The D-book is a subsidiary registry, or sub-category within the KFPS studbook. Like the B-books, the D-book was created for horses whose breeding or lineage does not conform with KFPS policies, but are still purebred Friesians. A more recent creation than the B-books, the D-book was created to comply with European Union regulations concerning the recognition of breed registries. In short since only one European KFPS affiliate executes its own registration and breeding program independently of the KFPS, the D-book deals specifically with the offspring of horses registered with the German studbook FPZV.Horses are eligible for the D-book if the dam is registered in either the KFPS main studbook or the KFPS D-book, and the sire has completed and passed all the current requirements for the FPZV Stallion Book I.
Horses are not eligible for the D-book if:

• the dam is in the KFPS B-Book
• the sire is a stallion who has only partially met the approval requirements with the current FPZV testing
• the sire is a stallion within the FPZV which was previously approved by the KFPS then disapproved on offspring (ex: Adel 357, Jelke 367, etc). Horses sired by disapproved KFPS stallions do not qualify for the D-book on the grounds that the KFPS has previously found undesirable qualities in their offspring.

Offspring with a sire as described above are eligible for KFPS B-book II.