Alex Mustard / Two female Common seahorses (Hippocampus kuda) fighting over territory on the seabed. The brief fight was preceeded by a ritualised, synchronised parade. Bitung, North Sulawesi, Indonesia. Lembeh Stra...

Alex Mustard / Common seahorse (Hippocampus kuda) female wrapping her prehensile tail around piece of wood on the seabed. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Ben Gillett / Slow motion clip of a female Appaloosa horse grooming a male, Bristol, England, UK, May.

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) mother and foal, Oshoto, Wyoming

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) mother and foal, Oshoto, Wyoming

Carol Walker / Wild pinto Mustang mare and foal running in Sand Wash Basin, Colorado, USA.

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

Richard Du Toit / Burchell's Zebra (Equus burchellii) mother and foal, Rietvlei Nature Reserve, South Africa

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

Suzi Eszterhas / Domestic Horse (Equus caballus) mother and foal running, Sonoma County, California

Sean Crane / Zebra (Equus quagga) mother and foal near rainbow, Ol Pejeta Conservancy, Laikipia, Kenya

Richard Du Toit / Burchell's Zebra (Equus burchellii) mother and foal in tall grass, Rietvlei Nature Reserve, South Africa

Kristel Richard / Eagle hunter mounted on Mongolian horse with his female Golden eagle (Aquila chrysaetos) at Eagle Hunters Festival, near Sagsai, Bayan-Ulgii Aymag, Mongolia. September 2014..

Richard Du Toit / Burchell's Zebra (Equus burchellii) mother nuzzling foal, Rietvlei Nature Reserve, South Africa

Jeff Vanuga / Guardian riding Camargue horse through water at sunrise, Camargue, Bouches du Rhone, France, May 2013.

Kristel Richard / Portrait of a rare five-day old Posavina filly hidden by her mother's tail, Lonja, Croatia, August.

Kristel Richard / An Einsiedler / Swiss warmblood mare (Equus caballus) cantering, Schwyz, Switzerland, July.

Kristel Richard / A group of Pure Arab, Shagya Arab and East Bulgarian fillies running in snow, Kabiuk National Stud, Shumen, Bulgaria.

Kristel Richard / A group of Pure Arab, Shagya Arab and East Bulgarian fillies running in snow, Kabiuk National Stud, Shumen, Bulgaria.

Michel Poinsignon,Michel Poinsignon / Merens horse (Equus caballus) mare with resting foal, Pyrenees mountains, France, August.

Kristel Richard / Wild / feral Dulmen ponies (Equus caballus) close up of herd of mares and foals running on the Duke of Croy's estate, Meerfelder Bruch, North Rhine-Westphalia, Germany, May 2011

Carol Walker / Wild horse / mustang, mare rolling, Pryor Mountains, Montana, USA, July

Carol Walker / Andalusian mare running in snow storm, Colorado, USA

Kristel Richard / Silhouette of two traditionally dressed Indian riders, mounted on Kathiawari mares, backlit at sunset, in Gujarat, India, January 2011, Model released

Richard Du Toit / Burchell's Zebra (Equus burchellii) mother and foal, Kwazulu Natal, South Africa

Kristel Richard / A Kathiawari mare (Equus caballus) standing in Junagadh National Stud, Gujarat, India.

Kristel Richard / Close up of the curved ears of a rare Cremello Kathiawari mare with young Indian boy riding her, in Jasdan, Gujarat, India. The pink points on her head are tradionally put by women during ceremonies,...

Carol Walker / Mustangs / Wild horses, stallion and mare trotting, Return to Freedom Sanctuary, Lompoc, California, USA

Mitsuaki Iwago / African Lion (Panthera leo) female attacking Burchell's Zebra (Equus burchellii), Serengeti National Park, Tanzania

Richard Du Toit / Burchell's Zebra (Equus burchellii) mother and foal, summer, Savuti, Chobe National Park, Botswana

Pete Oxford / Burchell's Zebra (Equus burchellii) foal nuzzles mother in waterhole, Africa

Pete Oxford / Burchell's Zebra (Equus burchellii) foal standing beside mother in waterhole, Africa

Mitsuaki Iwago / African Lion (Panthera leo) female chasing Burchell's Zebra (Equus burchellii), Serengeti, Tanzania

Mitsuaki Iwago / African Lion (Panthera leo) females feeding on Burchell's Zebra (Equus burchellii), Serengeti National Park, Tanzania

Mitsuaki Iwago / African Lion (Panthera leo) female chasing Burchell's Zebra (Equus burchellii), Serengeti National Park, Tanzania

Mitsuaki Iwago / African Lion (Panthera leo) females killing Burchell's Zebra (Equus burchellii), Serengeti National Park, Tanzania

Mitsuaki Iwago / Burchell's Zebra (Equus burchellii) mother and foal, Botswana

Mitsuaki Iwago / Burchell's Zebra (Equus burchellii) mother and foal, Botswana

Jim Brandenburg / Burchell's Zebra (Equus burchellii) mother and baby nuzzling, Namibia

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) mare and her foal flee danger in cloud of dust in the summer season, Wyoming

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) palomino yearling filly and her spring foal brother grooming each other, Pryor Mountain Wild Horse Range, Montana

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) mare and foal silhouetted against evening sky during summer, Montana

Pete Oxford / Two Chagra cowboys on an overnight ride at a hacienda to herd cattle, Andes Mountains, Ecuador

Mitsuaki Iwago / Domestic Horse (Equus caballus) and foal, Australia

Juan Manuel Borrero / Mule - offspring of male donkey and female horse - Spain

Alex Mustard / Yellow longsnout seahorse (Hippocampus reidi) female holds onto a sea rod with its prehensile tail, on a coral reef. West Bay, Grand Cayman, Cayman Islands, British West Indies. Caribbean Sea.

Alex Mustard / Common seahorse (Hippocampus kuda) female gripping onto a piece of waterlogged wood with her prehensile tail. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Oliver Wright / Hairy legged horsefly (Hybomitra bimaculata) female, portrait. Skipwith Common National Nature Reserve, North Yorkshire, England, UK. May. Focus stacked image.

Tony Heald / Arabian horse, female and foal trotting one behind the other. Namibia.

Juan Carlos Munoz / Sorraia horses, adult and two foals standing in meadow. Middle Coa, Coa Valley, Western Iberia, Portugal. April 2016.

Juan Carlos Munoz / Sorraia horses, mare and foal standing amongst wildflowers in meadow. Middle Coa, Coa Valley, Western Iberia, Portugal. April.

Ben Gillett / Close up of head/eye, female Appaloosa horse. Domesticated. Bristol, UK

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii) mare. Reintroduced through European Endangered Species Program into acclimatisation enclosure, awaiting release into wild. Takhin Tal National Park, Great Go...

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii), four mares grazing in steppe with mountains beyond. Reintroduced through European Endangered Species Program into acclimatisation enclosure, awaiting releas...

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii), group including female and foal, walking. Great Gobi B Strictly Protected Area, Mongolia. August.

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii), three including female and foal silhouetted at sunset. Great Gobi B Strictly Protected Area, Mongolia. August.

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii) mare grazing. Reintroduced through European Endangered Species Program into acclimatisation enclosure, awaiting release into wild. Takhin Tal National Park,...

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii), two mares nuzzling. Reintroduced through European Endangered Species Program into acclimatisation enclosure, awaiting release into wild. Takhin Tal National...

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii) mare grazing. Reintroduced through European Endangered Species Program into acclimatisation enclosure, awaiting release into wild. Takhin Tal National Park,...

Cyril Ruoso / Przewalski horse (Equus ferus przewalskii) female and foal walking through steppe in morning light. Great Gobi B Strictly Protected Area, Mongolia. August.

Cyril Ruoso / Przewalski's Horse (Equus ferus przewalskii) mother and three week old foal, Gobi Desert, Mongolia

Cyril Ruoso / Przewalski's Horse (Equus ferus przewalskii) mare grazing, Gobi Desert, Mongolia

Kristel Richard / UVM Morgan horse filly cantering, at the historical stud University of Vermont Morgan Horse Farm, Weybridge, Vermont, USA

Kristel Richard / UVM Morgan horse filly cantering, at the historical stud University of Vermont Morgan Horse Farm, Weybridge, Vermont, USA

Kristel Richard / UVM Morgan horse filly standing alert, at the historical stud University of Vermont Morgan Horse Farm, Weybridge, Vermont, USA

Kristel Richard / UVM Morgan horse filly cantering, at the historical stud University of Vermont Morgan Horse Farm, Weybridge, Vermont, USA

Kristel Richard / UVM Morgan horse filly cantering, at the historical stud University of Vermont Morgan Horse Farm, Weybridge, Vermont, USA

Kristel Richard / A young wild black filly (Equus caballus) standing alert in the Cincar mountains, near Livno, Bosnia and Herzegovina.

Philippe Clement / Black Shetland pony mare nursing foal in grassland along the coast on the Shetland Islands, Scotland, UK

Hiroya Minakuchi / Wild Horse (Equus caballus) mother and foal, Cape Toi, Miyazaki, Japan

Kristel Richard / Rare semi-wild Hmong horse, filly, standing alert among mares in a dry rice field, Xieng Khuang, Laos.

Kristel Richard / Rare semi-wild Hmong horse, filly, standing alert among mares in a dry rice field, Xieng Khuang, Laos.

Kristel Richard / Portrait of a wild rare Eriskay horse, mare, on Holy Isle, Scotland, UK. Critical status by Rare Breeds Survival Trust.

Sebastian Kennerknecht / Burchell's Zebra (Equus burchellii) females nuzzling, Kruger National Park, South Africa

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) mother grazing with foal, Oshoto, Wyoming

Yva Momatiuk & John Eastcott / Mustang (Equus caballus) mother and foal, Oshoto, Wyoming

Yva Momatiuk & John Eastcott / Icelandic Horse (Equus caballus) mare and foal, Iceland

Yva Momatiuk & John Eastcott / Icelandic Horse (Equus caballus) mare and foal, Iceland

Alex Mustard / Yellow seahorse (Hippocampus kuda) female moves across a pebbly seabed in shallow water. Ambon Bay, Ambon, Maluku Archipelago, Indonesia. Banda Sea, tropical west Pacific Ocean.

Cyril Ruoso / Feral Horses (Equus caballus) mating, Namib-Naukluft National Park, Namibia.

Cyril Ruoso / Feral Horse (Equus caballus) pair mating with another standing nearby, Namib-Naukluft NP, Namibia.

Cyril Ruoso / Feral Horse (Equus caballus) mare kicking out at stallion with foal nearby, Namib-Naukluft NP, Namibia.

Cyril Ruoso / Feral Horse (Equus caballus) mother and foal, a few days old, Namib-Naukluft National Park, Namibia

Kristel Richard / Two Paso Fino mares (Equus ferus caballus) galloping in a field, Rionegro, Antioquia, Colombia. August.

Kristel Richard / Four Paso Fino mares (Equus ferus caballus) galloping in a field, Rionegro, Antioquia, Colombia. August.

Kristel Richard / Man riding a Trocha mare in trot, Rionegro, Antioquia, Colombia.

Bruno D'Amicis / Domestic cow looking at Apennine / Italian wolf (Canis lupus italicus) adult male feeding on horse carcass. Abruzzo, Central Apennines, Italy. November.

Anup Shah / Burchell's Zebra (Equus burchellii) mother nuzzling foal, Masai Mara, Kenya

Anup Shah / Burchell's Zebra (Equus burchellii) foal following mother, Masai Mara, Kenya

Anup Shah / Burchell's Zebra (Equus burchellii) mother and foal, Masai Mara, Kenya

Anup Shah / Burchell's Zebra (Equus burchellii) mother and running foal, Masai Mara, Kenya

Daniel Heuclin / Navajo horse mare and foal, Arizona, USA, May.

Daniel Heuclin / Navajo horse mare and foal, Arizona, USA, May.

Daniel Heuclin / Navajo horse mare and foal, Arizona, USA, May.

Ernie Janes / Haflinger horse mare and foal in meadow, Norfolk, England, UK, March.

Ernie Janes / Haflinger horse mare and foal running in meadow. England, UK