Although a pensioner at Claiborne Farm, where he was born and raised and stood at stud, Boundary is an interesting horse in terms of pedigree and physique because he combines several elements that are important for understanding the mechanics of a racehorse in terms of its pedigree.
On pedigree, many observers might have expected Boundary to have some classic potential, at least over European courses at the mile. And overall, his physique is more classic than typically “sprinter,” with the implication of limitation in distance.
Boundary proved on the racecourse that he was a very good racehorse, although never in the hunt as a classic contender, and as a sire, he contributed a useful amount of power and speed to most matings, as well as adding quality to his offspring.
Boundary was one of many good sons of top sire Danzig, who sired champions and classic winners, racers who showed top class at 2 and beyond, and a variety of horses who found their best form at distances from five furlongs to a mile and a half or beyond. Clearly, a sprint specialist like Boundary was on the shorter end of that spectrum of performance, but like the top European sprinter Dayjur, Boundary was a very fast horse.
Boundary had a high cruising speed because of his advantages of power behind the saddle. He is very strong through the loins, across his gluteal and hamstring muscles in his hindquarters, and in his gaskin. The power from these strong and well-developed muscles allowed the horse to stretch out effectively and use his stride to advantage early. And his stride is a factor from his back and body length. He has an acceptably short back and gets his body length from the depth and angle of his shoulder and hip.
Despite his muscle mass behind, however, Boundary is not gross or coarse. He is a sprinter with the quality of a miler, showing a good expression, top line, and length through the body. He has the balance and muscularity to show immense speed, and on type, he should have run farther than six or seven furlongs effectively.
Perhaps that helps this sire in producing runners who can succeed a bit outside the sprint boundaries. The most famous of these is 2008 Kentucky Derby and Preakness winner Big Brown, who has all the best qualities of Boundary, allied with a dash of finesse that allowed him to stretch out to 10 furlongs successfully.
Prior to Big Brown, the best of the Boundarys were English highweight juvenile Minardi, a G1 winner at 2 who placed in the Irish 2,000 Guineas over a mile at 3; the sprinting G1 winner Pomeroy; and the G1-placed She’s Classy (Hollywood Starlet) and Roxelana (Acorn).
Their natural speed and generally well-balanced body type have made the Boundary stock popular at the sales, with Minardi selling for $1.65 million as a yearling at the Keeneland September auction. Horsemen appreciated the look of his early foals to such a degree that Boundary became quite a talking horse even as an unproven sire.
No doubt a part of the reason for the appealing looks of his offspring is that Boundary matches well with a rather wide spectrum of mares to produce a speedy and athletic-looking foal. Biomechanically, this is what I would expect from Boundary, who fit a wide variety of mares to produce good racing prospects. Although very fast, Boundary was not overburdened with power, and a quick, good-bodied mare from the lines of Mr. Prospector or Northern Dancer was the type that most suited him by reproducing his own best qualities.