HOW RECESSIVES ARE INHERITED

or gelding. Most culling is done on the basis of visible and measurable characteristics such as conformation, coat color or behavior. Of course accidental deaths and any deleterious double-recessives that happen to show up will also be culled (or will self-cull), and their bloodlines may drop out of the system.

At the King Ranch, fillies first have to pass inspection for conformation and are rated as Top, Good to Top,

Fair to Good, Fair, and No Good. The top two grades are passed to riders, while the rest are put in the remudas for work on the ranch or are sold. For example, historian Denhardt provides the following summary for the 1967 foal crop: 9 percent were rated Top, 10 percent were rated Good to Top, 45 percent were considered Good, 31 percent Fair, and 5 percent were No Good or Not Rated.

Nor are top-rated fillies bred before being tested. Most of the riders are Kineños, and, reports Denhardt, “they must gain the wholehearted approval of the riders before they are put in the broodmare bands.” Dick Kleberg observes, “Some horses tend to be ‘natural’ stock horses, just as some men are natural athletes. This trait has proven to be heritable to a certain degree, particularly if you…look for

[it] and select for it.” Bob Kleberg echoes, “Constructive breeding takes into consideration more than merely the proportion of genes of a particular type or individual in a pedigree.

It calls for the skillful planning of matings and expert attention to many other things.”

• Step 4. Bring mares surviving from Step 3 back to their sire for cover (or to their own cousins or half-brothers). While the first round

of outcross breeding brings to light conformationally and athletically superior individuals, this round of tight inbreeding greatly increases the frequency of foals who are homozygotes. This cuts both ways, as homozygosity increases for both desirable and for deleterious characteristics. When deleterious alleles are expressed in the body and behavior of the living animal, they are exposed to selection and culling--whether in nature or by the breeder. Breeders must realize that not all recessive alleles are deleterious, while some dominant alleles are harmful. Tight inbreeding may also help to expose deleterious traits that are inherited as genetic dominants.

Many foals who are homozygous for deleterious traits will spontaneously abort as embryos, fetuses or neonates. A certain further percentage will show some problem later on when assessed for conformation, soundness, physiology, resistance to disease, sexual viability or trainability. In short, in this generation of highly inbred foals, a relatively high mortality rate as well as a high culling rate is expected. Rather than being a tragedy, the deliberate exposure and subsequent purging of deleterious gene combinations must be regarded as desirable because removal of inferior and inviable foals promotes and protects the long-term welfare of the bloodline and the breed.

• Step 5. Assess and test survivors as before for conformation, physiology, behavior and aptitude for the work intended. At this stage it continues to be imperative to test both potential broodmares and stallions in actual working conditions. Some will pass these tests, while most are likely

to be middling or even poor, in which case they must be culled. Kleberg observed, “We were fully aware that not every…sire has a balance of genetic qualities which will stand the test of close inbreeding without disaster.

The only way in which this [can] be determined [is] by actual trial.”

Survivors of Step 5 trials comprise an elite cadre of mares (plus a few of their brothers) who are reserved for the next round of breeding.

• Step 6. Divide elite broodmares into two groups, one of which (“Group A”) will be bred to unrelated males who have been selected to complement them in terms of conformation, physiology and behavior. The second group (“B”) will be covered by their uncles or half-brothers (see “Purging Selection,” page 95) for a final round of inbreeding. After trials, the two groups can be swapped so that the outcome of both inbreeding and outcrossing

from each mare can be assessed.

• Step 7. Introduce unrelated broodmares with desirable characteristics that may not have been present in the founding manada. Between 1935 and 1970 more than 50 Quarter Horse mares adjudged good enough to go into the breeding program were purchased by the King Ranch. Bob Kleberg states that “All introductions of new blood were made not for the [mere] purpose of securing new blood, but to bring into the strain exceptionally fine qualities of individual mares.” The King Ranch has continued to purchase unrelated, quality Quarter

Horse mares, and Kleberg reported that “In all cases new Quarter Horse blood has been introduced through the female line.”

• Step 8. Breed sane, sound horses. The pattern of inbreeding followed by outcrossing will continue to produce excellent livestock only so long as the breeder maintains the overall goal of producing not “performance specialists” but allaround useful individuals. Testing must remain meaningful and some foals must be culled in every generation. This means that a use other than breeding must be found for three out of every four foals produced, whether they are colts or fillies---and this is exactly why the main breeding goal should be to produce all-around useful horses that ordinary people can handle and enjoy!

ASSESSMENT AND TESTING

The importance of assessment and testing---which also implies accurate record-keeping---cannot be overstated.

There must also be an utter lack of skulduggery and silliness, for example passing inferior colts and fillies and funneling them to competitors in an effort to guarantee that they breed from inferior bloodstock, or breeding from an inferior mare because somebody wants to raise foals just because they’re cute. In short, in an ideal world the overriding concern is always to maintain the long-term health, soundness and viability of the bloodline and of the breed as a whole.

Kleberg warned in 1946, “The problem [of avoiding excessive inbreeding] will become more complex when the AQHA closes its books so that further outbreeding to unregistered animals must stop. Such animals contributed very materially to the development of the modern Quarter Horse, and the elimination of this source of new genes will necessitate a more intensive use of superior individuals and strains within the breed.” We note in hindsight that since its inception the AQHA has gone back and forth concerning this question and finally during the late 1980s developed a workable policy of “appendix registration” which allows non-Quarter Horses to enter the studbook by proving themselves superior in various performance contexts.

Appendix registration represents a system of testing. Testing is meaningful

only when it involves competent riders and handlers using horses in realworld working contexts. Bob and Dick Kleberg emphasize that the breeder must have an intimate knowledge of the individual horses. The more aspects that horses are tested and rated upon--that is, the more “selective factors” that are considered---the more the breeding program will resemble nature, and the higher the chances of consistently producing sound animals who are durable, reliable all-around performers. In a recent telephone conversation James Clement III, current head of the King Ranch breeding program, assured me, “that’s what we’re breeding for now. After [Bob Kleberg died in 1974] we tried halter showing and reining and of course we continue to be spectacularly successful in cutting. But the main, overall goal these days is to produce good horses that the average cowboy can handle and enjoy.”

Since the end of WWII, this objective---central to Kleberg’s original breeding program---has become increasingly rare because working farms and ranches, along with other real-world working contexts for horses, have become rare. In all breeds today, successful show competitors are specialists with spectacular performance capabilities within narrowly-defined disciplines, but they are often delicately made, congenitally unsound, or mentally flighty so that they require expert handling and riding. As the above breeding protocol makes clear, flashy performers can be produced via tight inbreeding in only one or two generations, but when a breed comes to be made up primarily of such horses, it is doomed. As the Klebergs say, it takes meticulous care, a great deal of knowledge and a dose of humility to breed great horses. And, depending upon luck and resources, it may take twenty equine generations ---more than two human lifetimes---to accomplish it.

ROUTES TO FAILURE

There is voluminous scientific literature reporting the effects of allelic diversity and gene pool size, genetic drift, breeding bottlenecks and selection as they operate on wild animals in nature. Principles derived from these studies apply equally to domestic populations, which can be regarded as ecosystems in miniature. Study of breeding within natural populations warns breeders of certain routes to failure:

• Breeding for a single characteristic such as racing speed, head shape, length or refinement of the neck, ability to lift and

fold the knees, or coat pattern or color. When a single factor is used as the sole criterion for inclusion of an animal for breeding purposes, other factors more important in the long term---such as soundness, the strength of the immune system, or the ability to produce viable sperm--inevitably suffer.

• Breeding to construct a “fashionable” pedigree, especially where the fashionable names all go back to a single sire (i.e., the breeding program contains mares that are all related to each other). This is often motivated by profit, but breeders who put profit ahead of genetic diversity and quality have it backwards! Sound, sane, well-conformed horses are always in great market demand; the breeder who aims to produce these will also get some superior performers who can be sold for more money to professionals.

• Misuse of artificial insemination. Artificial insemination (AI) is a two-edged sword: Potentially it permits wide testing of a desirable sire; but in dog as well as in horse breeds where it is allowed, it has too frequently been misused as a guarantee of fashionability and profitability. Registries which permit AI must put teeth into rules that require periodic outcrossing to unrelated animals.

• Breeding without meaningful assessment of conformation.

The “halter classes” of many American breeds today identify popular horses, but they do not reward conformationally superior or even structurally correct individuals. Examples of breeds that today require meaningful conformation assessment for registration are the

German and Dutch Warmbloods and the Peruvian Paso.

• Breeding without testing for performance capability.

• Clinging to wrong genetic concepts. The science of genetics is complex and breeders and buyers can get confused. For example, as useful as DNA is for confirming parentage and identifying genetic diseases, horses are bred by observing conformation and behavior, not “by DNA.” In recent correspondence, geneticist Phil Sponenberg, DVM, PhD, pointed out another misconception: “Kleberg seems to have liked sorrels/ chestnuts (a recessive) so that they became common. Many folks seem to think that such alleles then magically become dominant!”

To summarize: Prevalent does not equate to dominant; all recessives are not deleterious; all dominant alleles are not advantageous. Geneticist William G. Hill, writing in a 1995 edition of the journal Genetics, points out that much success in breeding is attributable to “luck” because of genetic linkage, the tendency for functionally similar groups of alleles to be inherited together.

This is frequently supplemented by pleiotropy, which occurs when genes interact to produce “good nicks”--effects in the living animal that are greater than the sum of the effects of the individual genes.

• Breeding within too small a broodmare population. This raises the question of whether small breeds, and individual small breeders, can survive economically and contribute in a positive way to the long-term viability of a breed. While it is possible to hit the jackpot with a single breeding, a much wiser plan is for

small breeders to band together in the spirit of cooperation, creating affordable and practical means of access to multiple broodmares and multiple sources of semen. Small breeders must insist upon breed registries with open studbooks that welcome a diversity of types within the breed definition, while promoting meaningful training for livestock judges so that they have a knowledge of anatomy and conformation and a feel for temperament and trainability.

• Continued inbreeding without outcrossing. As “Sewall Wright’s Table of Relatedness” (page 88) shows, no matter what inbreeding

(or “line breeding”) program is employed, they eventually all result in 100 percent fixation of recessive alleles, some of which are for desirable characteristics but many of which are deleterious. Sewall Wright proved that precisely because they are recessive, deleterious alleles are unlikely ever to be completely purged from the population.

Bob Kleberg observes, “These considerations will be much more important in succeeding generations as Old Sorrel and his sons and daughters recede into the background. By intensive inbreeding it is possible to retain a high degree of relationship to a noteworthy foundation sire for many generations.” This does not mean, however, that inbreeding should be the whole program!

This misconception comes from Sewall Wright himself, who stated in 1921 that “Matings between relatives more remote than first cousins have little significance as inbreeding …” ---an idea that has led many recent breeders to believe that pedigrees which lead back in as many as half of their bloodlines to a single sire are not dangerously inbred! (See my reports on American Pharoah and Justify in EQUUS 458 and EQUUS 494.)

Breeders must read Sewall

Wright’s whole statement: “Matings between relatives more remote than first cousins have little significance as inbreeding except in so far as there is continued breeding within a population of small size.” In other words, matings between relatives matter hugely when the diversity of alleles in the population gene pool is much smaller than a short pedigree may seem to indicate---because all first cousins actually trace back to only one or a few ancestors. In such a herd, all individuals are inbred, and if breeding is confined to that gene pool, the only foals that

can be produced will be inbred!

• Breeding by rote or formula.

The breeders must not merely be investors, but either ride well themselves or be the hands-on supervisors of employees who ride and train their horses.

Bob Kleberg writes, “The breeder who attempts to work by formula or by rote is inviting disappointment and almost certain disaster.” The application of mathematical formulas to real-world animal breeding--which involves living things---must always be tempered by common sense seasoned with humility. Probably the single most important thing that Kleberg learned from the genetics and animal breeding lectures which he attended was this aphorism of Sewall Wright: “An organism must be viewed as a vast network of interacting systems.”

Living creatures defy complete categorization because they are awesomely complex. “Biometrical tools such as coefficients of inbreeding and relationship are not magic formulae which of themselves will assure the success of a breeding program,” writes Kleberg. “Linebreeding and other types of inbreeding are not of themselves capable of assuring automatically any particular results. The only effect of the concentration of genes through inbreeding is to fix a type. Whether the type that emerges is more or less than the average will only be determined in the long run by the actual outcome of individual matings. The skill of the breeder and his care in the choice of individuals as foundation stock and in the planning of individual matings remains the all-important part of any breeding program.”