There is a positive genetic impact when close siblings are in your sport horse lineage. Statistically, adding close siblings of important ancestors has proven to be one of the most significant pedigree designs you can create to upgrade your sport horse's potency. The power in the presence of siblings, especially full or 3/4 will be demonstrated here.
Before we begin this discussion I should define siblings for you. In the Thoroughbred industry it is common to consider siblings only in relation to the same mother and this has caused some confusion to my readers. For instance if a horse has the same sire such as two sons of Nearco for instance, with different mothers, then they are not considered siblings in the common Thoroughbred industry understanding. We are concerned however with building potency and so we won't limit our options with restrictive traditions like these because we are concerned with genetics not traditions. So if two horses have the same sire and unrelated dams for our use we will consider them half siblings.
With 3/4 siblings it is a little more complicated. Traditionally two horses with the same dam and one other common grandparent are considered 3/4 siblings. Once again here we are looking at the weight of the genetics, so if two horses have the same sire or the full brother to the sire and if the dam carries enough common ancestors for them to be 75% related then we will still consider them 3/4 siblings. Here is a good example of 'genetic' 3/4 siblings: Friar Rock, who is by Rock Sand out of Fairy Gold is genetically 3/4 related to Man O' War who is by Fair Play a son of Fairy Gold out of a mare by Rock Sand. The proof of the close sibling power in these two is seen in the great sireline of War Relic (1x2 Man O' War/Friar Rock) and Eight Thirty (2x3), these are sires and broodmare sires that still play a prominent part in the sport genetics of today.
Full siblings are self-explanatory, however we can have 'genetic' full siblings, such as when the full brother is also mated to the same dam or if a full sister is mated to the same sire then the offspring would be 'genetic' full siblings.
In a previous article we discussed the big breakthrough for Thoroughbred breeders and pedigree researchers was when they discovered that for champions they needed both the x and the y chromosome material. Even today many breeders don't value the contribution coming from the mare or from female descendants of great horses. History has shown that breeding back to only the male descendants of great sires causes some loss of ability and potency. This fact makes genetic sense to us because of the valuable components that arrive to the foal via mtDNA and on the X chromosome.
But there is more to this then just adding the female ingredient. Research has uncovered that a dramatic upgrading occurs when 3/4, 7/8 and full siblings are brought together in a lineage and sex balanced. We can thank all the Thoroughbred pedigree scholars once again for this break through. And then we can be intelligent and apply it to our own breeding decisions.
"Only by reducing the genetic pool by duplicating superior ancestors can certain gene groupings be reinforced." (McLean)
The Thoroughbred researchers, by studying the pedigrees of not only performance champions, but the individuals that have a lasting impact on the breed, it became apparent to them that siblings, especially full and 3/4, are the strongest and most lasting genetic power in the champions of yesteryear.
So let's look at how this sibling power occurs in some examples. One of the primary goals of the breeder is to develop a strong and potent type in their herd for their breeding goals. For example if we are breeding jumpers we of course want our stock to not only jump well, but be able to pass on that talent consistently to their offspring. This requires potency in jump traits, in soundness and general athleticism.
The French Thoroughbred Le Sancy (above) is an enduring jump line found throughout the European sport horse. His line has stood the test of time---although he was born in 1884, his jump line still produces great jumpers, and if we concentrate his bloodline in the background of our pedigrees we will set a nice jump type into our stock. How can a horse born in 1884 impact our stock today? Because he is potent, he is able to pass down the traits intact to his descendants. If we create a concentration of him, even back in the lineage, it will override the closer influences that are less potent. Le Sancy is so effective because he is 2x3 to the full English Thoroughbred siblings Thormanby and Lady Hawthorn, who are jump transmitters. He sets a jump type reliably.
Another incredible jump source is the English Thoroughbred The Tetrarch, who is inbred 3x3 to the full siblings Tadcaster/Clementina, jump sources (You can see his picture and a discussion on the Understanding Pedigrees page).
Pictured above in a painting by George Stubbs is another typesetter with a capital "T": The English Thoroughbred Diomed, born in 1777, imported to America when he was 21, yet he went on to become one of the key foundations of all our American horses. He is 5x5x5x5x4 to the full brothers Flying Childers/Bartletts Childers, and he is also 4x4x4 to the 3/4 siblings Sister to Soreheels/Crofts Partner--a very potent design, and he is found in multiples of all our breeds.
Another early English Thoroughbred import that left his mark indelibly on the American horse is Janus, imported in 1756, right before the Revolution. Although he raced in four mile heat races demonstrating he had stamina strength, he became noted instead for the incredible sprint speed he produced in his young, and lesser known today but well valued back then, he was renowned as a sire of excellent gaited saddle horses. He was potent for those two things. Janus was 3x4 to the full siblings Bald Galloway/Points, speed horses that gave lovely gaits. Bald Galloway's dam was a Royal Mare, which were mares from the pre-Thoroughbred racehorse studs, and they were largely of Hobby genetics, and the Hobby is a speed and gait source.
It is interesting to note that the great English sire Highflyer, who may be a root source of dressage talent, is out of a dam that is inbred to Bald Galloway and his sister as well--see Dressage champions page for more on him with his picture and pedigree.
Full sibling power structures are found in all breeds. The Holstein has the Mecklenburg coach sires Falb and Ali (full brothers) in multiples behind the majority of its lineages--see Loretto page for an example. These full brothers are largely made up of Yorkshire Coach Horse, Norfolk Trotter and Thoroughbred lines, which were breeds imported by Mecklenburg Stud to create a true coach horse type, by crossing in these breeds on the draft horse base of the continent. Falb and Ali brought in the coaching elements, along with some speed and the ability to jump which came from its Trotter and Thoroughbred components.
Above is Alkoven, a foundation sire of the Hanoverian breed. As you can see he is of the coach horse phenotype. You will find him, his full brother Alkoven II and their full sister Alonia in multiples in the background of Hanoverian lineages--they are typesetters.
This is Adios, a Standardbred super sire, an extreme typesetter. The Standardbred breed, the greatest mid-gait racing breed in the world is very potent. Adios is head of one of the most successful pacing dynasties and a line noted for its good disposition, soundness, and surprising now dressage ability, he is inbred via both parents. His sire is inbred 3x3 to the full siblings Brown Hal/Stella Hal, and his dam is 3x2 to the full sisters By Guy and Adioo.
This is Domino, the greatest modern speed line in the American Thoroughbred, and he is inbred not to sprint sources, but to extreme stamina lines--we discuss this upset to the common industry wisdom on sprint speed and its source on the American TB page. Domino is inbred 5x4 to the full brothers Birdcatcher/Faugh-a-Ballah (jump lines), 5x5 to the full sisters Cobweb/Phantom Mare, and 3x4 to the 3/4 brothers War Dance RH/Lecomte RH (stamina-jump). He is also 3x4x4 to Lexington RH (stamina-jump).
Another fine example of the undeniable power of full siblings in a lineage is Mumtaz Mahal, a mare who established a powerful dynasty and she is out of parents who are each inbred to full siblings.
With just these few examples I expect you can see how lasting potent sport sources are constructed. It is a simple concept: add more of the ingredients (bloodlines) that carry the traits you want, and you will get more of those traits in your foal. Full and close sibling designs are historically and statistically a proven road to potency.