A.M. Best has downgraded the financial strength rating to A- from A and the issuer credit rating to "a-"from "a" of Farmers Mutual Hail Insurance Company of Iowa , headquartered in West Des Moines. The rating downgrade reflects FMH's sizeable underwriting losses recorded since 2012, which have led to weak return measures and surplus volatility resulting in a slightly diminished, albeit still strong, level of risk- adjusted capitalization.