Christophe Courteau / Male BurchellÕs zebra (Equus quagga burchellii) pulling the head of a dead pregnant female that died due to complications whilst giving birth, trying to wake her up, Etosha National Park, Namibia. Par...

Carol Walker / Two wild pinto Mustang stallions battle for dominance in Sand Wash Basin, Colorado, USA.

Carol Walker / Head portrait of grey Arabian stallion running in desert dunes near Dubai, United Arab Emirates.

Carol Walker / Two wild Mustang stallions fighting in the White Mountain Herd Area, Wyoming, USA. August.

Richard Du Toit / Burchell's Zebra (Equus burchellii) parents tending to foal, Rietvlei Nature Reserve, South Africa

Kristel Richard / Two cowboys mounted on a Pantaneiro stallion, round up a band of wild Pantaneiro horses, Pantanal, Mato Grosso do Sul, Brazil. August 2015.

Kristel Richard / Two wild Przewalski / Takhi Horse (Equus ferus przewalskii) stallions play fighting Hustai National Park, Tuv Province, Mongolia. Endangered species. September.

Kristel Richard / Przewalski / Takhi Horse (Equus ferus przewalskii) breeding stallion stands alert, Hustai National Park, Tuv Province, Mongolia. Endangered species. September.

Richard Du Toit / Burchell's Zebra (Equus burchellii) stallions fighting, Rietvlei Nature Reserve, South Africa

Richard Du Toit / Burchell's Zebra (Equus burchellii) stallions fighting, Rietvlei Nature Reserve, South Africa

Yva Momatiuk & John Eastcott / Wild Horse (Equus caballus) stallions play fighting, Pryor Mountain Wild Horse Range, Montana

Donald M. Jones / Wild Horse (Equus caballus) fighting stallions, Wyoming