Is it permissible to distribute the value of a head of livestock to the poor instead of slaughtering it, after vowing to slaughter a head of livestock every year?

A vow must be fulfilled if it is an act of obedience, for Allah has praised those who fulfill their vows. Allah Almighty says: "They fulfill [their] vows and fear a Day whose evil will be widespread." And the Prophet, peace and blessings be upon him, said: "Whoever vows to obey Allah, let him obey Him." The questioner's vow is of the nature of acts of devotion through which one draws closer to Allah, like sacrifices. Therefore, it must be fulfilled in the manner he committed to, and it is better than donating its price because he vowed to slaughter, and it is the shedding of blood in the way of Allah. A vow conditioned on a contingency must be fulfilled.