By Carol Beuchat PhD
There are lots of questions about cross breeding, and the problem in the dog fancy is that there is precious little data to address them. In the absence of data, discussions consist of opinions and assumptions, along with a fair amount of fear around the thought that a breed could be ruined or even lost due to cross breeding.
First of all, no breed will be lost due to cross breeding. In fact, the major obstacle to restoring genetic diversity to breeds is getting the introduced genetic material distributed through the breed. Genetic diversity can't spread like a virus. It must be deliberately transmitted by breeding. With many thousands of dogs scattered worldwide, and with inbreeding levels in many breeds through the roof, it will take a mighty effort involving many, many breeders and lots of planning by scientists to make a significant difference in the gene pool of a breed. And of course, it's quite easy to "protect" dogs from the introduced genetics; just don't breed to them or their descendants. So, fear or ruining a breed is unfounded and can be crossed off the list of things to worry about.
Next, we need to consider the genetic situation of purebred dogs. It's not the case that contininuing to breed in the existing (closed) gene pool is "protecting" the breed. The fact that this results in a steady deterioriation in health and fitness (reproduction, survival, etc) should be clear enough evidence that something critical to the essence of the breed is being systematically lost over the generations and genetics explains why. Healthy animal populations have very low levels of inbreeding. Inbreeding causes homozygosity, which replaces two different alleles with two copies of the same one. If the lost allele was functional, some genetic information is lost along with it. Every breeding to a related dog produces more homozygosity, and more alleles are lost, so while the downward trajectory might not be readily noticible over the short term, it does become apparent sooner or later. Increasing homozygosity cannot produce better dogs. It simply can't. So continuing to practice inbreeding as we have for decades is making a choice to do something that is harmful both to individuals and the breed.
First of all, no breed will be lost due to cross breeding. In fact, the major obstacle to restoring genetic diversity to breeds is getting the introduced genetic material distributed through the breed. Genetic diversity can't spread like a virus. It must be deliberately transmitted by breeding. With many thousands of dogs scattered worldwide, and with inbreeding levels in many breeds through the roof, it will take a mighty effort involving many, many breeders and lots of planning by scientists to make a significant difference in the gene pool of a breed. And of course, it's quite easy to "protect" dogs from the introduced genetics; just don't breed to them or their descendants. So, fear or ruining a breed is unfounded and can be crossed off the list of things to worry about.
Next, we need to consider the genetic situation of purebred dogs. It's not the case that contininuing to breed in the existing (closed) gene pool is "protecting" the breed. The fact that this results in a steady deterioriation in health and fitness (reproduction, survival, etc) should be clear enough evidence that something critical to the essence of the breed is being systematically lost over the generations and genetics explains why. Healthy animal populations have very low levels of inbreeding. Inbreeding causes homozygosity, which replaces two different alleles with two copies of the same one. If the lost allele was functional, some genetic information is lost along with it. Every breeding to a related dog produces more homozygosity, and more alleles are lost, so while the downward trajectory might not be readily noticible over the short term, it does become apparent sooner or later. Increasing homozygosity cannot produce better dogs. It simply can't. So continuing to practice inbreeding as we have for decades is making a choice to do something that is harmful both to individuals and the breed.
| Inevitably, the liveliest arguments are about what dogs to cross to. Because dog breeders have not historically done much organized cross breeding, they fall back on what they know (or believe) about breeding purebred dogs. But the purpose of purebred dog breeding is very different than that for cross breeding. It would be quite a surprise if the same procedures suited both. This isn't the place for a long discussion about selecting breeds for crossing. But I will make a few comments that will encourage you to think differently about selecting breed crosses. |  |
We have an exestential crisis in purebred dogs. Levels of inbreeding are - in a biological sense - stratospheric. They are highly detrimental to health. They are driving breeds to extinction. We risk losing breeds entirely if we don't fix this. In this situation, there should be only one consideration when selecting a breed to cross to - what animals will introduce the highest possible amount of diversity? For this, you want the lowest possible level of inbreeding in the animals used for crossing. This is because homozygous loci, with two copies of the same allele, will pass on the same allele to all offspring, when our goal is to increase alleleic diversity. So crossing to another purebred (inbred) dog breed is usually not the best option unless there are individuals with exceptionally low levels of inbreeding.
As for crossing with closely related breeds- We know that related breeds usually share some genetics, so this has the same problem as crossing to any relative - it might result in unintended homozygosity. Finally, because cross breeding is a project with a very specific purpose, it is critical that the dogs selected for the project will in fact address the problem you are trying to solve. Compromising on improving genetic diversity because you're worried about temperament or coat color is definitely not what you want to do if the future of a breed hangs in the balance. These are issues that can be address with selective breeding. For this reason, the dogs to cross to should be determined by carefully identifying the problems to be addressed and examining the genetics of the potential crossing breed to make certain those issues will be solved. For this reason, the selection of dogs to cross to will be one of the last decisions you make.
It's great that breeders are thinking more and more about the need for cross breeding and how to go about it. But recognize that to get this right, you will need to base decision-making on facts and expertise that dog breeders don't have. Certainly, opinions and assumptions have no value at all, because they are more likely to be detrimental than helpful given the different goals of purebred and crossbred breeding.
I have been thinking about these issues for a long time, and we seem finally to be at a tipping point where ideas are developing into action. It's a critical time for breeders to have access to expertise and guidance, and for the most part the kennel clubs lack both for the same reasons the breeders do. A couple of kennel clubs have professional population geneticists on board now that do have relevant expertise. But the seriousness of the inbreeding problem and the hundreds of breeds that need immediate attention dwarf the amount of attention and effort a single individual can invest in planning and executing effective projects to restore genetic health to dog breeds. I personally think we need to create a "center of expertise" of some sort that will provide the resources we will need to tackle the huge project of restoring dog breeds to health. I've been thinking about how to do this for a long time (years), and the essential needs are money and a significant number of breeders that will be committed to initiating and participating in restoration projects that will be complex and take years.
Finally, there is a huge need for education. I said at the top that absence of facts results in decision-making based on opinions and fear, which is more likely to result in failure than not. Breeders are not well-versed in the biology and genetics of animal breeding (cross-breeding or otherwise), and there needs to be a big push to remedy this. The immediate advantage will be having discussions about topics like the one for this post that can be based on facts and actual information, instead of speculation couched in fear. Everybody wants to breed better dogs. Will education help? Absolutely.
Keep talking about cross breeding. But replace fear and opinions with facts and data. And stifle the urge to just do something yourself. Crossbreeding projects will necessarily be team efforts. Seek out the professional expertise that can guide crossing programs to success.
As for crossing with closely related breeds- We know that related breeds usually share some genetics, so this has the same problem as crossing to any relative - it might result in unintended homozygosity. Finally, because cross breeding is a project with a very specific purpose, it is critical that the dogs selected for the project will in fact address the problem you are trying to solve. Compromising on improving genetic diversity because you're worried about temperament or coat color is definitely not what you want to do if the future of a breed hangs in the balance. These are issues that can be address with selective breeding. For this reason, the dogs to cross to should be determined by carefully identifying the problems to be addressed and examining the genetics of the potential crossing breed to make certain those issues will be solved. For this reason, the selection of dogs to cross to will be one of the last decisions you make.
It's great that breeders are thinking more and more about the need for cross breeding and how to go about it. But recognize that to get this right, you will need to base decision-making on facts and expertise that dog breeders don't have. Certainly, opinions and assumptions have no value at all, because they are more likely to be detrimental than helpful given the different goals of purebred and crossbred breeding.
I have been thinking about these issues for a long time, and we seem finally to be at a tipping point where ideas are developing into action. It's a critical time for breeders to have access to expertise and guidance, and for the most part the kennel clubs lack both for the same reasons the breeders do. A couple of kennel clubs have professional population geneticists on board now that do have relevant expertise. But the seriousness of the inbreeding problem and the hundreds of breeds that need immediate attention dwarf the amount of attention and effort a single individual can invest in planning and executing effective projects to restore genetic health to dog breeds. I personally think we need to create a "center of expertise" of some sort that will provide the resources we will need to tackle the huge project of restoring dog breeds to health. I've been thinking about how to do this for a long time (years), and the essential needs are money and a significant number of breeders that will be committed to initiating and participating in restoration projects that will be complex and take years.
Finally, there is a huge need for education. I said at the top that absence of facts results in decision-making based on opinions and fear, which is more likely to result in failure than not. Breeders are not well-versed in the biology and genetics of animal breeding (cross-breeding or otherwise), and there needs to be a big push to remedy this. The immediate advantage will be having discussions about topics like the one for this post that can be based on facts and actual information, instead of speculation couched in fear. Everybody wants to breed better dogs. Will education help? Absolutely.
Keep talking about cross breeding. But replace fear and opinions with facts and data. And stifle the urge to just do something yourself. Crossbreeding projects will necessarily be team efforts. Seek out the professional expertise that can guide crossing programs to success.
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Visit our Facebook Groups
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...the latest canine news and research
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...the science of animal breeding
