Most anthelmintics are safe for use throughout pregnancy, but precautions and contraindications on package inserts should be heeded. In general, anthelmintics should not be administered to mares during the first 60 days of gestation (organogenesis). Parasite control programs should be tailored to meet the particular farm needs. Also see Gastrointestinal Parasites of Horses. Pregnant mares should be administered ivermectin or a benzimidazole 1–3 days before foaling to prevent lactogenic transmission of Strongyloides westeri, which can cause diarrhea in young foals.