Non-agency mortgage securities production dominated the first quarter MBS market in terms of total volume, accounting for a record 55.0 percent of total issuance during the period. The non-agency sector first broke the 50 percent mark during the third quarter of 2004 and it hasn’t looked back yet. The non-agency MBS market share more than doubled from 2003, when it was 21.6 percent, to last year, when it accounted for 45.9 percent of issuance for…