After Hirotaka subdivided the domain by giving a fief of 5,000 koku in rice to his brother, Shigetsune YAMAGUCHI, the total Kokudaka (yield of rice) of the Ushiku Domain equaled 10,000 koku in rice.
弘隆は弟・山口重恒に5000石を分知したため、牛久藩の総石高は1万石となる。