Sex ratio of offspring in domestic animals Race horses in Japan
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概要
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The data used in the present study were collected from the records in the Thoroughbred Year-lings Catalogue of Japan (from 1970 to 1973) which was published by the Japan Light-Breed HorseAssociation. The catalogue contained three breeds of horses, i.e., Thoroughbred, Non-Thoroughbred, and Thoroughbred Strain, and data collected from eight districts (see the remarks of Table 1). Thetotal number of offspring and of sires listed in the catalogues were 20, 662 and 493, respectively. The results obtained from a study on the secondary sex ratio of race horses in Japan are summarized as follows.<BR>1. Total sex ratio was 49.3 ( ?? %). Its shift was significant at a 5% level. With regard to eachdistrict and each breed, a shift of sex ratio to female was seen only in the Thoroughbred breed in the C district. There was no significant shift of sex ratio in the total of the eight districts for any breed, or in the sum total of the three breeds for any district (Table 1).<BR>2. A regional difference in sex ratio was observed most frequently between the H and any other district. It was difficult, however, to find a general rule for regional differences from the present study. Therefore, it cannot be concluded that there is a regional difference in the sex ratio of race horses (Table 2).<BR>3. A large number of sires showed a shift of sex ratio to female than a shift to male (Table 3).<BR>4. Shifts of sex ratio were found in the Thoroughbred breed in February and March, in the Non-Thoroughbred breed in March, in the Thorughbred Strain in February, and in all the three breeds in February and March. It cannot be concluded, however, that there is a relationship between season and sex ratio (Table 4).<BR>5. Shifts of sex ratio were noted in sires at six years of age (to male), and at twelve and eigh-teen years of age (to female). When the sires were divided into three age groups, a significant dif-ference in sex ratio was found only between the two older groups. No permanent shift of sex ratio with the advance in age of sire, however, could be noted in the present study (Table 5 and 6).
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