Should We Breed With Carriers?

By Cathryn Mellersh, Animal Health Trust, November 2011

carrier‘ is the term given to an individual (of any species) that carries a single copy of a recessive mutation that is associated with a specific inherited condition, usually an inherited disorder. An individual will only suffer from a recessive disorder if in inherits two copies of the causal mutation, one from each parent. If it inherits a single copy of the mutation it will remain healthy but will pass the mutation on to about half of its offspring.

Breeding with Carriers
Once a specific disease mutation has been identified a DNA test can be developed that enables the identification of non-symptomatic carriers. Knowing which dogs carry the mutation and which don’t (the so-called ‘clear’ dogs) enables breeders to make sensible choices about the dogs they mate together. All dogs can be safely bred with provided at least one of the mating pair is clear of the mutation (see Table below). Breeding dogs that will never develop the condition should obviously be the priority for all conscientious breeders and the desire to eliminate a disease-associated mutation from a breed should therefore be the long-term goal. But the instinct to choose only clear dogs to breed from, as soon as a DNA test becomes available, may not always be a sensible choice and the rest of this document discusses why.

If carriers are prevented from breeding the opportunity to pass the rest of their genetic material to the next generation is also lost and the genetic diversity of the remaining population is thus reduced. It is worth remembering that there is a clear and well-established link between the genetic diversity of a population and its overall health, and that breeding closely related individuals tends to lead to the accumulation of deleterious recessive mutations in the population. This is due to the fact that an individual is more likely to inherit two identical copies of a mutation if its parents share common ancestors than if they are unrelated, and the more com man ancestors the parents share the greater that chance is.

It is also worth remembering that the disease mutation for which there is a DNA test is not the only mutation a carrier has. Every human, on average, carries about 50 recessive mutations and there is no reason to believe the average dog won’t carry a similar number. So the only real difference between a clear and a carrier is the single mutation that can be tested for. Both dogs will both carry around 49 other mutations that the breeder doesn’t know about and can’t test for. If carriers are not bred from and clear dogs are used extensively then there is a real risk that other mutations will increase in frequency in the breed and new inherited disease(s) could emerge.

There is no reason why the eventual elimination of a disease mutation from a breed shouldn’t be the goal, once a DNA test for that mutation becomes available. But, providing all breeding dogs are tested for the mutation prior to mating, the breeders can take their time and ensure that desirable traits are not eliminated along with the disease mutation and that the genetic diversity of the breed is not reduced.

Mutation Frequency
The speed with which the mutation can be eliminated depends on several factors, including the frequency of the mutation, the population structure and the rate of inbreeding for that breed. The more frequent the mutation is the more slowly it should be eliminated. Calculating the true frequency of a mutation is not trivial, and requires a random subset of a breed be screened. Dogs that are tested once a commercial DNA test becomes available are not always representative of the breed as a whole, and similar1y cohorts of dogs that have been sampled by a research institute during development of the DNA test are also rarely characteristic of the breed.

The frequency of a mutation is typically expressed as the fraction of chromosomes in a population that carry the mutation. For example, if the frequency of a mutation is described as 0.1, this means that 10% of the chromosomes in that breed carry the mutation and the remaining 90% carry the normal copy of DNA. If 10% of the chromosomes carry the mutation then just under 20% of dogs are expected to be carriers and about 1 % of dogs will be affected.

Breeding Advice
Carriers should always be included in the first one to two generations that follow the launch of a DNA test for a recessive mutation, regardless of the frequency of the mutation, to give breeders the opportunity to capture desirable traits, such as breed type and temperament, before they start to select for dogs that are clear of the mutation. Specific breeding policy for future generations should be breed-dependent and ideally formulated after consideration of factors such as the population structure and rate of inbreeding. But in general terms, carriers should only be removed from the breeding population if the frequency of the mutation is below 0.01 (1 %), as this will mean only around 2% of dogs will be prevented from breeding. Avoiding carriers of a mutation that is more frequent will result in a greater number of dogs being prevented from breeding and could lead to a detrimental loss of diversity for the breed.

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Genetic Testing and Genetic Counseling in Pet and Breeding Animals

by Jerold S. Bell, DVM, Tufts University School of Veterinary Medicine  Jerold.Bell@tufts.edu

Genetic testing and genetic counseling are not just for breeding animals. They include; testing for the bleeding disorder von Willebrand’s disease before performing surgery on susceptible breeds, altering diets for pets that are prone to developing bladder stones or crystals, and switching from rapid growth puppy food to lower calorie foods in young, large breed dogs, so that joint tissues can develop at a more uniform rate.

The hallmark of genetic disease is the ability to predict disease before its onset. This allows the possibility of medical or surgical intervention in order to prevent later suffering. Knowledge of breed-related genetic disease and the tests that are available permit early diagnosis and treatment.

Breeders and veterinarians have been utilizing genetic tests since the beginning of domestic animal breeding. Most genetic tests measure the phenotype of an animal, or what you can see. These include radiographs, blood values, eye examinations, skin biopsies, urinalysis for crystals or metabolites, observations on structure or behavior, and ausculting for heart murmurs. Most tests of the phenotype only identify affected individuals, and not carriers. These may, or may not directly relate to the genotype, or the genes regulating the defect.

A test of the genotype is one that assesses the DNA of the animal. These tests can be run at any age, regardless of the age of onset of the disorder. Utilizing polymerase chain reaction (PCR) technology, affected, carrier, and normal individuals can be identified. As the majority of genetic disorders are recessive or have a major recessive component, the identification of carriers is important for effective management.

As additional DNA tests are developed for disorders, the role of genetic counseling becomes more important. Without these tests, the number of individuals that can be identified as carriers is low, even though many may be suspect due to having affected relatives. Breeds have closed gene pools; in other words, the diversity of genes in a given breed is fixed. The number of individuals removed from consideration for breeding based on concerns regarding a specific genetic disease is usually low. While this has slowed the management of genetic disease, it has also prevented genetic drift and diversity problems for pure breeds.

History has shown that breeders can be successful in reducing breed-wide genetic disease through testing and making informed breeding choices. However, there are also examples of breeds that have actually experienced more problems as a result of unwarranted culling and restriction of their gene pools. These problems include: reducing the incidence of one disease and increasing the incidence of another by repeated use of males known to be clear of the gene that causes the first condition, creating bottlenecks and  diminishing  diversity by eliminating all carriers of a gene from the

breeding pool, instead of breeding and replacing them, and concentrating on the presence or absence of a single gene and not the quality of the whole animal.

DNA tests have to be developed specifically for each breed (or group of related breeds that share an ancestral mutation). There are two different types of tests of the genotype; direct gene tests and linkage-based tests. Direct gene tests check for a specific mutation in a defective gene.  The animal either carries the defective gene, or does not.

Linkage-based DNA tests can be developed even if the defective gene causing a disorder has not been identified. Genome research has identified thousands of genetic markers, or “marker-DNA” that are spread across the chromosomes of the species. A linked-marker is a piece of DNA that lies close to the defective gene on a chromosome.

Breeders can use linkage-based genetic tests the same way direct genetic tests are used. The only difference is that you are not directly testing for the defective gene, only an associated marker; so false-positive and false-negative test results can occur.

A genetic crossover between paired chromosomes mixes the genes that an individual receives from its sire and dam. This occurs on a regular basis during the formation of eggs and sperm. As a defective gene and the linked marker are different areas of DNA that lie close together on a chromosome, it is possible that a genetic crossover can occur between them. This would separate the marker from the defective gene and create false positive (testing for the marker without the defective gene), or false negative (testing as normal, but having the defective gene) results. Depending on the relative distance between the marker and the defective gene on the chromosome, researchers can predict the frequency of false results for a linkage-based test; for example: 1 in 100.

If an individual’s linkage-based test for the defective gene is producing false-positive or false-negative results, all of its descendants that inherit this portion of the chromosome will also have false test results. This has been documented with families of Bedlington Terriers tested for the autosomal recessive copper toxicosis gene.

It is obvious that direct gene tests are better than linkage-based tests. However, a test with 90% or 95% confidence is better than no test at all. As genomic research progresses, researchers can identify the defective genes responsible for disorders, and can develop direct gene tests to replace linkage-based tests. The defective gene for copper toxicosis in the Bedlington Terrier has now been identified, and a direct gene test is now possible.

Based on the mode of inheritance of a disorder, and the availability of genotypic or phenotypic genetic tests, breeding management recommendations can be used to prevent or reduce the frequency of carrier or affected offspring. See the article “Breeding Strategies for the Management of Genetic Disorders” in the proceedings for specific recommendations.
Once a genetic test is developed, it allows breeders to positively determine if an individual is a carrier of a defective gene. The typical response of a breeder on finding that their animal is a carrier is to remove it from a breeding program. If a majority of breeders do this, it puts the breed’s gene pool through a genetic bottleneck that can significantly limit the diversity of the breed. The goal of genetic testing is to allow the superior genes of a breeding individual to be propagated, even if the animal is a carrier. One defective gene that can be identified through a genetic test, out of tens of thousands of genes is not a reason to stop breeding. If an owner would breed an individual if it tested normal for a genetic disease, then a carrier result should not change that decision.

Owners of carrier animals who are of breeding quality in other health, temperament, performance and conformation aspects should be bred to normal testing mates. This prevents the production of affected offspring. The breeder should be counseled to test the offspring prior to placement; to determine whether a pet or breeding home is appropriate. The goal is to replace the carrier parent with a quality, normal testing offspring that carries on the lineage of the breeding program.

If the only quality offspring is also a carrier, then breeders can use that offspring to replace the original carrier. The breeder has improved the quality of the breeding stock, even though the defective gene remains in the next generation. The health of the breed does depend on diminishing the carrier frequency and not increasing it. Breeders should therefore limit the number of carrier-testing offspring placed in breeding homes. It is important to carry on lines. A test that should be used to help maintain breed diversity should not result in limiting it.

By breeding and not selecting against carriers, breeders are selecting for a carrier frequency of fifty-percent; higher than most breed averages. Each breeder must assess the frequency of the defective gene in their own breeding stock and determine their own rate of progress. As each breeder reduces the number of carrier breeding stock, the frequency of the defective gene for the breed will decrease.

We know that most individuals carry some unfavorable recessive genes. The more genetic tests that are developed, the greater chance there is of identifying an undesirable gene. Remember, however, that an animal is not a single gene, an eye, a hip, or a heart. Each individual carries tens of thousands of genes, and each is a part of the breed’s gene pool. When considering a mating, breeders must consider all aspects – such as health issues, conformation, temperament and performance – and weigh the pros and cons.

Without tests, the management of genetic disease involves breeding higher-risk animals to lower-risk animals. Occasionally, a breeding male is determined to not carry a defective gene for which there is no carrier test. The tendency is for everyone to breed to this male, as a guarantee against the disorder.  Any major shift in the breeding choices to a limited number of males will restrict genetic diversity, and increase the possibility of propagating additional undetected defective recessive genes in a breeding population. Such genes have become widespread even in populous breeds due to prolific breeding of popular sires.

Breeders are the custodians of their breed’s past and future. “Above all, do no harm” is a primary oath of all medical professionals. Genetic tests are powerful tools, and their use can cause significant positive or negative changes. Breeders should be counseled on how to utilize test results for the best interests of the breed.

This article can be reproduced with the permission of the author. Jerold.Bell@tufts.edu

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Breeding Strategies for the Management of Genetic Disorders

Jerold S Bell DVM, Clinical Associate Professor of Genetics, Tufts Cummings School of Veterinary Medicine

With each new generation of dogs, breeders ask, “How can I continue my line and improve it?” Aside from selecting for conformation, behavior and ability, breeders must consider how they are going to reduce the incidence of whichever genetic disorders are present in their breed. There are no answers that will fit every situation. There are, however, guidelines you can follow to preserve breeding lines and genetic diversity while reducing the risk of producing dogs that carry defective genes, or are affected with genetic defects.

Autosomal Recessive Disorders
In the case of a simple autosomal recessive disorder for which a test for carriers is available, the recommendation is to test your breeding- quality stock, and breed carriers to normal-testing dogs. The aim is to replace the carrier breeding- animal with a normal-testing offspring that equals or exceeds it in quality. You don’t want to diminish breed diversity by eliminating quality dogs from the gene pool because they are carriers. As each breeder tests and replaces carrier dogs with normal-testing dogs, the problem for the breed as a whole diminishes.

For some disorders there are tests known as linkage-based carrier tests, which can generate a small percentage of false positive and negative results. When using these tests to make breeding decisions, it’s advisable to first determine whether the results correlate with the test results and known genotypes of relatives.

When dealing with a simple autosomal recessive disorder for which no carrier test exists, breeders must assess whether each individual dog in their breeding program is at high risk of being a carrier. This requires knowledge of the carrier or affected status of close relatives in the pedigree. An open health registry that is supported by the parent club makes it easier for breeders to objectively assess these   matters. By determining the average carrier-risk for the breeding population, breeders can select matings that have a projected risk which is lower than the breed average.

If breeding a dog that is at high risk of being a carrier, the best advice is to breed to a dog that has a low risk. This will significantly diminish the likelihood that affected dogs will be produced, and can reduce by up to half the risk that there will be carriers among the offspring. Using relative-risk assessment as a tool, breeders should replace higher-risk breeding dogs with lower-risk offspring that are equal to or better than their parents in quality. Relative-risk assessment allows for the continuation of lines that might otherwise be abandoned due to high carrier risk.

Breeding a dog only once and replacing it with an offspring allows breeders to improve their chances of moving away from defective genes and also limits the dissemination of defective genes. When dealing with disorders for which carriers cannot be identified, the number of offspring placed in breeding homes should be kept to a minimum.

Autosomal Dominant Disorders
Autosomal dominant genetic disorders are usually easy to manage. Each affected dog has at least one affected parent, but it can be expected that half of the offspring of an affected dog will be free of the defective gene. With disorders that cause death or discomfort, the recommendation is to not breed affected dogs. To produce the next generation of a line, a normal full sibling of an affected dog can be used, or the parent that is normal can be used.

A problem with some autosomal dominant disorders is incomplete penetrance. In other words, some dogs with the defective gene may not show the disorder. Roughly half their offspring, however, may be affected.  If a genetic test is available, this is not a problem. Otherwise, relative-risk assessment can identify which dogs are at risk of carrying incompletely penetrant dominant genes.

Sex-Linked Disorders
For sex-linked (also known as x-linked) recessive defective genes for which carrier tests exist, breeders should follow the same “breed and replace” recommendations as are outlined above in the discussion of autosomal recessive disorders. If there is no test, the defective gene can be traced through the pedigree. If a male is affected, he would have received the defective gene from his carrier mother. All of his daughters will be carriers, but none of his sons. By using relative- risk assessment to breed him to a female that is at low risk of being a carrier, you can prevent affected offspring, and select a quality son for replacement.

There are rare instances in which a female is affected with a sex-linked disorder. In such cases, she would have received the defective gene from both parents; specifically, an affected father and a mother who is either a carrier or is affected herself. If an affected female is bred, all the sons will be affected, and all the daughters would be carriers, so affected females clearly should not be bred. A normal male that is a littermate to an affected female, however, would be able to carry on the line without propagating the defective gene.

Sex-linked dominant disorders are managed the same way as autosomal dominant disorders are. The difference is that affected males will always produce all affected daughters.

Polygenic disorders
Polygenic disorders are those caused by more than one pair of genes. Most polygenic disorders have no tests for carriers, but they do have phenotypic tests that can identify affected dogs.With polygenic disorders, a number of genes must combine to cross a threshold and produce an affected dog. These are known as liability genes. In identifying a dog’s liability for carrying defective genes for  a  polygenic disorder, the breadth of the pedigree (that is, consideration of all siblings of individuals in the pedigree) is more important than the depth of the pedigree (consideration only of parent-offspring relationships.) A clinically normal dog from a litter that had one or no individuals affected with hip dysplasia (which is a polygenic disorder) is expected to carry a lower amount of liability genes than a dog with a greater number of affected littermates. This is why it is important to screen both pet and breeding dogs from your litters for polygenic disorders. Information on the siblings of the parents of potential breeding dogs provides additional data on which to base your breeding decisions.

Genetic disorders without a known mode of inheritance should be managed in the same way as polygenic disorders. If there are multiple generations of normalcy in the breadth of the pedigree, then you can have some confidence that there are less liability genes being carried. If a dog is diagnosed with a genetic disorder, it can be replaced with a normal sibling or parent and bred to a mate whose risk of having liability genes is low. Replace the higher-risk parent with a lower-risk offspring that equals or exceeds it in other aspects, and repeat the process.

Genetic tests are extremely useful tools to help manage genetic disorders. Even when there is no test, or a known mode of inheritance, much can still be done to reduce the incidence of affected and carrier animals. The use of these guidelines can assist breeders in making objective breeding decisions for genetic-disease management, while continuing their breeding lines.

This article can be reproduced with the permission of the author. Jerold.Bell@tufts.edu

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The Aspect of Population Size on Healthy Breeding in Dog Breeds

By Jerold S Bell DVM

Cummings School of Veterinary Medicine at Tufts University, USA jerold.bell@tufts.edu

This article originally appeared in the proceedings of the 2017 AKC Canine Health Foundation National Parent Club Canine Health Conference. It can be reprinted with written permission from the author.

A large number of individual dogs in a breed population allow greater choices when making breeding decisions. Multiple breed “family lines” support greater breed diversity; the genetic difference between individuals in the breed. When selecting on several different traits or disorders, a large population should allow for several choices of mates that fulfill different selection preferences. A goal of all breeds is to grow and maintain a large, diverse and healthy population.

All breeds originate from a small population of either related dogs or dogs who share a common conformational, behavioral, or working phenotype. Through selection, a breed standard is developed. Individual dogs that do not adhere to the standard or who demonstrate deleterious traits or disorders are purged from breeding. Those individuals who demonstrate and propagate desirable characteristics will have an increasing influence on the gene pool through multiple generations of descendants. Once breed characteristics are fixed in the population, it can go through an expansion stage where the population grows.

Figure 1
Figure 1

Fig. 1: Pedigree of a typical purebred dog (individual at the left). Breed founders appear at the right, and the breed goes through a purging stage, and then expansion stage.

All breeds will have several influential ancestors that appear far back in pedigrees, but pass on a high percentage of their genes to every individual in the breed. For example, all Bichons Frises share on average 17.5% of their genes with Pitou (born in 1924), which is between the contribution of a grandparent and great-grandparent. He does not appear on average until the 16th generation, but appears over 4 million times in every Bichon pedigree and 38% of his alleles have been retained in the breed population. Bearded Collie Bailie of Bothkennar was born in the 1940s, and contributes 32.6% of his genes to every modern Beardie.

This process of breed evolution causes a loss of genetic diversity through the purging of undesirable individuals and the concentration of genes of influential ancestors. All breeds are partial clones of their influential ancestors. This is an expected consequence of breed evolution and is not detrimental to the breed.

Genetic disorders can be due to ancient disease liability genes that preceded breed formation and are shared by many breeds, or by recent mutations that cause breed-specific disease. These can originate from a random mutation and be propagated through breed ancestors. Conversely, genes causing genetic disorders can be linked on a shared chromosome to a selected trait (ex., hyperuricosuria and Dalmatian spotting), or genetic disorders can be caused by direct selection for disease-causing phenotypic traits (ex., brachycephalic obstructive airway disease).

IS POPULATION SIZE DIRECTLY CORRELATED TO BREED HEALTH?

Evidence from registration figures and valid breed health surveys show that the size of a population does not determine whether the breed will suffer from higher frequencies of genetic disease. There are many large population breeds with high frequency genetic disorders, and many small population breeds that show excellent health. In a small population breed, individual mating choices and individual litters have a greater effect on the breed frequency of disease liability genes because they represent a larger percentage of the total gene pool. It is the lack of selection for genetic health in either large or small population breeds that allows the propagation of genetic disorders. Breed genetic health depends on selection against disease liability genes regardless of the size of the population.

DOES A LARGE POPULATION AUTOMATICALLY CONFER GENETIC DIVERSITY?

When analyzing entire breed population databases back to founders, every dog breed – regardless of its population size – has the same findings; high homozygosity and low effective population size (minimum number of ancestors explaining the complete genetic diversity of a population). These are necessary and expected consequences of breed formation and evolution. As a breed gene pool expands, the average recent generational relationship (inbreeding and kinship) between mates can decrease. However, the average total generational relationship between dogs back to founders does not decrease. Breeds with small populations look the same as breeds with large populations did much earlier in their evolution and development.

In both large and small population breeds, genetic diversity can be lost if breeders do not utilize dogs from the breadth of the gene pool. This is most evident in the popular sire syndrome. This can be compounded when a popular sire is replaced by a popular son, who is replaced by a popular grandson, and the entire breed truncates on a single popular sire line. This causes a loss of genetic diversity from the breadth of the gene pool that would be propagated from other quality male lines.

Another issue with popular sires is that their genetic contributions can only be evaluated after their prolific breeding period is over, and their genes have already been disseminated throughout the gene pool. Many recently identified genetic disorders that rise in frequency in a breed are caused by genes carried by popular sires. This is different from an influential ancestor, whose qualities and influence are constantly evaluated every generation. If an influential ancestor’s descendants are not producing quality, then they are not bred and the ancestor’s influence diminishes. With the popular sire syndrome a breed population may expand in numbers, but if breeding is concentrated in only a portion of the gene pool genetic diversity will diminish.

Some breeds may lack enough health and vitality from the start, and these breeds collapse and do not progress beyond the purging stage of development. Other breeds may have a robust and growing population, but due to other factors experience a population contraction and decline that could significantly eliminate the genetic diversity present in the gene pool. The recent economically induced decline and then rise in AKC registrations is not detrimental to a breed as long as it was a temporary slowing, and not a loss of breeding lines. Frozen semen is also an important hedge against the loss of diverse lines. Population contraction is a serious detriment to breed genetic diversity if it includes the loss of diverse within-breed lines. In extreme cases, a breed may require opening up its stud book to bring new genes into its gene pool. However most current dog breeds show acceptable genetic diversity and only require health conscious breeding and population expansion to maintain their gene pools.

DO OUTBREEDING PROGRAMS IMPROVE GENETIC DIVERSITY AND GENETIC HEALTH?

Conservation geneticists versed in rare and endangered species have designed species survival plans (SSPs) that call for outbreeding; mating together animals that are least related to each other. The purpose of SSPs is to prevent the homozygous expression of deleterious recessive genes. However, natural species and artificially selected breeds have completely different, and in many instances completely opposite selection pressures and desired outcomes. SSPs call for using all available individuals in breeding and only outbreeding. Dog breeding calls for selection, which requires differences between prospective mates and therefore genetic diversity between individuals.

Outbreeding homogenizes the population by removing the genetic difference between individuals in the breed and making everyone “alike”. If two unrelated parents are bred together, the offspring make the two lines related. If an offspring is then outbred to a further unrelated line, their offspring make all of the lines related. Outbreeding is a self-limiting process as there will eventually be no unrelated dogs. In order to have selective pressure for positive traits and against negative traits or disorders, there must be variation and genetic differences between individuals in the gene pool. This requires distinct family lines that are eliminated by outbreeding programs.

Thus, the basic conceptual point is, “What constitutes genetic diversity?” Is it the diversity within each dog (heterozygosity through outbreeding)? Or is it the diversity between each dog (maintaining diverse family lines)? These two concepts are diametrically opposed to each other and breeders and breed organizations must decide which is in the best interest of their breeds.

The genes causing common breed-specific genetic disorders have already been dispersed in breed gene pools. Therefore the chance of breeding two carriers together is based on the frequency of the deleterious gene(s) in the population, and not necessarily the type (outbreeding or linebreeding) of mating. Outbreeding propagates deleterious genes in the carrier state and randomizes the occurrence of genetic disease; the same as is seen with common genetic disorders in mixed-breed dogs. The only way to select against specific genetic disorders is to specifically select against the causative or liability genes through direct genetic testing or phenotypic genetic screening.

ADDITIONAL FACTORS IN SMALL POPULATION BREEDS

Small population breeds have added issues because each mating has a much greater influence on the entire gene pool. If a breed has particular hereditary disorders at a higher frequency, mates should be selected that can minimize or lower the risk of producing these disorders. A quality higher risk dog (closely related to affected) can be bred to a lower risk dog and replaced with a lower risk offspring. As this process is repeated, the carrier risk and deleterious gene frequency will diminish in the population. As most disorders are complexly inherited and have no tests for carriers, carrier risk must be based on knowledge of phenotypic pedigree depth (parents and grandparents) and breadth (littermates and littermates of parents).

Some breeders in small population breeds are afraid to breed and possibly cause more disease. However if no breeding is going on, the breed will certainly become extinct. Mates must be selected that reduce the risk of producing genetic disorders. Breeders need to do their best to select for health and quality and then see what they produce.

In small population breeds a greater number of offspring should be placed in breeding homes to expand the population. However, breeders of some small population breeds try to constrain breeding and limit it only to themselves. This is a shortsighted attitude. Breeders should recruit and mentor puppy buyers to become thoughtful breeders. As a population expands, the choices of mates increase and the average recent relatedness of mates will decrease. Decreasing average recent generational inbreeding coefficients is a natural consequence of expanding populations utilizing the breadth of their gene pools. It does not need to be artificially manipulated. Breeders all doing something a little different with their mating choices – i.e., which individuals they are selecting, the types of matings utilized, etc. – is what maintains breed genetic diversity. With health conscious breeding, there are greater choices available to produce healthier offspring.

CONCLUSIONS

All breeds require expanding or large, stable breeding populations. Mates should be selected that represent the breadth of genetic diversity in the gene pool. It is mate selection and not the types of matings that they are involved in (linebreeding or outbreeding) that maintains genetic diversity.

Large and small population breeds show the same population indices of; high homozygosity, low effective population size, and high relationship to influential ancestors. The difference between large and small populations is in the available choice of breeding individuals.

Health conscious selection through breed-appropriate genetic screening of prospective breeding individuals is the most important aspect of improving and maintaining the genetic health of any breed, regardless of its population size.

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Reproduction Link Resources

Canine Genetics for Dog Breeders: Part 1
By Dr. Matthew Breen, Jun 15, 2018 Learn more

The Ins and Outs of Pedigree Analysis, Genetic Diversity, and Genetic Disease Control, Author: Dr. Jerold Bell  Learn more

Progesterone Testing and Ovulation Timing
Source: Canine Semen Bank of Columbus Learn more

A Beginner’s Guide to COI (Coefficient of Inbreeding)
Dog Breed Health: A Guide to Genetic Health Issues for Dog Breeds
Written by Jemima Harrison: Learn more

Inbreeding – using COIs (Coefficient of Inbreeding)
The Kennel Club: Learn more

Population analysis of the Basset Griffon Vendeen (Petit) breed
The Kennel Club, September 2015: Learn more

Basset Griffon Vendeen (Petit)
Dog Breed Health: A Guide to Genetic Health Issues for Dog Breeds
Learn more

Canine Infertility·· A Silent Threat – Mycoplasmia Infection
By R.M. Brown, D.V.M . Learn more

Test for this Hidden Killer Before Breeding
By Susan Chaney, Posted in: Canine Health, Right Now! | March 1, 2012
Brucellosis could easily be called the AIDS of the dog world. Although not as common, it is more easily spread, is always fatal to puppiescarried by an infected bitch and has no cure. Learn more

Gonadectomy – Rethinking Long-Held Beliefs (2018)
Chris Zink DVM PhD, DACVP, DACVSMR, CCRT, CVSMT, CVA
Canine Sports Productions – www.caninesports.com
Those of us with responsibility for the health of dogs need to continually read and evaluate new studies to ensure that we are taking the most appropriate care of our canine companions. This article reviews scientific evidence that, taken together, suggests that veterinarians and dog owners should revisit the current common recommendation that all dogs not intended for breeding have their gonads removed at or before 6 months of age…   Learn more

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Canine Mycoplasma: It’s Role in Reproductive Disease

By Janice Cain, DVM and
Melissa Goodman, DVM

(Source: International Canine Genetics, Inc. News February 1994, pp. 1, 4.)

Mycoplasma infections have been implicated as a cause of infertility in both bitches and stud dogs. As a result, mycoplasma continues to receive attention as a potential concern for purebred dog breeders. The following article discusses what is currently known about canine mycoplasma infections and outlines a management approach for breeding animals.

WHAT IS MYCOPLASMA?
Mycoplasmas are bacterial organisms that, because of their extremely small size, have been placed in a separate class. Also, unlike any other bacteria, mycoplasmas lack a rigid cell wall which makes them unaffected by antibiotics that act by invoking cell wall damage (for example, penicillin). Mycoplasmas are extremely fastidious organisms that are difficult to culture without special media, and even then may be difficult to recover. Ureaplasmas are a distinct type of mycoplasmas that have been subclassed and are identified by their own name.

MYCOPLASMA AS PART OF THE NORMAL FLORA
Several mycoplasma species have been found to be normal inhabitants of the upper respiratory and genital tracts of dog and cats, and as a result they can be routinely isolated from oral, nasal, conjunctival and genital mucous membranes. Several studies have specifically looked at the frequency of mycoplasma recovery from the genital tracts of fertile versus infertile bitches and stud dogs, and no significant difference has been found. (1,2) Therefore, recovery of mycoplasma from a vaginal or semen culture does not always correlate to reproductive disease, and likewise does not always need to be treated. Since these organisms exist in the respiratory tract as well as the reproductive tract, aerosol transmission from dog to dog (airborne. licking, sniffing, etc.) is probably more frequent than venereal transmission.

WHEN TO WORRY ABOUT MYCOPLASMA?
While mycoplasmas may be normal inhabitants of the reproductive tract, they have been associated with infertility, lesions of the reproductive tract and sperm abnormalities. (3.4.5)As with many opportunistic pathogens (organisms that may cause disease but frequently don’t) clinical disease often results when an animal is under stress and/or exposed to high numbers of organisms. Close intensive housing conditions (as in a large kennel or at indoor dog shows) provide the opportunity for high numbers of organisms to develop. A healthy dog or bitch especially if housed individually, however, may not become diseased even after known exposure to the organism.

It has been found that the administration of broad spectrum antibiotics may suppress many other bacteria that make up normal flora and allow mycoplasmas to overgrow. Therefore, the prophylactic use of antibiotics prebreeding is not recommended as it may actually create a pathogenic state, and may contribute to the development of antibiotic-resistant populations of organisms.

A mycoplasma culture should be performed if:

1) A dog has missed several bitches (i.e., no conception).
2) A semen evaluation shows morphologically abnormal sperm cells.
3) A bitch has not conceived having been bred to a fertile stud dog on appropriate days.
4) A dog or bitch produces conception but has a documented high rate of fetal resorption.

It is important to remember that there are many other causes of the above problems, and so a mycoplasma culture should be only one part of a thorough diagnostic investigation performed by a veterinarian experienced in canine reproduction.

PROPER MYCOPLASMA CULTURE TECHNIQUE
Due to their fastidious nature, mycoplasmas require special techniques for successful growth in cultures. As a result, mycoplasma cultures should only be sent to laboratories competent in the recovery of the organism. It is recommended that ureaplasma is cultured for at the same time, since it is a similar organism and has also been implicated in infections of the reproductive tract. (1)

Proper technique in obtaining the sample to be cultured is also extremely important. In bitches, it is recommended that the vaginal area close to the cervix be sampled using a guarded swab. In stud dogs, it is important that a semen specimen be collected using sterile technique, avoiding urethral contaminants.

WHAT TO DO ABOUT NORMAL FERTILE DOGS AND BITCHES!
Since mycoplasma is frequently cultured from the vagina of normal fertile bitches, routine prebreeding cultures of bitches are not warranted. Since mycoplasma is frequently recovered from cultures of the prepuce and/or semen of normal fertile males, routine prebreeding cultures may show some growth of mycoplasma as part of the normal flora However, some owners may choose to periodically have a dog’s semen cultured for mycoplasma. While a negative result is definitive, the significance of a positive result must always be determined by correlation to semen evaluation and clinical condition. Unfortunately, a dog’s fertility status cannot be determined on the basis of mycoplasma recovery.

SUMMARY
Mycoplasma infection is only one of many factors that may impact canine fertility. Working with an experienced veterinarian with a thorough, systematic approach to investigating fertility problems will pay dividends to your breeding program.

A guarded swab recommended for proper vaginal culturing in bitches is available through TCG. Veterinarians may order the Accu-CulShure® Specimen Collection/Transport System by calling TCG at 800-248-8099.

1. Doig PA, Ruhnke HL, Bosu WTK: The genital mycoplasma and ureaplasma flora of healthy and diseased dogs. Can J Comp Med 45:233, 1981.

2. Bjurstrom L, Linde-Forsberg C: Long-term study of aerobic bacteria of the genital tract in stud dogs, Am J Vet Res 53:670-673, 1992.

3. Lein DH: Mycoplasma infertility in the dog: diagnosis and treatment. Proc SFT, Sept 1989, p. 307-313.

4. Holzmann A, Laber G: Experimentally induced mycoplasmal infection in the genital tract of the male dog. Therio 7(4): 167-188, 1977.

5. Lingwood CA et al: Common sulfoglycolipid receptor for mycoplasmas involved in animal and human infertility. Biol of Reprod 43:694-697, 1990.

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Using Canine Nomographs to Better Time Puppy Vaccinations

 

© 2017 Avidog International LLC

INTRODUCTION

We were introduced to canine nomographs 15 years ago by Dr. Ronald Schultz from the University of Wisconsin’s School of Veterinary Medicine. Since then, we have used them to time our pups’ vaccinations. This simple, inexpensive tool has enabled us to overcome the two conflicting pressures that dog breeders face— how do we ensure every puppy is fully socialized during its first 16 weeks of age while keeping them safe from distemper and parvovirus?

Nomographs have proven to be the answer for us and thousands of our colleagues and students. So, with the help of Dr. Laurie at the Schultz Lab, we have written this ebook for other breeders. We hope it will be useful to you!

Like you, we are simply dog breeders so be sure to discuss this process with your veterinarians! Feel free to share this booklet with them.

Gayle, Marcy and Lise

Our thanks to the Schultz Lab, Dr. Ron Schultz and Dr. Laurie Larson for providing this invaluable service to dog breeders and puppy owners across North America!! Please visit the lab’s website for more information and details.

https://www.vetmed.wisc.edu/lab/Schultz/

WHAT ARE CANINE NOMOGRAPHS?

Nomographs are simple blood tests that estimate the amount of distemper and parvovirus antibodies passed from a dam to her puppies via her colostrum, or first milk. Nomographs are useful for breeders and puppy owners because they can help predict when pups:

  • are no longer protected by maternal antibodies and
  • will be able to respond to distemper and/or parvo vaccines.

During a puppy’s first 12 hours of life, its intestinal tract allows antibodies in colostrum to pass into the bloodstream and thus start protecting it from the diseases that its mother is protected from. As the puppy grows up, maternal antibodies break down in approximately two-week “half lives” until they are no longer present in the pup.

While a puppy’s maternal antibodies are high, they neutralize viruses such as canine parvovirus and canine distemper virus. This keeps the pup safe from these potentially fatal diseases. However, this same neutralization also blocks vaccines so the puppy will not able to be immunized.

Maternal antibodies against distemper and parvo are independent of each other; a bitch can and usually will have different levels of protection against these diseases. In our experience, bitches’ titers can range from as low as 4 and as high as 5280. These levels mean a pup’s maternal antibodies can disappear as early as a few days after birth to as late as 18 weeks of age! With these last pups, if we had stopped vaccinating them at 16 weeks, as is commonly done, the pups would not have been protected!

In fact, maternal antibody interference is one of the most common causes of vaccine failure in puppies! We usually give pups multiple doses of vaccine every two to three weeks during puppyhood because we don’t know their maternal antibody titers. So, we don’t know when a vaccine will be effective. Nomograph testing helps us understand the best timing of vaccination to ensure a litter will be effectively immunized with the fewest vaccines as early as possible in their life.

We can measure the antibodies that a bitch has to pass on to her puppies using antibody titers, a simple blood test. If that test is done at the Schultz Laboratory at the University of Wisconsin Veterinary School, a nomograph can then be run on those results, allowing us to predict the optimal time to vaccinate her puppies.

USING A NOMOGRAPH FOR YOUR LITTER
To use a nomograph to better time your litter’s distemper and parvo vaccinations, you will need to ship serum from your bitch to the Schultz lab. The ideal time for the blood draw is either two weeks before or two weeks after the puppies are whelped. You may find it more convenient to do the blood draw when your bitch is at your veterinarian’s for progesterone testing or a pregnancy ultrasound. Similarly, bitches that are bred more than once a year do not have to have a second nomograph that year. However, the further from whelping the blood is drawn, the more risk you take that your bitch has come in contact with distemper or parvo and mounted an immune response that won’t be revealed in her titer. You’ll have to decide how great that risk is based on your bitch’s activities and the amount of parvo or distemper in your area. Personally, we stick with drawing blood either two weeks before or two weeks after whelping.

Prepare and ship the blood according to the Blood Preparation Procedures in the next section and the Nomograph Submission Form on page 10. Follow the example submission form on page 11. It is particularly helpful to the lab if you provide your dam’s vaccination history. At a minimum, fill out her distemper (CDV) and parvovirus (CPV-2) vaccination history.

Nomograph Report. In about a week, you will receive an email report from the lab similar to the one on page 12. The report will give you your bitch’s parvo and distemper titers in the box, and then below that is the protective standard for this lab. A little further down the page will be the nomograph information for the litter, indicating the age at which the pups can be vaccinated and for which diseases. On these reports, D indicates a distemper vaccine, A indications an adenovirus-2 vaccine, and P indicates a parvovirus-2 vaccine. The report then goes on to give further information about confirming the pups’ immune response.

Pups’ “At-Risk” Period. Prior to the recommended vaccination dates, the pups are at risk for getting distemper or parvo if they come in contact with it. At the same time, it is critical that we fully socialize and develop our pups prior to 16 of age. So breeders must practice good biosecurity while still socializing puppies during the weeks prior to the vaccinations. If you want to know more about how to do this, check out Avidog’s Transformational Puppy Rearing video series (www.avidog.com/request-rbp-vod/).

Send Reports to New Homes. Provide a copy of the nomograph report with each pup’s vaccination record to its new owners so they can provide them to their veterinarian on the first visit. This enables the pup’s vet to tailor the pup’s vaccines to its individual needs.

Confirming Pups’ Responses to Vaccines. Every pup, no matter what vaccination protocol it receives, should have a confirmatory titer drawn to ensure that it is protected. We have personally bred litters that could and did not respond to the parvo vaccine until after 17 weeks of age. If their owners had stopped vaccinating at the typical 16 weeks, those pups would have been left unprotected against parvo. They would have had a good chance of coming down with the disease in their first year, since they were competition dogs and thus out and about.

You or your owners can use the Schultz lab for your pups’ confirmatory titers. Use the same submission form and blood draw instructions but this time, do not check the nomograph block. Attach a copy of the dam’s nomograph with the submission form. You will receive a report like the one on page 13.

If an owner doesn’t do a confirmatory titer after the puppy series, that pup should be vaccinated against distemper, parvo and adeno at a year of age, when all chance of maternal antibodies is gone.

High Risk Conditions. In high risk situations, such as kennels that have had parvo outbreaks, you should take the additional step of running a titer on at least one pup in a litter BEFORE vaccination is begun. The nomograph on the dam is helpful, but a pup’s actual antibody level provides even better information in this risky situation.

When Not to Use Nomographs. Nomographs are useful tools to help breeders predict when vaccinations can be successful in their pups. However, to successfully use nomographs to schedule a puppy’s distemper and parvovirus vaccines, that puppy must have ingested colostrum from its dam during its first 12 hours of life. If for some reason that did not happen, either due to issues with the puppy or its mother, then a nomograph cannot be used and the puppy should be vaccinated using the more standard vaccination protocols, like those recommended by the World Small Animal Veterinary Association, which can be found at www.wsava.org/guidelines/vaccination-guidelines.

BLOOD PREPARATION PROCEDURES FOR A NOMOGRAPH

☐ Plan to draw your bitch’s blood two weeks prior to or two weeks after whelping. Avoid drawing blood closer to whelping than these dates because the bitch’s body is creating colostrum and the nomograph will be less accurate. At the same time, if you draw her blood too far from whelping, you risk her coming in contact with distemper or parvo closer to whelping, which will change the antibody levels the pups get in her colostrum.

☐ Ship your bitch’s blood to arrive at the lab Monday through Friday. Drawing and shipping blood Monday, Tuesday or Wednesday is usually best.

☐ Collect 1 to 3 mls of blood from your bitch in a sterile, red top or serum separator tube and allow it to clot.

☐ Spin down to separate the serum. Send at least ½ ml of serum for the testing.

☐ Wrap the tube with the serum in padding, such as paper towel, and place it in a plastic zip-lock bag.

☐ Fill out the submission form (see sample form) and place it with a $25 check made payable to the University of Wisconsin in a SECOND plastic zip-lock bag. (Please note this fee is expected to go up at some point in 2017, so you may want to call the lab to ensure you send the proper amount.)

☐ Place both plastic bags in a sturdy shipping container, either a padded envelope or box. If the ambient temperature might go above 80°F during shipping, include a cold pack wrapped with some newspaper to keep it from crushing the serum vial. Freezing temperatures aren’t a concern when shipping separated serum.

☐ Send the shipping container via USPS 2-day Priority Mail to this address. Overnight shipping is not necessary.

Dr. R.D. Schultz Laboratory
4337 School of Veterinary Medicine
2015 Linden Drive West
Madison, WI 53706
(608) 263-4648

☐ The lab usually runs tests on Fridays and will send you and your vet a report via email (see sample report) that gives you the following, usually a week after receiving the blood sample:

  • your bitch’s quantitative titers for distemper and parvo,
  • an interpretation of these results for her, and
  • recommendations for which weeks to vaccinate her puppies.

RESOURCES

American Veterinary Society of Animal Behavior. 2008. AVSAB Position Statement On Puppy Socialization. Available at http://www.avidog.com/wp-content/uploads/2014/02/AVSAB-Position-on-Puppy-Socialization.pdf

Baker JA, Robson DS, Gillespie JH, Burgher JA, Doughty MF. 1959. A nomograph that predicts the age to vaccinate puppies against distemper. Cornell Vet. 1959 Jan;49(1):158–167.

Ronald D Schultz Lab. 2016. Canine Nomograph – What is it? Available at www.vetmed.wisc.edu/lab/schultz/canine-nomograph-what-is-it/

WSAVA Vaccination Guidelines Group. 2015. World Small Animal Veterinary Association 2015 Vaccination Guidelines for The Owners and Breeders of Dogs and Cats. Available at http://www.avidog.com/wp-content/uploads/2016/12/WSAVA-Owner-Breeder-Guidelines-14-October-2015-FINAL-1.pdf

NOMOGRAPH SUBMISSION FORM For Dr. R.D. Schultz Lab Click Here

Avidog International provides continuing professional education for dog breeders based on current and past research, as well as over 60 years of joint breeding experience.  Visit our Breeder College for courses, products, ebooks and more.

Avidog International LLC
PO Box 959
Mattituck, NY 11952
info@avidog.com
(800) 305-2808 
www.Avidog.com

(PBGVCA does not provide specific medical advice, but rather provides users with information to help them better understand health and disease. Please consult with a qualified health care professional for answers to medical questions.)

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