CATTLYST® Type A Medicated Article Rethink ionophores: Think CATTLYST for weight gain in feedlot cattle. Ionophores are proven to improve cattle feed efficiency. But what if weight gain is just as important for your feedlot — and your profits? Then think about CATTLYST®. Unlike Rumensin®, CATTLYST: Is labeled for boosting weight gain in confined feedlot cattle. Requires no step-up program, eliminating the need for multiple starter rations. Is approved for use with AUREOMYCIN®. When CATTLYST is fed in combination with AUREOMYCIN, a veterinary feed directive is required.