Vetrimec Paste (Ivermectin 1.87%) Vetrimec Paste is used to treat parasites in horses. Consults your veterinarian before using. All horses should be included in a regular parasite control program with particular attention being paid to mares, foals and yearlings. Foals should be treated initially at 6 to 8 weeks of age, and routine treatment repeated as appropriate. Consult your veterinarian for a control program to meet your specific needs. Vetrimec Paste effectively controls gastrointestinal nematodes and bots of horses.