly effective against horn flies, including strains resistant to synthetic pyrethroid and organophosphate insecticides. XP 820 is also effective against ear ticks, American Dog Ticks, Cattle Fever Ticks (Boophilus species) and Lone Star Ticks. The XP 820 tag has a netweight of 9 grams and a metallic gold color.