basic introduction:
Mammals are herbivorous livestock of the order Oddhoofed equine. Horses were the main driving force for agricultural production, transportation and military activities in ancient times. With the invention and wide application of power machinery, the value of horses has dropped significantly in some industrialized countries, and almost all field operations have been replaced by tractors. Horses are mainly used for equestrian sports and milk production, and the amount of feeding is greatly reduced. However, in some developing countries and regions, horses are still mainly used for service and are an important source of service.

Origin and domestication Equus originated in the early Tertiary period of the Cenozoic 60 million years ago, and its most primitive ancestor was the protohoof, short in stature, with 5 toes on all four limbs, and a more developed middle toe. The Eocene horse, or ancestral horse, which lived in the early Eocene of the Tertiary Period 58 million years ago, was about 40 centimeters tall. The forelimbs are low and have 4 toes; the hind legs are high and have 3 toes. Simple teeth, suitable for tropical forest life. After entering the Miocene, the dry grassland replaced the wet shrub forest, and the function and structure of the horses changed significantly: the body increased, the limbs became longer, and became a single toe; the teeth became hard and complex. After the evolution of the gradual new horse, the Zhongxin horse and the Shangxin horse, it was not until the Pleistocene of the fourth century that it appeared as a single-hoofed horse with a raised head and a tall body.

Domestic horses are domesticated from wild horses. China is one of the earliest countries to domesticate horses. From the remains of the Dawenkou Culture Period and Yangshao Culture Period in Shandong and Jiangsu in the lower reaches of the Yellow River, it is proved that several wild horse varieties have been domesticated around 6000 years ago. for livestock. Horses were domesticated later than dogs and cattle.

Biological characteristics:
Horses of different breeds vary greatly in size. Heavy breeds weigh up to 1,200 kg and are 200 cm tall; small breeds weigh less than 200 kg and are only 95 cm tall, and so-called pocket ponies are only 60 cm tall. The head is straight and long, and the ears are short. The limbs are long, the bones are solid, the tendons and ligaments are well developed, and the cicadas (commonly known as night eyes) with palm-occipital relics have hard hooves and can run quickly on hard ground. The coat color is complex, mostly liu, chestnut, green and black; the coat is shed once in spring and autumn. The sweat glands are well developed, which is conducive to regulating body temperature, and is not afraid of severe cold and heat, so it is easy to adapt to the new environment. The chest is deep and wide, and the heart and lungs are developed, suitable for running and intense labor. The esophagus is narrow, the monostomach, the large intestine, and especially the cecum are abnormally developed, which is helpful for the digestion and absorption of roughage. No gallbladder, bile ducts developed. The chewing force of the teeth is strong, and the space between the incisors and the molars is called the receiving part. Age was determined by the number, shape and degree of wear of the teeth (Fig. 3), and the senses of hearing and smell were acute. The distance between the two eyes is large, and the overlapping part of the visual field is only 30%, so the judgment of distance is poor; at the same time, the focal length adjustment of the eyes is weak, and it can only form a blurred image for objects beyond 500 meters, but it can be very good for close-range objects. Identify its shape and color. The head and neck are flexible, and the visual surface of both eyes can reach 330°~360°. The outer layer of the retina of the fundus has a layer of photomembrane, which has strong light sensitivity and can see surrounding objects at night. Horses are easy to train. Through the sense organs such as hearing, smell and sight, strong memories can be formed. The average life expectancy is 30 to 35 years old, and the longest can be more than 60 years old. The age of service is 3 to 15 years old, and some can reach 20 years old.