ACVPM Toxicology Practice Exam 2026 – Complete Prep Resource

Ionophores act mainly as coccidiostats in poultry and as feed efficiency enhancers in ruminants. In poultry, they inhibit the growth of coccidia parasites in the gut, reducing intestinal damage and improving weight gain. In cattle (and other ruminants), they alter rumen microbial populations to favor more efficient fermentation, which improves feed conversion and growth. They are not used as antibiotics for mastitis, growth hormones for fish, or anthelmintics for sheep, which is why the described use—poultry coccidiostats plus improved feed efficiency in cattle—best captures their primary veterinary role.