Sources of stamina among North American stallions seems to be getting leaner as judged by the recent release of the Grayson-Jockey Club Research Foundation's annual report of sire durability and soundness.
Among the leading 30 stallions by starts per starter, 13 sires have died, two are pensioned, and three have been relocated to either Argentina or Australia.
The stallions included in the durability study are the top 200 sires by progeny earnings for the 2016 calendar year in order to assure relevance to the commercial breeding and sales market. The study's key statistics of starts per starter and percentage of starters from foals of racing age, however, are all lifetime statistics.
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