Longevity of English Thoroughbred Horses 43 



actually reached by thoroughbred mares is largely determined 

 by human intervention, since many which disappeared from 

 the record at ages of 25 or over were probably capable of living 

 longer — some no doubt did so, dying unrecorded. The stallion 

 Matchem (1749-1781) reached a reputed age of 33; in the 

 obituary lists of the Stud Book one other stallion reached 32, 

 and four reached 31. 



These ages agree with maximum authenticated records in 

 other breeds (Hokkaido ponies 32 -f, Matsumoto, 1935; 

 Hafling mares, over 32, Schotterer, 1939; Lipitsa horses 

 (J31, 533, Kadic, 1949). Claims of higher ages have been 

 reviewed elsewhere (Comfort, 1956). Many of these refer to 

 ponies, and none is supported by Stud Book records. Thirty- 

 eight years is recorded in a captive zebra (Weber, 1942). 



Effects of parental age on the longevity of progeny 



Vitt (1949) has claimed that the longevity and racing per- 

 formance of thoroughbred horses are substantially influenced 

 by the age of both dam and sire, and that impairment of 

 vigour by the use of old breeding stock is cumulative. He 

 found that in a sample of 100 mares from the early years of 

 the General Stud Book, the progeny of dams twelve years old 

 or less developed more slowly, judged by the age at first 

 foaling, and lived longer {6^=4^ =19-5 years) than the progeny 

 of dams aged 13 or more {e^^4^ = 16-4 years). Absolute 

 figures and standard errors are not given, and it is not clear 

 whether the estimates are corrected for losses or based on the 

 distribution of recorded deaths alone. Vitt also compared the 

 fertility and racing form of foals by old and young stallions, 

 and concluded that there was an equally marked paternal age 

 effect, the optimal performance being reached by the foals of 

 stallions 8-16 years old out of mares 6-13 years old. 



To test this the lives in sample A were distributed (a) by age 

 of dam at foaling, (b) by age of sire at covering, one year 

 earlier, (c) by age of dam at foaling and sire at covering, where 



