Can a single casting of Dispel Magic dispel every creature conjured by a Conjure Animals spell?


Yesterday in a game, my character cast Conjure Animals and summoned 8 wolves†. On the baddies’ turn, one cleric was about to cast Dispel Magic, but the DM changed his mind, deciding that the 8 wolves could not be considered a single magical effect. Personally, I agree with this, but I’m wondering if that stands up to the rules:

Can a single casting of Dispel Magic dispel every conjured creature from one spell at once?


† I’m aware of the debate over who picks the animals; my DM ruled that I could pick.