Morphological Studies on the Chestnut of the Horse

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On the origin, physiological function, and some other things of the chestnutof the horse, there are no reliable theories at all. Some researchers have away of thinking that the chestnut is apt to be influenced by the general healthcondition of the climate and other conditions of nature, since it is composedof the same tissue as the hoof and skin which are originated from the ectoderm.Others presume that the chestnut may remain unchanged in character throughoutlife, as well as human finger print does, although, there is no reasonableexplanation on the development of the chestnut. The present studies were carried out to clarify the morphology of thechestnut. In them, samples were collected from 139 adult horses, which consistedof 95 of the Light breed, 39 of the Half breed, and 5 Japanese nativehorses. For detailed observation, photographs were taken by a camera accompaniedby the Micro Extension Tube and the Universal Ringflash. At thetime of enlargement, the actual size of the chestnut was printed on a negativefilm. On the other hand, the body weight and height of each horse weremeasured by the regular scales exclusively used for horses. Relationships ofthe character of the chestnut were investigated to breed, sex, age, color of haircoat, birth place, body height, and others. The following results were obtained. 1) The foreleg chestnut is located at the lowest one-fourth of the antibrachium on the medial side. The hind leg chestnut is located at the upper about two-sevenths of the distance between hock and fetlock on the medial side. Little deviations were found in the position of the chestnut of either leg among the horses used. 2) The length of the foreleg chestnut was the greatest in the Thoroughbred (54.4±9.8 mm), which was followed by the Half breed, Japanese native horses, and the Anglo-Arab in the decreasing order of length . The length of the hind leg chestnut was the greatest in the Half breed (42 .8±14.3 mm), which was followed by the Thoroughbred, Anglo-Arab, and Japanese native horses in the decreasing order of length . 3) There was a significant difference in the surface area between the foreleg chestnut (8.8±2.8 cm2) and the hind-leg chestnut . 4) The surface area of the fore and hind leg chestnut was the greatest in the Half breed (9.6±2.79 and 5.0±2.43 cm<SUP>2</SUP>). There was a significant difference in this area between the Half breed and Japanese native horses (6 .9±1.46 and 3.0±1.87 cm<SUP>2</SUP>), but no differences among the Thoroughbred, Anglo-Arab, and Half breed. 5) There was no constant relationship of the surface area of the chestnut to the sex, age, or color of hair coat. 6) A slight correlationship could be found between the surface area of the chestnut and the body height, weight, girth, or the circumference of the cannon and coronet. 7) When the chestnut was classified morphologically according to the Horse Identification System adopted by the New York Jockey Club, the B type was the most predominant (67.8%) and the C and A types were also predominant in the foreleg. In the hind leg the B type was the most predominant (20.7%) and some other types were also found (A, C, D, E, F, I, M, O, Q, R, S, X and Y types). 8) The chestnut was classified morphologically into 8 types according to the identification system which is used regularly in Japan. It was found that the scallion shape was predominant (55.8%) and the ellipse, gourd, and spindle shapes were seen in the majority of the remainder in the foreleg . These four types were found in about 50 per cent in the hind leg, where the V, rod, round, and irregular shapes were also noticed. 9) When the pattern of the surface of the chestnut was examined, the scaly pattern was the most predominant and the radiant and flat patterns were predominant in the foreleg. The scaly and flat patterns occupied the majority in the hind leg, but the radiant pattern was very rare in the hind lei
日本ウマ科学会の論文

Morphological Studies on the Chestnut of the Horse

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日本ウマ科学会 | 論文

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