97 Update
More Information
Contacting Us

Linebreeding vs. Inbreeding


By Roger Lyons
A version of this article originally appeared in OwnerBreeder journal, January 2000.

       The term “linebreeding” is frequently used as a reference in Thoroughbred breeding to duplications of ancestors occurring beyond the fourth generational remove. In livestock breeding, however, the term “linebreeding” has a more specialized usage. An individual is considered to be linebred when both parents have multiple occurrences of the same “line” within pedigree space that is considered useful. The purpose of linebreeding, in this sense, is to select one trait that happened to be uniquely expressed by that line. Because of the uniqueness of that line’s contribution, any incidental duplications of other ancestors would only detract from the effectiveness of linebreeding. This is why the extent to which an individual is considered linebred depends upon the avoidance of such incidental duplications.
       Clearly, the term “linebreeding” as used in discussions of Thoroughbred breeding has a trivialized denotation. It’s nothing more than a matter of generational distance. At first blush, the prevalence of this usage in discussions of Thoroughbred breeding seems harmless enough, but it happens that understanding the function and purpose of linebreeding, in its specialized sense, is crucial to understanding a fundamental difference between Thoroughbred breeding and livestock breeding, a difference to which Thoroughbred breeders, generally, are not nearly attentive enough.

How to breed a pig with big ears
       Let’s say you want to breed a pig with really big ears, and you don’t care what that pig looks like apart from that. You just want to show off those colossal ears. You want to enter your freakishly big-eared pig in one of those geek livestock shows that make the drive across Kansas on I-70 so enjoyable, along with other attractions, such as the World’s Largest Prairie Dog Town and, of course, the scenic overlooks. Or you might just want to invite your neighbors over to stand around and gape in amazement at those enormous lobes. You don’t intend to enter that pig in any swine racing events or, heaven forbid, in a barbecue competition, for which those ears, in the former case, would be an impediment and, in the latter case, almost unexploitable. We’re not trying to account for taste, but only for the breeding method that would work best if, for reasons all your own, you want elephantine ears on a head that looks at least remotely piggish.
       Let’s say you have a sow that is ugly to an extreme, but has lugubriously large ears, and you figure that she has those gargantuan ears because she is inbred to an ancestor whose ears are legendary. You also happen to have a hog who is just as gifted aurally as the sow, though a bit obtuse, and is inbred to that same ancestor. The offspring of these two would be linebred to that ancestor whom you believe to be the prime source of humongous ears, and, though most of the offspring would not meet your standard for auditory apparatus, one of them might be a hit on the picture postcard racks off I-70.
       How frequently ears of monumental proportions would turn up, so to speak, among offspring would depend on the strains of descent of that ancestor to which you are linebreeding. Suppose, for example, that among the four strains of descent there was one that passed on superior intelligence, but hopelessly ordinary ears. This particular strain would lower the frequency of occurrence of expansive ears in the offspring. Linebreeding works best when the trait you are selecting--in this case, ears that look like mud flaps--is consistently expressed through all strains of descent of the ancestor to which you are linebreeding. Obviously, if none of the strains of descent of that ancestor expressed his or her mammoth ears, then linebreeding to that ancestor through those strains would be utterly useless.        

Inbreeding or linebreeding?
       If you surf the web for pedigree analyses of Anees, you will find it routinely written (in cyberspace, not stone) that he is inbred to Raise a Native and linebred to both Nasrullah and Princequillo. This would seem nonsense to the livestock breeder. In the first place, if Anees is inbred to Raise a Native, he couldn’t possibly be linebred to some other ancestor. In the second place, he can’t be linebred to two different ancestors since linebreeding, by definition, targets only one ancestor. But, worst of all, the livestock breeder will have some head-scratching to do over the absence of any mention of the trait that is being targeted by this so-called linebreeding.
       When breeding for non-performance values, as in animal and plant husbandry, you are usually selecting a particular trait, often sacrificing others. It has recently been noticed that, in the course of selection for increased size in roses, for example, the rose scent has been inadvertently bred out, much to the dismay of the market for roses. This kind of thing is legion in livestock and plant breeding, often owing to the purpose associated with linebreeding.
       Since speed in the racehorse cannot be reduced to a trait--or even a definite set of traits--that a breeder could select by way of linebreeding, it is obvious that linebreeding--in the strict sense illustrated by the gigantic rose that has no scent and by the pig that has huge ears but just might be deaf--has no value whatever in Thoroughbred breeding.

Aptitudinal diversity
       The breeding methods used to breed a racehorse are fundamentally opposed to the breeding methods used to breed livestock. Since Thoroughbred breeding is oriented towards performance, it is not concerned with selecting traits of relatively distant ancestors, but rather with selecting aptitudes. Moreover, while the central problem of livestock breeding is to find ways to select a particular trait, the central problem of Thoroughbred breeding is to find ways to blend a variety of aptitudes in a single individual.
       Despite complaints about the lack of superstars, today’s major racing environments are highly competitive. Witnesses to the last Breeders’ Cup Day could credibly testify that we now have more really good racehorses than ever before. In such a competitive environment, it is no longer enough for a sprinter to be just a sprinter or a stayer to be just a stayer. Today’s racehorses, especially those that compete in the classics, must have speed, acceleration, stamina, and the will to win, and they must have all of these aptitudes in more or less equally abundant measure. This is why fixing type by way of linebreeding methods is no longer a viable approach to breeding a racehorse, and this has been the case for most of this century.
       The most obvious way to blend contrasting aptitudes is to outcross. Unfortunately, most outcrosses fail, and the reason for this is that the contrasting aptitudes conflict with one another, rather than blend. Paradoxically, inbreeding is the most effective solution to the problem of blending contrasting aptitudes. Because of developmental conditions in the breed during the 20th century, certain ancestors have been notable for the aptitudinal diversity of their respective strains. When inbreeding to such ancestors through strains of contrasting aptitude, inbreeding functions, in that respect, opposite its function in livestock breeding. While inbreeding to such ancestors will unavoidably select certain traits, both favorable and unfavorable, the shared genetic background of the strains will also contribute to a favorable blend of their contrasting aptitudes.
       This approach is evident in the case of Anees, who is distinctly an inbred individual. Raise a Native is duplicated 3x4 through the patently brilliant influence of Mr. Prospector and the classic influence of Alydar. He is inbred 6x5x5 to Nasrullah through stout Nashua, stamina-oriented On-and-On, and Natasha, whose descendents have proven remarkably dynamic in influence, as demonstrated by the sprinter Capote Belle, whose fourth dam is Natasha.

Transformations of influence
       Inbreeding through strains of contrasting aptitude is the dominant method of producing good racehorses for today’s major racing environments. The ancestors that currently occur within the most effective generational range and are most frequently duplicated in the best racehorses happen to be the very ancestors who descend through the most diverse array of aptitudinal types, including Raise a Native, Northern Dancer, Bold Ruler, Nasrullah, and even Princequillo, who is not, as is often supposed, strictly a stamina influence.
       With all due respect to the Bruce Lowe family numbers, the aptitudinal expression of female ancestors, like that of male ancestors, is determined to some extent by the succession of crosses through which that ancestor descends to the new individual. Princequillo descends to Anees 6x5x6 through Cequillo, Somethingroyal, and the sire Dedicate. Cequillo descends to Anees through speed, involving Correlation, who stood with Needles at Bonnie Heath Farm in Ocala, and Mr. Prospector. Somethingroyal, by contrast, descends through stamina influences Sir Gaylord and Sir Ivor.
       Generally, ancestors who have been prepotent to a relatively narrow range of type, such as Nijinsky II, Damascus, His Majesty, Graustark, Spy Song, and many otherwise important sires, have not served well as targets for inbreeding. Indeed, inbreeding to these ancestors gravitates in the direction of linebreeding, precisely because these sires do not descend through aptitudinally contrasting strains.
       The crystallizing effects of these ancestors, however, can be ameliorated by generational distance, which increases the likelihood that the contributions of these ancestors will become vulnerable to variation resulting from the successive crosses through which they descend. Consequently, the quality of runners inbred to such ancestors tends to improve as those ancestors become more generationally distant and the debilitating effects become more innocuous.
       When breeders are inattentive to the aptitudinal potentials of the strains through which they inbreed to the most influential ancestors, they risk breeding out aptitudinal expressions that are crucial to successful performance. The last thing you want to do is target an ancestor who descends through strains that all passed on a similar aptitudinal expression to their offspring, as is done in the case of linebreeding. Inbreeding through strains of contrasting aptitudinal expression is the most successful approach because it tends to broaden the aptitudinal scope of the new individual.

Copyright © 2000 Roger E. Lyons
Web queries should be directed to CompuSire's WebMaster.