Horses, Donkeys, Antilopes and Bovines seem to have an evolutionary advantage in growing masses of hair on top (and sometimes below) the neck. Is that to hinder predators biting?
I am not aware of the evolutionary advantage of the mane in the animals that you mention. In fact, the only reference I could find talks about a predator, not a prey, and thus it might indicate that mane is not mainly an adaptation against predation. I also want to mention that not every trait in every animal is advantageous at the current moment, many traits are 'vestiges' from previous adaptations (or maladaptations). In this case, however, the widespread appearance of the trait in different animal groups might indicate that it is in fact adaptive.
The evolution of mane in the lion seems to be related to sexual selection, as only male lions have mane, but there are competing hypothesis too, in that it appears that the ancestor of the lion was mane-less, and thus the appearance of mane only in lions (and not in other felines) might have been a product of drift (maybe through a bottleneck).
The evolution of mane in other groups of animals might have also been relevant for sexual selection, as it seems that the ancestors of horses had no mane, and thus something that most 'maned' animals have in common is the selective pressure to reproduce and have the mane perhaps as a secondary sexual character indicative of sexual maturation -as it occurs with lions- (I clarify that this is only my own speculation).