When Roy and Gretchen Jackson purchased their 190-acre property in Chester County, Pennsylvania, in 1978, they christened it Lael Farm, the Gaelic word for loyalty. Today, more than 40 years into the couples' transatlantic forays in the world of breeding and racing Thoroughbreds, that name could hardly be more appropriate. The Jacksons, both lifelong horse people, became household names in the sport and beyond in 2006 during their months-long attempt to save the life of their GI Kentucky Derby winner Barbaro (Dynaformer) after the colt suffered what was ultimately a...