The world’s biggest buyers of corporate debt are seeking refuge in shorter-maturity bonds as concern deepens that a three-decade rally will end in losses as interest rates rise.

BlackRock Inc. is planning two actively-managed exchange-traded funds focused on short-term debt, with one seeking to have principal repaid within a year, the world’s biggest money manager said in regulatory filings. Loomis Sayles & Co. has favored five- and 10-year corporate notes since April as it’s shifted away from 30-year bonds at its Core Plus Fixed Income team, which oversees about $9.5 billion, said Peter Palfrey, a money manager at the Boston-based firm.