Publicly traded real estate investment trusts that buy MBS continued to whittle down their positions in government and agency product during the third quarter, a trend that some fear may have no bottom. Market leader Annaly Capital Management trimmed its MBS holdings to $66.3 billion during the period, a 1.9 percent sequential decline, but an ugly 18.6 percent drop compared to the third quarter of last year. It is investing more of its cash in commercial product. Number two ranked American Capital Agency Corp. was...[Includes one data table]