Last week’s blog post focused on three Thoroughbred breeding theories:

• The qualitative idea of breeding the best to the best
• The quantitative method of crunching stallion and mare statistics
• The controversial X-Factor theory

This week we explore three other theories adopted by breeders and buyers, along with their advantages and disadvantages.

Inbred or Outcrossed?

Inbreeding versus outcrossing is another controversial theory. This approach to breeding is considered one of the quickest ways to fix a bloodline’s desired characteristics, as inbred horses are the product of mating two closely related horses.

Outcrossing, which introduces unrelated genetic material to a breed line, increases genetic diversity and reduces the probability that the horse will have diseases or genetic abnormalities.

Linebreeding is used to describe milder forms of inbreeding and involves mating one or more relatives that occur more than once in a pedigree to avoid close inbreeding.

Inbred horses frequently make good breed stock, showcasing the line’s dominant characteristics such as increased speed and stamina. Outcrossed horses, such as Secretariat, can create a superior hybrid individual.

Cons of inbreeding include the possibility that negative recessive characteristics will crop up, resulting in weaker progeny, also known as inbreeding depression. When outcrossing a horse, though, breeders lose out on the good traits passed down in a line.

Whose Line Is It Anyway?

Another theory is focused on the female line, also known as the tail-female or mare line, which is grouped by families.

Based upon the listings in The General Stud Book (GSB), breeders maintained and built families tracing to a single mare. In the early years, most Thoroughbreds were inbred, and a study in 2010 found that breeders were focused more on documenting the stallions than focusing on the mares.

Bruce Lowe formulated the system of family numbers to distinguish the lines, with number 1 being the family with the largest number of wins, then 2, 3, etc.—up to 43.

In the 1950s, The Family Table of Racehorses, also known as the Bobinski Tables, was born, expanding the 43 families to 74. In 2004 the Japanese Bloodhorse Breeders’ Association issued Volume IV of The Family Tables of Racehorses.

It is generally acknowledged that horses who hail from the highly respected families command better prices, although they may not prove to be better racehorses, sires, or broodmares.

Nick Yourself

Nicking focuses on the compatibility of stallions from one male line with mares from other sire lines, where a score is assigned for the degree of affinity of the horse in question or hypothetical pairing.

These successful crosses have impacted Thoroughbred development positively. According to BloodHorse, the rating is calculated by factoring:

• The Sire Improvement Index (SII), a comparison of the percentage of stakes winners that a sire (or sire line) has achieved with mares by the specific broodmare sire (or sire line), with the percentage of stakes winners that specific sire (or those specific members of the sire line) has achieved with all other mares.
• The Broodmare Sire Improvement Index (BSII), a comparison of the percentage of stakes winners produced by daughters of a sire (or broodmare sire line) with the percentage of stakes winners from the same mares when bred to all other sires.

The resultant figure shows the stakes winner-to-starter production rate of the nick, compared to the stakes winner-to-starter production rate of the sire/sire line and broodmare sire/sire line when bred to representatives of all other lines.

A TrueNicks score of 2.0 indicates that the cross has produced stakes winners at twice the rate that the sire/sire line and broodmare sire/sire line have when bred to all other lines. These ratings are translated into bands from A++ to F.

It should be noted that nick ratings are recalculated every day to account for new foals, new starters, and new stakes winners. This ensures that breeders and buyers have the latest information available when considering their mating plans and purchases. TrueNicks notes that it generally takes several significant events for a rating to change bands.

There is some criticism of nicks and nick ratings—click here for the top 10 myths about nicking.

The Most Desirable Method

Whether the theory points to a reliance on judgment or on numbers, the key to producing successful racing progeny is clearly unclear. Success comes from looking at every possible trait, both in genetics and performance.

You could have the most desirable pairing with a resulting horse that looks great on paper but has no inner drive to win. Or worse, he meets every criterion but is injured before the race even starts.

With Thoroughbreds, however, everything comes down to breeding for one characteristic— racing performance.