The Ankole-Watusi is a breed of African cattle with enormous horns. Like many other animals with headgear, the horns are used for defense, mating, and to relieve their high body temperature. Blood is pumped into the honeycomb matrix inside their horns, where it is cooled off by wind.
The first photo is by Miloš Anděra.
Three cows (female cattle) in a fight by RLBarn on Flickr. They are only trying to establish dominance, not really hurt each other.
A herd photographed by Charles Hood of Antelope Valley College.
Mama and Calf from Beef Magazine.
Photo by Carol Beckwith and Angela Fisher.
Lurch set the world record for largest steer horns. They are 3 feet in circumference, 7 feet long, and 100 pounds each.
CT Woodie set the record for largest circumfrence of horns in a bull. His horns were uneven and in two out of the three photos I have seen of him, he was standing like that.