If one man owns a single sheep while another owns thirty-nine, or if forty men possess forty sheep—one sheep each—and they merge their flocks for a full lunar year with all the conditions we have mentioned in place, only one sheep is due in zakat on the whole, in proportion to their respective ownership. Thus, in the first example the owner of the lone sheep is responsible for one-fortieth of a sheep, while the owner of the thirty-nine owes the remainder. In the second example each of the forty men owes one-fortieth of a sheep. Likewise, if three men have one hundred and twenty sheep, forty apiece, they must jointly pay a single sheep, divided into thirds among them.

Just as commingling has the effect you have seen, separation also has consequences according to Imam Ahmad. If a man’s freely-grazing livestock are dispersed such that each group is separated from the other by more than the distance at which the prayer may be shortened, each group is treated independently: should one group reach the legal threshold, zakat is due on it; if it falls short, nothing is owed on that group, and no portion is added to, or combined with, any other. This is the view of Imam Ahmad.

The majority of scholars, however, hold that dispersal does not affect the property of a single owner; every portion is combined with the rest for legal purposes even if scattered. This is the stronger opinion. Allah knows best.