Yields on Fannie Mae and Freddie Mac mortgage securities that guide US home-loan rates reached record lows relative to 10-year Treasuries as investors search for higher returns amid limited refinancing by borrowers. Fannie Mae’s current-coupon 30-year fixed-rate mortgage bonds narrowed 0.02 percentage point to about 0.58 percentage point more than 10-year Treasuries. The gap reached 0.59 percentage point on March 29, two days before the Federal Reserve ended its buying of $1.25trn of so-called agency mortgage bonds. The spread matched that low two weeks ago.