Line On Linebreeding

The concept reduces genetic variance and increases odds of predictability.

By Les Brinsfield

It did not take long for me to realize I made a serious mistake in my article on She Be Wild. Like many other pedigree pundits, I delineated the key linebreeding crosses in her pedigree as if their significance to the reader was a given. I will correct that error with a mini-tutorial on linebreeding. I will use the pedigree of Nearco, arguably the best horse bred in the 20th century by the best breeder, Federico Tesio. Hopefully, both definition of linebreeding and effective techniques for using it will be clear.

Linebreeding is the presence of an ancestor twice or more in a horse’s pedigree with at least one strain present from each parent. One can see Nearco is 3x3 to Chaucer and Rabelais, they sons of iconic St. Simon, by Galopin. Close on the heels of this duo comes a 4x4 cross of Cheery and Simona, they daughters of St. Simon. Enter a new term: sex-balanced linebreeding. Each parent of Nearco thus has a son and a daughter of St. Simon crossed and Nearco has a double sex-balanced cross to St. Simon: Pharos has Chaucer on Cheery and Nogara has Rabelais on Simona. Daughters of Galopin give sex balance with St. Simon.

Another significant key in Nearco’s pedigree is the appearance of Flying Fox. Flying Fox does double duty pertaining to sex-balanced linebreeding. He adds two daughters of Galopin, sire of St. Simon, who can be acknowledged as endemic to the breed. Flying Fox is by Orme, he a son of Angelica, she an own sister to St. Simon. It can thus be seen that crossing a brother/sister—St. Simon/Angelica—gives a son and a daughter of each parent, Galopin and St. Angela. I cannot emphasize too strongly the fact that few things, if any, are as explosive as crossing a brother and sister in a pedigree. The more prepotent either is, the better.

One might also adopt some basic principles of linebreeding: Son and daughter of common ancestor is good; one of either and two of the other is better; a brother and sister are best; and one of either and two of the other are utopian. Conspiring to get the common ancestor in the same generation is “very, very, very important,” per Olin Gentry, who left several Kentucky Derby winners strewn amongst his employers.

Our new term and breeding technique did no harm in this tribe, as Nearco ran 14 times and was undefeated.

Linebreeding reduces genetic variance and increases predictability at the direct expense of random chance. This is a drop in the proverb­ial bucket compared with all there is to know about linebreeding but it is more than enough to do some serious damage. Repeated matings become essential as they are required to produce brothers and sisters. Breeders need to learn who has full siblings, identify breeding stock carrying them, and plan matings accordingly.

One thing is certain: horses will go on breeding in kind when returned to sex-balanced lines of the prepotent ancestors from whom they descend.

It has been happening for centuries and will continue, as the only thing that can stop it is the breeders’ refusal to do it.