Sponenberg: Grading Up = Important Preservation Tool
Jul 4, 2015 14:14:57 GMT -5
Olga, kansasdexters, and 3 more like this
Post by Cascade Meadows Farm - Kirk on Jul 4, 2015 14:14:57 GMT -5
by Phil Sponenberg
"Grading up is an interesting and useful process for animal breeders. It is often seen as a threat to purebred stock, when in fact it is one sure way to ensure breed survivability over long centuries of purebred breeding. Understanding what upgrading is and how it affects a breed genetically are extremely important issues of breeders of all purebred breeds.
Grading up is the sequential use of purebred 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 sire of the breed, providing offspring that are 3/4 the pure breed. The next generation provides offspring that are 7/8, the next is 15/16, then 31/32, 63/64, and then 127/128 and so on.
While upgrading usually involves the use of purebred sires on grade dams, it is biologically valid to also use purebred dams for this process. It is also worth pondering that due to the unique genetic contributions of females (mitochondria, for example) it may actually be best for upgrading programs to insist on the use of both purebred males and purebred females in some of the generations to assure that breed-appropriate genetic material that is sex specific (Y chromosomes, mitochondria) have come from the purebred pool.
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 (generally) for crossbreeding.
Grading up has lots of positives, a few negatives, and has 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. Breeds are useful because they are reasonably consistent genetic packages. That is, they have certain combinations of genes that are repeated throughout the breed, and this consistent genetic makeup makes breeds reasonably predictable. It is the predictability that is the key to the value of breeds, for without predictability it is impossible to match breed to place, purpose, and system. So, anything that conserves the aspect of breeds as consistent genetic packages tends to be helpful, and likewise anything that detracts from it is deterimental.
The key to understanding upgraded animals is that each of them does indeed have at least the potential for some genetic material that is not in the original pure breed. How much, and what this means as a practical issue, is important. Grades usually begin to very closely resemble the purebreed 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, and individual animals could be found that are either a lot more or a lot less “pure” or “pure looking”. What this means is that selection towards breed type is especially important in upgrading programs - although such selection is important in any purebreeding population and 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, and the animals are performing and breeding like most purebreds. These upgraded animals may have a slight advantage in overall vigor, and in fact do offer breeds enough of a breath of fresh air (or fresh genetics) that can be a great boon to some very rare breeds, while at the same time posing 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, and that certainly includes upgrading.
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% 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 considered. 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 wiser to proceed to higher levels of grade before considering the graded animals as purebred. It is important to remember, though, that if a very high level of grade is required (63/64 for example) then the potential genetic benefits of upgrading will be largely lost to the breed. There is not single magic cutoff point for level of grade needed for breed conservation as well as breed vitality.
Breed purity, and upgrading, have taken on some political overtones in many breed circles. Breed purity is assumed by many to be absolute, inviolate, and ancient. The truth is more that the origins of most breeds are fairly recent, and 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 somewhat from somewhat open to absolutely closed. Some breeds are now suffering varying degrees of depression (inbreeding depression) from being locked down tight with 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. Upgrading is also allowed, and results in the designation “American”, so that a Nubian (or Alpine, or Toggenburg) is a purebred Nubian (or other breed), an American Nubian is an upgrade. Breed politics are such that upgraded goats do not meet with the market success of the purebreds. Many American goats, though, outperform their purebred counterparts, so that several commercial producers 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!
So while purebreeding and purebreds are important, the issue of upgrading does need to be evaluated as to whether it has a place in breed maintenance, management, and conservation. If carefully managed and operated, upgrading does not threaten the status of any breed as a genetic resource. This is at variance with the politics of many breeds, and so upgrading 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. All breeds are going to eventually need to address the issue of upgrading versus absolute breed closure. The downside of completely closed populations is slowly being played out in breeds such as the Thoroughbred and 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.
Grading up, if carefully managed and monitored, can assure that purebreeds remain viable and vital, and also can assure that they retain their status as genetic resources. Any upgrading program must be carefully monitored to assure that appropriate levels of grade are achieved before inclusion of animals into the purebred breed. At the same time it is important for breeds to recognize the value of grades to the viability and production of the breed. This is somewhat negated by the political situation in many breeds where the upgraded animals are generally considered second-class citizens. For a breed to fully reap the benefits of upgrading (numerical expansion, increased market for breeding males, some gain in genetic vigor) the upgraded animals must indeed be considered as full members of the breed. That is where breed politics get into the picture, and breed politics frequently do not have an answer in biology.
In the past I considered that upgrading 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 realize graded-up animals offer purebreeds a real opportunity for vitality and viability. Grading up allows breeds to avoid the problems of a tightly shut gene pool, while at the same time safeguarding the status of breeds as predictable genetic packages. This is not one of the issues about which I generate huge amounts of passion (some breeds have little to gain from upgrading, but none has much if anything to lose), but it has been interesting for me to watch my thinking change on the subject. These thoughts are shared only to stimulate thinking and discussion. The final determination of the appropriateness of upgrading for any breed is going to be determined by tricky issues such as breed politics, and reciprocity between national herdbooks which is an absolutely essential issue for international breeds. Upgrading does, however, make good genetic sense for nearly every breed, and upgraded animals should be included as full members of the breed."
www.oocities.org/horsesnewmexcom/gradingup.htm
"Grading up is an interesting and useful process for animal breeders. It is often seen as a threat to purebred stock, when in fact it is one sure way to ensure breed survivability over long centuries of purebred breeding. Understanding what upgrading is and how it affects a breed genetically are extremely important issues of breeders of all purebred breeds.
Grading up is the sequential use of purebred 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 sire of the breed, providing offspring that are 3/4 the pure breed. The next generation provides offspring that are 7/8, the next is 15/16, then 31/32, 63/64, and then 127/128 and so on.
While upgrading usually involves the use of purebred sires on grade dams, it is biologically valid to also use purebred dams for this process. It is also worth pondering that due to the unique genetic contributions of females (mitochondria, for example) it may actually be best for upgrading programs to insist on the use of both purebred males and purebred females in some of the generations to assure that breed-appropriate genetic material that is sex specific (Y chromosomes, mitochondria) have come from the purebred pool.
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 (generally) for crossbreeding.
Grading up has lots of positives, a few negatives, and has 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. Breeds are useful because they are reasonably consistent genetic packages. That is, they have certain combinations of genes that are repeated throughout the breed, and this consistent genetic makeup makes breeds reasonably predictable. It is the predictability that is the key to the value of breeds, for without predictability it is impossible to match breed to place, purpose, and system. So, anything that conserves the aspect of breeds as consistent genetic packages tends to be helpful, and likewise anything that detracts from it is deterimental.
The key to understanding upgraded animals is that each of them does indeed have at least the potential for some genetic material that is not in the original pure breed. How much, and what this means as a practical issue, is important. Grades usually begin to very closely resemble the purebreed 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, and individual animals could be found that are either a lot more or a lot less “pure” or “pure looking”. What this means is that selection towards breed type is especially important in upgrading programs - although such selection is important in any purebreeding population and 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, and the animals are performing and breeding like most purebreds. These upgraded animals may have a slight advantage in overall vigor, and in fact do offer breeds enough of a breath of fresh air (or fresh genetics) that can be a great boon to some very rare breeds, while at the same time posing 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, and that certainly includes upgrading.
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% 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 considered. 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 wiser to proceed to higher levels of grade before considering the graded animals as purebred. It is important to remember, though, that if a very high level of grade is required (63/64 for example) then the potential genetic benefits of upgrading will be largely lost to the breed. There is not single magic cutoff point for level of grade needed for breed conservation as well as breed vitality.
Breed purity, and upgrading, have taken on some political overtones in many breed circles. Breed purity is assumed by many to be absolute, inviolate, and ancient. The truth is more that the origins of most breeds are fairly recent, and 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 somewhat from somewhat open to absolutely closed. Some breeds are now suffering varying degrees of depression (inbreeding depression) from being locked down tight with 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. Upgrading is also allowed, and results in the designation “American”, so that a Nubian (or Alpine, or Toggenburg) is a purebred Nubian (or other breed), an American Nubian is an upgrade. Breed politics are such that upgraded goats do not meet with the market success of the purebreds. Many American goats, though, outperform their purebred counterparts, so that several commercial producers 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!
So while purebreeding and purebreds are important, the issue of upgrading does need to be evaluated as to whether it has a place in breed maintenance, management, and conservation. If carefully managed and operated, upgrading does not threaten the status of any breed as a genetic resource. This is at variance with the politics of many breeds, and so upgrading 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. All breeds are going to eventually need to address the issue of upgrading versus absolute breed closure. The downside of completely closed populations is slowly being played out in breeds such as the Thoroughbred and 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.
Grading up, if carefully managed and monitored, can assure that purebreeds remain viable and vital, and also can assure that they retain their status as genetic resources. Any upgrading program must be carefully monitored to assure that appropriate levels of grade are achieved before inclusion of animals into the purebred breed. At the same time it is important for breeds to recognize the value of grades to the viability and production of the breed. This is somewhat negated by the political situation in many breeds where the upgraded animals are generally considered second-class citizens. For a breed to fully reap the benefits of upgrading (numerical expansion, increased market for breeding males, some gain in genetic vigor) the upgraded animals must indeed be considered as full members of the breed. That is where breed politics get into the picture, and breed politics frequently do not have an answer in biology.
In the past I considered that upgrading 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 realize graded-up animals offer purebreeds a real opportunity for vitality and viability. Grading up allows breeds to avoid the problems of a tightly shut gene pool, while at the same time safeguarding the status of breeds as predictable genetic packages. This is not one of the issues about which I generate huge amounts of passion (some breeds have little to gain from upgrading, but none has much if anything to lose), but it has been interesting for me to watch my thinking change on the subject. These thoughts are shared only to stimulate thinking and discussion. The final determination of the appropriateness of upgrading for any breed is going to be determined by tricky issues such as breed politics, and reciprocity between national herdbooks which is an absolutely essential issue for international breeds. Upgrading does, however, make good genetic sense for nearly every breed, and upgraded animals should be included as full members of the breed."
www.oocities.org/horsesnewmexcom/gradingup.htm
It would take a LOT of education to change perceptions. cheers, carol davidson