48 May/June 2013 • equine HealtH © 2 01 3 M A H ea lth ca re L td A ccording to fossil records, the ancestor of the modern-day horse is thought to have appeared on Earth around 65 million years ago. At this time, the ‘dawn’ horse, known as Hyracotherium, was about the size of a Labrador, and spent it’s time amongst the undergrowth of the tropical forests in which it first lived. The horse as a species is relatively young in evolutionary terms. To put their development into perspective, it is believed that the Earth is some 4600 million years old, and that human ancestors first evolved around 40 million years ago. The dog-like Hyracotherium lived on a diet that is very different to that of the modern-day Equus Caballus. Although still herbivorous creatures, the dawn horse survived on a diet of young shoots, lush, green leaves and berries, which were easily found within the rainforest undergrowth. Indeed, a fossilised specimen of Hyracotherium from this early evolutionary period was found complete with fossilised stomach contents of grape pips! These animals were classed as browsers; they selected high-quality foodstuffs that were typically high in sugar. This is in comparison to the domestic horse, which is a grazing animal, spending little time browsing, and consuming larger amounts of fibrous forages over 18 to 20 hours in any 24-hour period. The browsing nature of Hyracotherium meant that the dentition of this early ancestor was very different to that of the modern horse. The teeth were typically unspecialised molars that were low-crowned, indicative of animals not reliant on a diet high in fibre. Although little is reported about the gut of the dawn horse, it has been found from detailed analysis of the fossil record that they had a considerably smaller hind gut compared with horses and ponies today. As the dawn horse spent much of its time in the brush of the forest, Hyracotherium, or Eohippus as it is also called, relied on hiding in vegetation cover to evade capture by predators. The habitat of Eohippus dictated much of the physical characteristics typical of the species at that point in time. For instance, Hyracotherium had eyes placed very much on the front of the head, much like those seen on a dog or cat, rather than on the side of the head as is typical of horses now. This is probably because spending most of its Catherine Hale CBiol MSB, Global Equine Specialist LFA Celtic and Dr Andrew Hemmings, Senior Lecturer, Royal Agricultural University investigate the development of the equine gut A natural diet