I'm not an expert but the extinct ancestor of the modern cow, the Auroch was quite a large mammal and at least according to wikipedia [citing van Vuure, T. (Ci

I'm not an expert but the extinct ancestor of the modern cow, the Auroch was quite a large mammal and at least according to wikipedia [citing van Vuure, T. (Cis) (2005). Retracing the Aurochs – History, Morphology and Ecology of an extinct wild Ox. Sofia-Moscow: Pensoft Publishers. ISBN 954-642-235-5] claims that the main predators were big cats (lions and tigers) and hyenas). Across much of the cows modern range those predators don't exist. Possibly a wolf, Siberian tiger or large brown bear would predate a cow, similiar to the predators of a moose but it doesn't seem like they are under constant fear of predators any more. Cows are often left to pasture across vast unfenced area of basically wilderness and don't seem particularly afraid nor at risk of predation (otherwise they'd need to be guarded).