This order followed Daijokanpu (the official documents of the Daijokan, the office of the supreme political leader) issued in the previous year, which required umakai liberated together with zakko to work the shift at Meryo (the section taking care of imperial horses) for the number of days equivalent to that of, and in place of, zoyo.
またこれに先立って前年に雑戸とともに解放された馬飼に対して雑徭に替わってそれに相当する日数を馬寮にて交替勤務するようにとした太政官符が出されている。