News Letter: Winter, 2002 - 2003
On the Concept of Grading Up

Briefly, OK ... we did have the second greatest snowfall in (however brief) recorded Colorado history. So here is what 3 feet of snow was like. Now on to other things. We have had a number of questions since bringing the Australian Bond sheep into our flock about what it is we are trying to accomplish in the long term. I think our breeding program for our flock of Corriedales will be considerably enhanced by the genetics that the Bonds have to offer.

In the January issue of the "Shepherd" magazine there was an excellent article on a concept called "grading up". I am going to reprint the full article here, now, as it best explains what we are doing with our flock. Later in this news letter there will be some photos of some of this year's lambs ... our first 3/4 Bond lambs. They seem to be excellent offspring from our Corriedale bloodlines, and we are very pleased!

Grading Up Can Breed Results
By D. Phillip Sponenberg, Ph.D.
From The American Livestock Breeds Conservancy NEWS

Grading up has a lot of positives, a few negatives, and several facets that make it an interesting biological phenomenon. As a backdrop to this issue, it is important to reflect on the character and utility of breeds. Certain combinations of genes are repeated throughout a breed, and it is this consistent genetic makeup that makes a breed reasonably predictable. Predictability is key to a breed's value, for without predictability it is impossible to match a breed to place, purpose, and system. Therefore, anything that conserves the aspect of breeds as consistent genetic packages is beneficial, and, likewise, anything that detracts from it is detrimental to the breed's survival.

Often, grading up is seen as a threat to purebred stock, but in fact, it can ensure breed survivability over long centuries of purebred breeding. Understanding what grading up is and how it affects a breed genetically are extremely important issues for breeders of all purebred animals.

Grading up is the sequential use of purebred animals with grade animals over a series of generations to provide a "nearly purebred" result. The usual sequence is that a purebred sire is used on females that are either crossbred or of another breed. The resulting offspring are 1/2 the pure breed of the sire. The daughters are then mated back to another purebred sire, providing offspring that are 3/4 pure. The next generation provides offspring that are 7/8, the next 15/16, then 31/32, 63164, 127/128, and so forth.

Grading up has been widely used in a number of livestock species, especially with recently imported breeds. It allows for rapid numerical expansion of the breed, and also provides a demand for purebred males for crossbreeding.

Traditionally, grading up involves the use of purebred sires on grade dams, but it is also biologically valid to use purebred dams for this process. In light of current knowledge of the unique genetic contributions of females (mitochondria, for example), it may be best to insist on the use of both purebred males and females in at least some of the generations, in order to assure that sex specific genetic material, such as Y chromosomes and mitochondria, have come from the purebred pool.

In other words, both the sire and dam have the potential for providing genetic material that is not in the original pure breed. How much, and what this means as a practical issue, is important. Grade animals usually closely resemble the purebred at levels of 3/4 to 7/8 purebred influence. At these levels, however, they still include a good deal of genetic material that is not from the breed in question. (Realize that in all of this we are talking averages. Individual animals could be found that are either a lot more or a lot less "pure" or "pure looking.") This means that selection for breed type is especially important in grading up programs - although, even though such selection is important in any pure breeding population, it is frequently overlooked.

At higher levels of grade, which for my thinking certainly includes 31/32 or anything higher, the influence of outside genetic material is minimal. At this level, the animals are performing and breeding like most purebreds. These upgraded animals may have a slight advantage in overall vigor, and offer breeds enough fresh genetics to be a great boon to some of the very rare breeds. At the same time, these upgrades pose a minimal threat that any of the genetic uniqueness of the breed will be lost. This hearkens back to the principle that breeds are valuable because they are consistent and predictable. Any breeding practice that does not threaten the consistency and predictability of a breed does not threaten its status as a breed either, and that certainly includes grading up.

The careful reader has noticed that the preceding discussion designates the 7/8 grades as generally not sufficiently purebred, while the 31/32 grades are. This leaves in question the 15/16 animals, which are about 94 percent purebred. Breed associations will differ on whether these animals are sufficiently purebred or not, and the answer to this question has some legitimate leeway as different breeds are discussed. These 15/16 animals are generally "purebred enough" to be considered breed members, but in some breeds with reasonable levels of genetic diversity it may be wise to proceed to higher levels of grade before considering the graded animals purebred. It is important to remember, though, that if a very high level of grade is required (63/64 for example) the potential genetic benefits of grading up will be largely lost to the breed. Unfortunately, there is not a magic grade-up number we can designate to ensure breed conservation or breed vitality.

Breed purity, and grading up, have taken on some political overtones in many breeder circles. Breed purity is assumed by many to be absolute, inviolate, and ancient. The truth is, the origins of most breeds are fairly recent. Breed formation was simply a response to a need for predictable animals of a given type. Most origins were fairly broad, so that genetic viability was assured. As herd and flock books were closed and matings were only within the narrowly defined breed, the genetic character of breeds changed from somewhat open to absolutely closed. Some breeds are now suffering varying degrees of inbreeding depression from restrictive matings only within the purebred population.

Dairy goat breeding may illustrate some of these issues. Most dairy goat breeds include a purebred section, in which all matings are between members of the registered breed. Grading up is also allowed and results are documented in a section of the registry called "American." For example, a Nubian is a purebred Nubian; an American Nubian is a grade animal. Breed politics are such that grade goats do not meet with the market success of the purebreds. Many American goats, however, outperform their purebred counterparts, so those commercial producers may actually prefer the American counterpart to the purebred. In this situation, the safeguarding of the breed resource as a closed genetic pool has decreased its utility as a viable commercial entity‹ which is counter to the original aims of breed development!

While pure breeding and purebreds are important, the issue of grading up does need to be evaluated as to whether it has a place in breed maintenance, management, and conservation. If carefully managed and operated, grading up does not threaten the status of any breed as a genetic resource. This is at variance with the politics of many breeds, and so grading up is likely to remain rare.

With many international breeds, it is also important to fit policies and procedures into those accepted in other countries, and generally, the most restrictive country is going to call the shots on this issue. Eventually, all breeds are going to need to address the issue of grading up verses absolute breed closure.

The downside of completely closed populations is slowly being played out in breeds such as the Thoroughbred horse and in many dog breeds. This will give many people cause to evaluate what a breed is, why it is valuable, and how best to manage its genetic status.

Any grading up program must be carefully monitored to assure that appropriate levels of grade are achieved before inclusion into the purebred breed. At the same time it is important to recognize the value of grades to the viability and production of the breed. For a breed to fully reap the benefits of grading up (numerical expansion, increased market for breeding males, some gain in genetic vigor) the grade animals must be considered as full members of the breed, not second-class citizens. That is where breed politics come into the picture, and breed politics frequently do not have an answer in biology.

In the past, I considered that grading up had a legitimate and important role in some breeds (notably landraces or recently developed breeds) but had little, if any benefit to some older, long established breeds. After pondering the issue for many years I have switched my thinking somewhat, and believe graded up animals offer pure breeds a real opportunity for both vitality and viability.

Grading up allows breeds to avoid the problems of a tightly closed gene pool, and at the same time safeguards the genetic predictability of breeds. This is not one of the issues about which I generate huge amounts of passion since breeds have little to gain from grading up, but none has much, if anything, to lose. At the same time it has been interesting to observe my changed thinking on the subject. These thoughts are shared only to stimulate thinking and discussion. The final determination of the appropriateness of grading up for any breed is going to be determined by tricky issues such as breed politics and reciprocity between national herd books, which is an absolutely essential issue for international breeds. Grading up does, however, make good genetic sense for nearly every breed, and graded up animals should be included as full members of the breed.

D. Phillip Sponenberg, DVM, Ph.D. is Professor of Pathology and Genetics at Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, in Blacksburg, Virginia. He is a long-time member of ALBC, and serves as the Technical Coordinator on the ALBC staff. He can be reached via e-mail at dpsponen@mail.vt.edu.

As promised, here are some photos that illustrate what grading up looks like on our farm. This is Helen as a lamb, born in March of 2001. She is a half Bond half Corriedale ewe that carries (phenetypically, just from looking at her) white genes and spotting genes ... that's not dirt, its fawn-coloured ears and spots. As the moorit Bonds can ONLY contribute the most recessive brown moorit genes, we know that she also carries those genes. As it turns out, Helen doesn't look very much like a Bond, nor all that much like a Corriedale either. She is a good sized ewe, more like a Corriedale in frame structure, but definitely genetically got the Bond wool characteristics. Last Fall, she was bred to the other Bond ram and here is her lamb.

This is Helen's ewe lamb, Poppy. She is a 3/4 Bond and as luck would have it, she is also moorit ... the least likely colour outcome. Little Poppy also looks very much like a purebred Bond lamb looks in her character, but probably will be larger in frame. This is just a guess based on her birth weight, which was 11.5 pounds. While this is just about our flock birth weight average, it is larger than the birth weights of the twin purebred Bonds. What may be happening here on our farm, is that differences in feeding and management may show increases in time, of birth weights (of the Bonds) as well as frame size. The frame size increases may have more to do with the grading up?

This is Anneke, Kalmia's purebred Bond ewe lamb from this Spring. As a single, her birth weight was also more than would have been that of a twin. She has, as a purebred, all of the character of the Bonds as well as the moorit colour. Not all of the half Bond / half Corriedale ewes produced moorit lambs. We also got 3/4 Bond white lambs as well as 3/4 black (or very dark brown) lambs. We have found that these dark brown lambs become a very light grey/silver, almost taupe colour.

This is Diana and her twin moorit 3/4 Bond lambs. They also look very much like the Bonds, except for having a larger birth weight, even for twins. They also weighed 11 and 11.5 pounds. We are very pleased with this year's lamb crop and hope that the rains continue on into the Spring. They say it will take another 3 years of normal moisture to recover from the drought. We need the grass to grow and feed all of these new lambs!

[an error occurred while processing this directive]