36 A. Comfort 



of thoroughbreds. Another was to see whether the records 

 could be used to determine the extent of the parent-offspring 

 and sib-sib correlations for lifespans. 



The following account combines and summarizes the results 

 already described elsewhere (Comfort, 1958a, b, 1959a). 



Materials and Method 



The Stud Book consists to date of 34 volumes, published at 

 four-yearly intervals since 1808. It is essentially a nominal 

 list of brood mares, giving details of the serving, foaling and 

 ownership of each since the last entry. Arabian mares are 

 listed separately. 



From this record can be obtained (1) the year of birth of 

 every thoroughbred foal under the name of its dam, (2) the 

 life history of every filly which returns to stud as a brood 

 mare, from her first covering by a thoroughbred stallion until 

 death or disposal from the stud. 



The life histories were extracted by following each in- 

 dividual animal by name from its first appearance as a brood 

 mare until its last ; in all, including those required to establish 

 parental longevity, and additional lives scored in the course of 

 coat-colour studies, about 10,000 histories were extracted in 

 this way. Initial samples taken were ( 1 ) all the thoroughbred 

 fillies foaled in Britain, excluding Ireland, in the years 1875-80 

 (Sample A) and 1860-64 (Sample B) which subsequently re- 

 enter the record as brood mares, (2) all the Arabian mares 

 foaled in 1880 and the 35 subsequent years — a compact group 

 of manageable size, where over half the fillies returned to 

 stud. The original six annual cohorts of thoroughbreds 

 (Sample A) were chosen so that their survival period avoided 

 the World Wars. After this sample had been analysed. Sample 

 B was taken to obtain more data upon the relationship of 

 longevity to parental age. The thoroughbred cohorts of 1900 

 and 1901 were scored later, to see whether secular changes had 

 occurred in the course of the record. 



