In the European market for long-term bonds, a once-loyal and deep pocketed customer is about to start shopping elsewhere.

The €1.6 trillion ($1.9 trillion) Dutch pension system — the largest in the region — is undergoing a major transformation aimed at making it more sustainable for an aging population. Funds will invest more in riskier assets and less in bonds, with a big drop in demand expected for long-term interest-rate hedges.