Genetic Compatibility

Michael Goodbody is the managing director of Gainsborough Stud Management near Newbury, England. He delivered the following speech to the Thoroughbred Breeders Association (TBA) at its annual awards dinner in London on Jan. 7.

I would now like to touch on the important points that breeders should consider when planning to mate their mares with the object of producing high-class racehorses.

All mare matings should be basically designed with an appreciation for genetics. First and foremost we seek genetic compatibility with matching sire and dam. Without the compatibility between the strains we would be unable to upgrade the progeny's performance levels, constitution, and physique. Unfortunately for all racehorse breeders, a multitude of weak hidden genes exists in the Thoroughbred gene pool; weak, recessive genes are present in the best Thoroughbred strains found in Europe and North America. Only by the use of clever selection skills may we keep this problem in check. Genetic probability affects all matings and may be kind or cruel, and Thoroughbred breeders must accept the whims of genetic variation.

Stallions for the mares must be accepted on the basis of their unique genotype and physical types. Usually matings should be based on principles that reinforce specific ancestors for a reason, i.e., ancestors have the ability to help improve or correct conformation.

To be able to accomplish any upgrading of racing class in the next generation, a mare requires her male partner to be absolutely compatible with her genotype, i.e., her genetic makeup. Despite the fact that you want to mate a champion race mare with a champion racehorse, the result is likely to produce a non-winner if their strains are genetically incompatible. I am sure this is the reason why during the last century, the great owner-breeders would mate their Classic-winning fillies with Classic stallions belonging to other friends, without much thought to any genetic compatibility, with a result that the progeny seemed to get slower and slower. You only have to scrutinize select sales catalogues to find group I-winning mares with very ordinary produce records.

Proven Sires--As many proven sires as possible should be used during a mating plan. This is only logical if you consider that for every 15 horses that retire to stud, only one will be top class. You only have to look at some of the great racehorses over the past who were complete failures at stud such as Arazi, Spectacular Bid, and Tulyar to name just a few.

Soundness, temperament, breathing, and bleeding--In the majority of these four cases there is a problem of heredity transmission, and unless you have a very strong reason for keeping mares with any of these characteristics, or using stallions that are likely to pass them on to the progeny, this should be avoided.

More and more emphasis must be placed on soundness. Having personally bought a considerable number of yearlings over the years, overcorrection can cause more problems than is generally known. Nature will decree that if a Thoroughbred wants to turn-in or toe-out that is the way it should be. To overcorrect these faults causes major problems when the yearlings go into training and are put under pressure. Some of the worst conformed horses are sometimes the best racehorses. When Real Quiet was sold as a yearling at the Keeneland September sale for $17,000, he went on to win the Kentucky Derby. The deviation on his forelegs were so bad that a picture of his front legs appeared in The Blood-Horse as an example that horses do not have to be 100% correct to be great individuals with racing ability.

The strength of the female line--It is well known that the best stakes families usually produce quality racehorses that remain sound, with great racing ability. It is so important to have good female lines with the inherent genetic pool to draw on. Very seldom do top-class race mares with obscure pedigrees and no bottom line become foundation broodmares or even produce anything of any ability. It is usually the unraced half-sister to a champion, or a daughter of a champion, which turns out to be the better broodmare. This is undoubtedly because the genetic pool is there to draw on and when mated with the correct sires, produces good results. Perhaps the greatest breeder of modern times has been the Aga Khan, and if you study his female lines, they all go back for generations to famous foundation mares such as Mumtaz Mahal and Lady Juror. Even though this may be six generations back, they still have a lot of influence from the genetic pool and account for the continual success of his studs, even though a lot are not fashionably bred. Most matings should involve multi-duplications of very influential mares such as Mumtaz Mahal, Lady Juror, Plucky Liege, Lalun, and La Troienne.

Pedigree research of group I and grade I winners supports this strategy, and matings should be designed to involve combinations of superior brothers and sisters or three-quarter siblings to create a degree of pre-potency. For instance, line-breeding to Derby winner Sainfoin and his full sister Sierra (dam of the sprinter Sundridge) has spectacular results. This brother and sister combination occurs way back in pedigrees, but because of its dominance, it persists through the generations and should be exploited to full advantage. Duplicating maternal strength is a method used to try and manipulate the genes. I think it is most important for breeders to try and introduce powerful female lines from other successful breeders into their broodmare portfolio, hoping that some of these fillies will become group I-producing mares, and breed stallion sons to perpetuate their influence. There is a strong theory that living cells derive their energy from tiny organisms called mitochondria, transmitted in the female line, and I believe that stakes-winning families transmit more mitochondria per cell than do inferior female lines.

Sadler's Wells, of course, is out of a daughter of Bold Reason, who is by Hail to Reason out of Lalun. When he covers mares possessing the strain of Lalun's best son, Never Bend, racing class is immediately upgraded in the progeny. A combination of the two best sons of Lalun partially explains the genetic affinity that exists between Sadler's Wells and mares carrying Never Bend. We all know now how well Sadler's Wells does with daughters of Darshaan, extending from Never Bend's line and tracing in direct female line to the in-bred mare Tourzima.

The importance of the broodmare sire--The importance of retaining mares by high-class broodmare sires is recognized. Whenever the genetic makeup of a young stallion is studied, strict attention must be paid to the broodmare sire. Sires such as Darshaan, Machiavellian, Sadler's Wells, Diesis, etc., transmit superior sex-linked genes via their female offspring. Machiavellian, for example, is in-bred to the famous mare Almahmoud, an elite genetic influence.

Genetic mix--When two different strains unite to consistently create superior racehorses, we call this a genetic nick. For example, the Blushing Groom/Nijinsky cross has produced Fantastic Light, and the reverse produced Lammtarra. The cross with Sadler's Wells with mares from the Never Bend line has produced many winners and in particular High Chaparral, the Breeders' Cup Turf winner of last year.

Line-breeding to superior ancestors--In order to appreciate this, there is a subtle difference between in-breeding and line-breeding. In-breeding is the duplication of a common ancestor within three generations, where as line-breeding is duplication within the fourth, fifth, or sixth generations. We find that line-breeding is a more important technique, as it still has the same benefits of fixing characters, especially if we duplicate an ancestor via both sexes, meaning via sons and daughters. Finally, each mare has a pedigree pattern, which if understood, can identify numerous strengths and weaknesses, and can indicate how we might be able to upgrade the mare's next foal. Pedigree research involves investigating the conformation of ancestors; any weakness in the ancestry of a mare should be able to be corrected by selecting a suitable sire that breeds true for certain characteristics.

Faults not evident by mere inspection of parents can often be predicted by studying a six-generation pedigree. In other words, hidden excessive characters not seen by the naked eye can be identified.

Strategy of breeders should be to avoid repetition of the same weaknesses via both parents. They should concentrate on collecting strength and soundness from superior ancestors and choose from the four basic methods commonly used, namely in-breeding, line-breeding, out-breeding, and out-crossing.

Inspection of every mare's foal teaches us new information about how a mare transmits unique genetic influence. Some mares are quite dominant in the way they transmit their genotype, whilst some mares produce foals that look very much like their father, the stallion.

These are some ideas that we employ in our breeding operations which I fully realize are not practical for the commercial breeder, who has to produce for the market something that is fashionably bred and correct in order to maximize his return. However, if the genetic makeup is not correct in the long run, no top-class horses are produced and the broodmare band is subsequently devalued.

Finally, I would like to express my sincere thanks, which I am sure is echoed by everyone else in this room, for the excellent work that Nigel Elwes has done during his period of office at the TBA. I think that everyone agrees that we have been extremely lucky to have someone who has had the time, the enthusiasm, and the forward thinking to propel the TBA through the last few years. I am sure this good work will be continued equally as well by our current chairman, Philip Freedman.

About the Author

The Blood-Horse Staff

The Blood-Horse is the leading weekly publication devoted to international Thoroughbred racing and breeding. Since 1916, the staff of The Blood-Horse has served the Thoroughbred community with the highest standards of journalistic excellence to provide comprehensive and timely editorial coverage and analysis.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More