how many years did it's career is racing last?
From 1972 to 1973.
Canadian International Stakes
The syndication deal for Secretariat precluded the horse racing past age three. Accordingly, Secretariat's last race was against older horses in the Canadian International Stakes over one and five-eighths miles on the turf at Woodbine Racetrack in Toronto, Ontario, Canada on October 28, 1973. 
how many lengths did secretariat win the belmont stakes 31 lengths. who was "secretariat"? An American Thoroughbred racehorse. who owned this horse? Penny Chenery.
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Secretariat (horse) [SEP] Canadian International Stakes
The syndication deal for Secretariat precluded the horse racing past age three. Accordingly, Secretariat's last race was against older horses in the Canadian International Stakes over one and five-eighths miles on the turf at Woodbine Racetrack in Toronto, Ontario, Canada on October 28, 1973. The race was chosen in part because of long-time ties between E.P. Taylor and the Chenery family, and partly to honor Secretariat's Canadian connections, Laurin and Turcotte. Turcotte missed the race with a five-day suspension: Eddie Maple got the mount. The day of the race was cold, windy and wet, but the Marshall turf course was firm.