Thoroughbred breeding theories

Volume Six of the General Stud Book (1857)

Volume Two of the American Stud Book (1873)

Thoroughbred horse breeding theories are used by horse breeders in an attempt to predict successful mating of racehorses to produce progeny successful in horse racing. They stem from the belief that careful analysis of bloodlines, particularly the female line, can lend predictability to the breeding process. The best-known classification system was developed in the last 1800s by an Australian named Bruce Lowe, who analyzed the statistics of major race winners and ranked the distaff or mare lines by their degree of success. This and similar ranking systems are still used by some breeders today, though a prestigious pedigree does not necessarily translate into racing success.

The female line

Thoroughbred horses are traced through the distaff line, also called the mare line or tail-female line. This maternal line known as a "family". This practice dates to the beginning of the General Stud Book (GSB). This was done because the mares produce far fewer foals than stallions.

However, modern genetic studies have revealed that there are some cases where the haplotype in the mtDNA of modern Thoroughbreds differs from the stated dam line, suggesting that some records contain errors.

Many horses were inbred in the early years of Thoroughbred development, which increased the chances of early horses appearing in many pedigrees today. One example was Old Bald Peg placed in family 6, one of the earliest tap-root dams, having been foaled around 1635. Most, if not all modern Thoroughbreds trace their ancestry to her through one or both sides of their pedigree.

Origins

Around 1895 an Australian, Bruce Lowe, wrote: “Breeding Racehorses by the Figure System”. He formulated a system of family numbers from the mares listed in the General Stud Book. Lowe believed that the three foundation sires of the Thoroughbred were successful largely due to the mares they were bred to, and so predicting race horse quality required identification and assessment of the mare lines. Lowe stated,

The figures are derived from a statistical compilation of the winners of the three great English classic races, Derby, Oaks and St. Leger. The family with the largest number of wins is No. 1, the next No. 2 and so on up to No. 43, and include families whose descendants have not won a classic race.

During the 1950s Kaziemierz Bobinski and Count Zamoyski produced Family Tables of Racehorses, commonly known as the Bobinski Tables. This work expanded Bruce Lowe's numbering system of 43 families and identified a total of 74 families tracing to mares in the GSB. They identified mares in several countries whose pedigrees had been lost or whose descendants were unacceptable to the GSB at the time of Lowe’s work. Bobinski later updated his works and split Lowe's families into sub categories.

Analysis and use

Old Bald Peg, dam of the Old Morocco Mare (c.1655)

Thoroughbred families include the following:

• Families 1-43 are described by Bruce Lowe's Breeding Racehorses by the Figure System
• Families A1-A37 descend from Sanders Bruce's American Stud Book, with mares who cannot be traced to Weatherbys General Stud Book (GSB)
• Families Ar1-Ar2 are Argentine families
• Families B1-B26 trace directly to F.M. Prior's Half-Bred Studbook
• Families C1-C16 are described in the Australian Stud Book as approved Colonial Families
• Families C17-C33 descend from Australian and New Zealand mares who cannot be traced to the GSB
• Families P1-P2 are Polish families

Today, these numbers often follow a horse’s name in sale catalogues and pedigrees, much like a numerical surname and are used for checking the accuracy of pedigrees and comparing the contributions made by various mares and families. Horses that come from more highly respected families will usually command better prices than those from less respected bloodlines, although they may not prove to be better as racehorses or sires/broodmares.

See also

• Thoroughbred
• Horse breeding
• Average Earnings Index (horse racing)