Main Spring, a Canadian-bred gelding owned by the late William D. "Billy" Haggard, III, was the second outstanding mount Haggard loaned to the United States Equestrian Team during the 1960s and '70s following the retirement of Bold Minstrel. Purchased by Haggard after a sensational National Horse Show debut in 1971 under Rodney Jenkins, Main Spring went on to chalk up many international victories under the piloting of Show Jumping Hall of Famers William Steinkraus and Frank Chapot.

Perhaps his most memorable career highlight came in Munich in 1972 in his role as backup to the 1968 Gold Medalist, Snowbound. When the latter sustained a leg injury in the individual competition of the Games, Steinkraus went on to compete Main Spring in the team event and turned in the best overall score of the day in the Nations' Cup, producing one of only three clear rounds in the entire event. The duo helped the U.S. team win the Silver Medal, finishing a mere .25 faults behind the Gold Medal-winning Federal Republic of Germany.

Following the Olympics, Steinkraus and Main Spring went on to help the United States clinch three Nations' Cup wins on the fall circuit at the end of 1972, when they came away with victories at Harrisburg, New York, and Toronto. The year also included wins in the Gubelin Preis at Lucerne and the Munchner Versicherung at Aachen as well as the Grand Prix of Toronto. Steinkraus also rode Main Spring to two victories at the National Horse Show in Madison Square Garden, winning the Volco Trophy and the Stake, and also to the International Individual Championship in Harrisburg.

After Steinkraus retired at the end of 1972, Main Spring acquired a new partner in Steinkraus's teammate Frank Chapot. Main Spring and Chapot aided the U.S. team to two Nations' Cup victories that year - one in Washington and one in Toronto. They also emerged victorious in the Grand Prix of Toronto. Nationally, Chapot and Main Spring won the Volco Trophy at the National Horse Show as well as the Bonus Class in Washington.

The highlight of Main Spring's partnership with Chapot came in 1974 when the pair earned the individual Bronze Medal at the Show Jumping World Championships in Hickstead, England. That same year, they won the prestigious King George V Gold Cup in London and helped the United States clinch victory in the Nations' Cup competition in New York. For the second year in a row, Chapot rode Main Spring to the win in the Grand Prix of Toronto. Following Steinkraus's previous win with the horse there in 1972, this win marked the third consecutive year that Main Spring had earned the title in that prestigious Grand Prix, serving as a fitting finish to a successful career.