http://www.deutsche-finanzagentur.de/fileadmin/Material_Deutsche_Finanzagentur/PDF/Aktuelle_Informat ionen/Auktionsergebnisse_E.pdf

The last auction of 10 year bunds was October 19th and 925 million out of 5,000 million € was retained. The first auction in 2011 was January fifth and 1084 million out of 5 billion was retained. So apart from this last auction there was no movement in the retained share.

And here is an explanation of  seconderay markets finance activity.

http://www.deutsche-finanzagentur.de/en/institutional/secondary-market/secondary-market-activities-f inance-agency/  

"The volume of securities retained for market operations varies widely from auction to auction. Since 2005, the amount retained has averaged about 20% of the issuance volume (which also included money market paper and inflation-linked German Government securities)."