What Is An Outcross Breeding

by Paul F. Spears 2/3/2011

In my last blog, I explored the idea that inbred or consecutively linebred broodmares should be mated to “outcross” stallions. As I finished the article, I thought about the difficulties in defining an “outcross” breeding. North American Standardbred horses have become so inbred that our concept of an outcross will be much different from that of a Thoroughbred breeder. Thoroughbred breeders traditionally avoid common ancestors in the first five generations, usually resulting in an Inbreeding Co-efficient of 1-2% in this part of the pedigree. Such an approach is now virtually impossible in Standardbred trotters. We are now firmly on a course to additional inbreeding, whether we like it or not.

In North America, the Axworthy trotting stallion line has almost vanished. Sierra Kosmos is old, unappreciated, and neglected. Our breeding choices now come from three major sire lines – Speedster, Noble Victory, and Star’s Pride. Even these sire lines diverged only a relatively short time ago. Foaled in 1926, Volomite is the grandsire of both Noble Victory and Star’s Pride. Although the Speedster line diverged earlier, all three lines originated from Peter The Great, foaled in 1895. Peter The Great is in the 7th generation of the sire line of Andover Hall, the 7th generation of the sire line of Credit Winner, and the 12th generation of the sire line of Muscles Yankee.

So, when we speak about “outcross” matings in our corner of the equine world, we are simply discussing matings that don’t immediately duplicate bloodlines toward the front of the pedigree.

We refer to a horse as “linebred” or “outcrossed” based upon the sire lines of its own sire and dam. However, for inheritance of traits that are not sex linked, the position of the ancestor within a single generation of a pedigree probably does not matter. Genetically, a 4×4 cross results in the same amount of line breeding no matter which positions those individuals occupy within the 4th generation of the pedigree. I personally believe that if you are going to line breed, maternal line breeding in X position may give additional benefits for any positive sex linked traits, while relative outcrossing of the main sire lines will help to preserve genetic diversity.

When I talk about outcrossing, line breeding, and inbreeding, I use Jim Harrison’s definitions from the original “Care and Training of the Trotter and Pacer”: the sum of generations of duplicated individuals is 6 or less for “inbred” matings to that individual; the sum is 7 or 8 for  “line bred” matings; and the sum is 9 or greater for “outcross” matings.

While line breeding focuses on relationships of individual ancestors within the pedigree, the Inbreeding Coefficient (IC) is a useful tool that broadly measures the amount of inbreeding throughout the pedigree. The Inbreeding Coefficient can be defined by either a segment of the pedigree (as Thoroughbred breeders often do, when examining the first 5 generations for duplication), or the entire pedigree as far back as ancestors are known. Blodbanken.nu defines the Inbreeding Coefficient as half the common ancestry of the individual’s parents; genetically, it refers to the average chance that any gene pair will be homozygous (the same). Virtually all North American trotters are now inbred. My own 17 broodmares with complete pedigrees listed in Blodbanken have an average IC = 13.59%.  Broadly speaking, matings that lower the Inbreeding Coefficient can be described as relative “outcrosses”, and the amount by which the Inbreeding Coefficient is lowered can be seen as a measure of the degree of the outcross. For example, the mating of a stallion with IC = 15% with a mare with IC = 15% might result in a relative outcross foal with IC = 12% if the two parents have very different line breeding. A mating that is has a lower IC than the average IC of the overall population can be described as a mating that is an outcross relative to the overall breeding population. Therefore, we can use the Inbreeding Coefficient in many creative ways when making our breeding decisions.

This discussion is very technical, but illustrates the challenges we face when breeding our horses. In general, we must be careful to preserve genetic diversity in our horses, and look for outcross opportunities when we can identify them. In general, outcross strategies often result in better performance when applied to an inbred population. Because of the extensive inbreeding of North American trotters, we must be alert for opportunities to promote new bloodlines. Unfortunately, commercial buyers do not often understand these issues. Breeders who take novel approaches with bloodlines may need the courage to prove their theories by racing their horses themselves. Major outcross possibilities for North American trotters could come from several possible sources:

  • French bloodlines. North American bloodlines have already had a major positive impact on French trotters. Scandinavian breeders are introducing French bloodlines into their matings, and have achieved considerable success. Conny Nobell (IC = 8.48%), Maharajah (IC = 10.42%), Gidde Palema (IC = 5.15%), Offshore Dream (IC = 1.42%), and Commander Crowe (IC = 5.28%) have been great racehorses with significant French bloodlines. In the US, Revenue S-sired Break The Bank K (IC = 7.49%) demonstrated early speed and superior ability. Although US breeders have not used French bloodlines extensively, the racing successes of M. J-P DuBois may change our thoughts. From limited opportunities, Taurus Dream has already sired Crys Dream 2, 1:54.3 ($584,392), Val Taurus 3, 1:53.2 ($362,444), Flora Dream 1:54.1 ($307,345), Intense America 2, 1:54.4 ($137,405), etc.
  • Scandinavian bloodlines. Although intermixed with North American bloodlines, Scandinavian horses have evolved in somewhat different directions. Some stallions that have flourished in Sweden may have sire lines that were less popular in the United States. For example, Nevele Pride has been very influential in Sweden. In the US, Nevele Pride’s influence has been largely through Bonefish in maternal pedigrees, though of course he has re-emerged in the sire line of Kadabra. “Old” Scandinavian bloodlines predate such pivotal North American horses such as Speedster and Star’s Pride. Descendants of such stallions present a fine opportunity to re-establish these bloodlines in the US.
  • Pacing bloodlines. Majestic Son (IC =10.47%) and Trade Balance (IC = 7.01%) are good examples of trotters that successfully incorporated pacing bloodlines. In particular, Volomite is an active bloodline for both trotters and pacers. Rocknroll Hanover and Somebeachsomewhere both have significant Volomite bloodlines. Perhaps matings of their daughters with trotting sires would be rewarding, if anyone has the courage to train those horses as trotters.

As a North American breeder, I am interested in the pedigree of the current Swedish star Maharajah. Maharajah  has many attractive characteristics:

  • His sire Viking Kronos not only has been dominant in Sweden, but also comes from the Volomite sire line that would outcross Valley Victory and Noble Victory broodmares in North America.
  • His second dam Stevie Nicks is by the French sire Tibur, giving him a small dose (10.28%) of French blood to improve genetic diversity.
  • His bottom maternal line is old Swedish blood, again presenting an outcross for North American bloodstock.
  • He won two major Swedish races at 3 (Criterium, E3 Final), and has only improved with age.
  • He is of medium size and build, to appeal to a wide range of mares.

Perhaps Maharajah could become an interesting outcross sire for North America, if our breeders and owners can see him in action against our best aged horses?