Ruminant mammals use their horns for both defense from predators and intraspecific combat. Convergent evolution of horn materials and structures has been inferred in the families Bovidae and Antilocapridae. To investigate the composition and microstructure of horn sheaths, four representative species were examined (bighorn sheep, domestic sheep, mountain goat, and pronghorn antelope). Bighorn sheep and domestic sheep are from the same genus but have different impact fighting energy. The mountain goat, from the same family as the sheep (Bovidae), presents much lower impact fighting behavior. Pronghorn antelope, from a different family (Antilocapridae) also does not employ high impact ramming in intraspecific fights in contrast to the two sheep. Optical microscopy images show that the horns of all four species consist of keratin sheath formed by lamellar keratinized cells but differ in tubule densities and porosities. Mechanical tests results in the dry and hydrated conditions will be presented. This work is supported by a Multi-University Research Initiative through the Air Force Office of Scientific Research (AFOSR-FA9550-15-1-0009).