RECOMMENDED READING for FUTURE HAVANESE PUPPY OWNERS
Inbreeding in Dogs – Problems, Benefits and Reasons, Retrieved June 2, 2016
From: Inbreeding in Dogs – Problems, Benefits and Reasons
Disadvantages of inbreeding dogs
While inbreeding to some extent has played a part in the establishment of all modern breeds of dog and will likely continue to do so, inbreeding also has a significant amount of potential problems and risk factors associated with it.
Inbreeding results in an increased likelihood of undesirable traits being inherited into the subsequent offspring, and heightens the chances of recessive mutations occurring. While sometimes these mutations are a desirable effect of selective breeding, such as in the case of the shar-pei as mentioned above, the potential for undesirable and unforeseen mutations occurring alongside of these is considerably greater. Several hereditary conditions and illnesses which can be inherited by dogs only occur if the pups inherit the recessive gene from both their sire and dam, and the likelihood of them having two parents with the recessive gene which then causes the potential problem in the pup is of course much higher if the two parents are closely related in the first place.
Conditions such as hip dysplasia and patella luxation are just two of the many potential congenital defects and hereditary conditions that can occur from inbreeding, which leads to all of the pedigree dogs of a given breed being genetically relatively closely related.
Out crossing to unrelated dogs is also very likely to occur, and while this has many benefits that inbreeding does not have such as reduced likelihood of inherited flaws and genetic mutations developing, it also serves to potentially dilute out the desirable traits of the original dogs, and so a balance between the two factors must be reached.
Potential Health Defects in Pedigreed Dogs, Insurance and Checking the Pedigree
As well as of course the problems of potential genetic health defects presenting themselves in later life if you buy a pedigree pup of a higher risk breed, insurance for pedigree dogs is generally rather higher than for mixed breeds, and significantly so in the case of well known selectively bred dogs such as the bulldog and pug. Due to the elevated risk factors associated with insuring breeds like these, insurance can prove to be very costly, and even then, sometimes insurance will not cover certain congenital and hereditary diseases and conditions due to their high level of prevalence within the breed.
If you are considering buying a pedigree dog, it's important to check out its history first and learn about any potential hereditary risk factors, to make sure that the dog you buy is healthy, and that you are not storing up problems for yourself and your dog later down the line.
Hartwell, S. (1996). Pros and Cons of Inbreeding. Retrieved June 27/2016
From: Implications of Inbreeding for the Dog Breeder
Most dog breeders are well aware of potential pitfalls associated with inbreeding although it is tempting for a novice to continue to use one or two closely related lines in order to preserve or improve type.
Breeding to an unrelated line of the same breed (where possible) or outcrossing to another breed (where permissible) can ensure vigor. Despite the risk of importing a few undesirable traits which may take a while to breed out, outcrossing can prevent a breed from stagnating by introducing fresh genes into the gene pool. It is important to outcross to a variety of different dogs considered to be genetically "sound" (do any of their previous offspring exhibit undesirable traits?) and preferably not closely related to each other.
How can you tell if a breed or line is becoming too closely inbred? One sign is that of reduced fertility in either males or females. Male dogs are known to have a low fertility rate. Small litter sizes and high puppy mortality on a regular basis indicates that the dogs may be becoming too closely related. The loss of a large proportion of dogs to one disease indicates that the dogs are losing/have lost immune system diversity. If 50% of individuals in a breeding program die of a simple infection, there is cause for concern.
Highly inbred dogs also display abnormalities on a regular basis as "bad" genes become more widespread. These abnormalities can be simple undesirable characteristics such as misaligned jaws (poor bite) or more serious deformities. Sometimes a fault can be traced to a single male or female that should be removed from the breeding program even if it does exhibit exceptional type. If its previous progeny are already breeding it's tempting to think "Pandora's Box is already open and the damage done so I'll turn a blind eye." Ignoring the fault and continuing to breed from the dog will cause the faulty genes to become even more widespread in the breed, causing problems later on if its descendants are bred together.
The Kennel Club – Breeding for Health – inbreeding retrieved on June 27/20116 @ http://www.thekennelclub.org.uk/health/breeding-for-health/inbreeding/
From: Breeding for Health
How can you measure the degree of inbreeding? The degree of inbreeding can be measured by using an Inbreeding Coefficient, or Coefficient of Inbreeding (COI). This is the probability that two copies of the same gene have been inherited from an ancestor common to both the sire and dam. The lower the degree of inbreeding, the lower the inbreeding coefficient.
Putting your COI result into perspective
The COI calculator provides you with a percentage score; the lower the percentage, the lower the degree of inbreeding.
Therefore, an inbreeding coefficient of:
0% indicates a dog that comes from two unrelated parents, based on all available pedigree information
12.5% would equate to the genetic equivalent of a dog produced from a grandfather to granddaughter mating
25% would equate to the genetic equivalent of a dog produced from a father to daughter mating.
Inbreeding can be accumulative, so if it has occurred to a significant degree over several generations, the inbreeding coefficient may exceed 25%.
Using the COI to help make breeding decisions
Breeders should be aware that the inbreeding coefficient is a measurement of risk and does not guarantee that puppies produced will, or will not, have any inherited health conditions. There are other equally important factors to consider when deciding whether two dogs should be mated together, such as temperament, available health test results, the general health of the dogs etc. Your decision should be well balanced between the inbreeding coefficient and the good qualities of the sire/dam that you are considering.
Beuchat, C. PhD (6/4/2015) COI FAQS: Understanding the Coefficient of Inbreeding Retreived on June 17/2016
The deleterious effects of inbreeding begin to become evident at a COI of about 5%. At a COI of 10%, there is significant loss of vitality in the offspring as well as an increase in the expression of deleterious recessive mutations. The combined effects of these make 10% the threshold of the "extinction vortex" - the level of inbreeding at which smaller litters, higher mortality, and expression of genetic defects have a negative effect on the size of the population, and as the population gets smaller the rate of inbreeding goes up, resulting in a negative feedback loop that eventually drives a population to extinction.
So, in terms of health, a COI less than 5% is definitely best. Above that, there are detrimental effects and risks, and the breeder needs to weigh these against whatever benefit is expected to gained. Inbreeding levels of 5-10% will have modest detrimental effects on the offspring. Inbreeding levels above 10% will have significant effects not just on the quality of the offspring, but there will also be detrimental effects on the breed.
For comparison, mating of first cousins produces a COI of 6.25%; in many societies this is considered incest and is forbidden by law). Mating of half-siblings produces a COI of 12.5%; mating of full siblings produces a COI of 25%
Do I still have to worry about COI if I am doing the health tests for my breed?
YES. For genetic disorders caused by a single recessive mutation, the DNA test will prevent the 1-in-4 risk of producing an affected animal by crossing two carriers. So, that test eliminates a risk of 25% for the disorder caused by that mutation.
But every dog has many mutations, and you have no way to know about them if a dog has only one copy and they are not expressed. If you breed two dogs with some of the same mutations, you can expect that the offspring will be homozygous for 25% of them. Many of these mutations might only have very slight effects that you wouldn't notice as a "disease", but it is the accumulation of these small effects that causes the loss of vigor and vitality in inbred animals that is called "inbreeding depression". DNA tests tell you only about one particular gene, a known risk. But if the COI of a litter is 25%, you can expect that 25% of the deleterious mutations in each puppy will be expressed.
To breed healthy animals, you need to worry about ALL of the potential risks, and the one thing we can be sure of is that there are many more recessive mutations than the ones we have DNA tests for. Why would you invest in the DNA tests available for your breed, then produce a litter in which 15%, or 25%, or 40% of the other mutations in every animal will be expressed?
You must remember that the coefficient of inbreeding is not a measure of health. It is a measure of RISK, and with or without DNA tests, it is the best way to judge the level of genetic risk you are taking when you breed a litter.
MORE ARTICLES TO READ
Bateson, P. (2010). Independent Inquiry into Dog Breeding. Micropress Ltd., Halesworth, Suffolk
Beuchat, Carol, PhD. (1/27/2016). Three Key Strategies to Reduce Genetic Disorders in Dogs
Blog The Institute of Canine Biology. Retrieved on May 22, 2016 @ http://www.instituteofcaninebiology.org/blog/why-all-the-fuss-about-inbreeding-or-why-do-we-have-so-many-genetic-disorders-in-dogs
Lanting, F Breeder/Buyer Relationship - Guarantees and Ethics by @ Lanting, F. THE BREEDER/BUYER RELATIONSHIP: GUARANTEES AND ETHICS. Retrieved on May 18/2016 @ http://www.dogstuff.info/breeder_buyer_relationship.html
Thorpe-Vargas, S. Ph.D. Genetics And Breeding Strategies: Essays For The Dog Breeder
Reprinted with permission Retrieved on May 22, 2016 @ https://pawpeds.com/pawacademy/genetics/breedingstrategies/chapter4.html
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