by Jay Leimbach, 12/02,2007

Dominant sires and sirelines receive much attention from students of breeding, and desevedly so. But half the names in every pedigree are broodmares, and there is growing evidence that broodmares may contribute slightly more genetically to their offspring than the stallion does. Their X-Chromosomes and mitochondrial DNA may play key roles in both heart function and energy production.

Since nearly half of all fillies will one day reproduce as broodmares, but relatively few males will become sires, broodmares outnumber sires by a large margin. On numbers alone it's very likely that the best genetic influences in history have been female, not male, particularly since broodmares contribute as much or more to the genetic inheritance of the foal.

Although the stallion population is certainly a more select group in general, most of the greatest broodmares in history would never have stood at stud at all had they been males, so it's likely that many of the potentially best sires never even got the chance to breed. Which brings up the important, but often overlooked, concept that the genetic ingredients of a great breeding horse are not the same as the genetic ingredients for a great racehorse.

"Hybrid vigor" is used throughout the agricultural and livestock kingdoms to create great individuals, but these outcrossed hybrids usually make disappointing breeders. The very genetic variety that made them great individuals, later hurts them when they reproduce.

Highly inbred stallions like Galopin (3x3), Isonomy (3x4), Pharos (4x3), Nearco (5x4x4x5), Turn-to (3x3-Pharos), Broad Brush (3x3-Turn-to), and In Reality (3x3) all apparently had the genetic uniformity needed to consistently stamp their offspring with quality. Even Mr. Prospector and Northern Dancer enjoyed a good bit of deeper linebreeding in their pedigrees. With cattle and chickens we also find the best sires are often very highly inbred, although they may not have been impressive individuals themselves. Similarly, many important broodmares have been closely inbred including the dam of Phalaris who was inbred 2x3, etc.

While racing ability certainly plays a part in breeding quality, it's clear from both the greatest sires and the greatest dams that other genetic factors are equally important. Nasrullah, Northern Dancer, and Mr. Propector are rarely, if ever, mentioned among the greatest racehorses, but their male lines now dominate the world. While it is common practice to plan a pedigree with several great stallions, it's much less common to plan a mating loaded with great broodmares--even though such mares may have been the best genetic influences in history.

Duplicating a great broodmare several times in a pedigree, through deep linebreeding a number of generations back, is a good start. Looking back in history we find the most influential broodmare of the 19th Century was probably Pocahontas--whose sons Stockwell, Rataplan, and King Tom were all influential sires that soon spread her bloodlines across the world. The great Man o' War shows a sire, Fair Play, who was 5x5-Pocahontas, and a broodmare-sire, Rock Sand, who was 5x5x5x5-Pocahontas! Large doses of Pocahontas, and a few other top broodmares, later filled the pedigrees of the best 20th Century racehorses.

Another alternative may be to simply load a pedigree with a variety of great broodmares closer-up. This requires less distant pedigree study and homework, but has produced many top racehorses as well as top breeding horses. Nasrullah, Turn-to, Buckpasser, Storm Cat, Sadler's Wells, A. P. Indy, Unbridled, and Seeking the Gold, among others, all feature pedigrees loaded with exceptional broodmares. And slightly lesser racehorses like Relaunch (In Reality), Successful Appeal (Valid Appeal), Swiss Yodeler (Eastern Echo), Grand Slam (Gone West), Elusive Quality (Gone West), Saint Ballado (Halo), Formal Dinner (Well Decorated), and Malibu Moon (A.P. Indy), likewise had pedigrees filled with great broodmares and have all made exceptional sires.

In the early 20th Century four foundation broodmares in particular left their stamp upon the breed: Mumtaz Mahal, Selene, La Troienne, and Plucky Liege. Mumtaz Mahal became the second dam of both Nasrullah and Mahmoud, as well as the third dam of Royal Charger. Her influence is thus found in the pedigrees of Northern Dancer, Mr. Prospector, Turn-to, and particularly Sadler's Wells, Seattle Slew, and his son A.P. Indy (6 strains of Mumtaz Mahal). In fact, Slew was among the first to feature all four of these key broodmares in his pedigree, and A.P. Indy has multiple strains of all four!!

Selene was the broodmare of three top sires in Hyperion, Sickle (whose male line descends to Mr. Prospector), and Pharamond II (whose male line descends to Buckpasser. And it's noteworthy that Buckpasser himself descends from the immediate family of La Troienne and features three of these key broodmares close-up. Seattle Slew has two strains of La Troienne, and A.P. Indy has three, (with a second dam by Buckpasser.)

Plucky Liege was the dam of three important sires herself, in Sir Gallahad III, Bull Dog, and Admiral Drake. The outstanding racehorse and sire, Roberto, remarkably features each of these three sons, and is linebred 5x5x7x5-Plucky Liege, as well as 6x5-Mumtaz Mahal.

The beauty of such broodmare power is that breeders of limited means can load their pedigrees with fine broodmares without the need to go to the most expensive stallions or mares in their breeding efforts. Blending grandsons and granddaughters of A.P. Indy, Storm Cat, Gone West, Unbridled, and Seeking the Gold, etc. in a pedigree can often achieve this end without great expense to the breeder.

As far as the exact placement of such key broodmares in a pedigree, there appears to be no strict formula for this and history shows a variety of placements in the pedigrees of top horses. But a few spots may be more advantageous than others. Mitochondrial DNA is only transmitted by mares, never by stallions, so such desirable DNA can only come from the bottom-line of a pedigree (the direct female family).

The X-Chromosome, which mares tramsmit to all their offspring, but stallions only to their daughters, can be traced fairly accurately through the bloodlines of a pedigree...One path in particular has become known as "The Heartline", because the X-Chromosome has been shown to influence the size and function of the heart in horses. The heartline traces on a zig-zag pattern to the dam, then to the dam's sire, then to his dam, and her sire, etc... So great broodmare-sires like Sir Gallahad III, War Admiral, Buckpasser, Alydar, and Secretariat might well have benefitted from an outstanding X-Chromosome that they transmitted to their daughters, but never their sons (who had far less success at stud).

And scientists are finding more and more "master genes" which have the power to turn "on" or "off" other genes, even genes on distant chromosomes. Since most Thoroughbreds have very similar genetic make-ups, it could well be that just a few such master genes could account for the long-term dominance of a mere handful of key stallions and broodmares...In fact, university experiments with fruit flies have succeeded in creating a race of super athletic, intelligent, and healthy flies by altering a single "master gene".

History shows us that sires and broodmares who enjoyed unusually large doses of these key ancestors have often enjoyed remarkable success at stud, while those bloodlines that that lacked them usually faded away... Since stallions can sire hundreds of offspring, such key broodmares are most often found through their best sons at stud, although again this varies.

A. P. Indy, Storm Cat, Gone West, Dehere, and Chief's Crown all have Secretariat as their broodmare-sire, and thus enjoy his outstanding dam, Somethingroyal, as well. In future we will surely see this group of stallions combined in pedigrees that load up on the blood of Somethingroyal, particularly when the blood of her other fine son, Sir Gaylord, is added to the equation (as it is already in A.P. Indy, whose dam is 2x4-Somethingroyal).

More than simply doubling up on fine ancestors in a pedigree, such deep linebreeding also sees the blood of these ancestors refined and filtered for quality through selection for several generations. Meanwhile, other bloodlines with strong affinities for these key ancestors will be added to the equation, creating a consistent recipe for success...

-Jay Leimbach