Conclusions from the 1997-1998 Chinook Health Survey
TUFTS 1997-1998 CHINOOK BREED HEALTH SURVEY
Jerold S. Bell, D.V.M.
Clinical Assistant Professor of Genetics
Department of Clinical Sciences
Tufts University School of Veterinary Medicine
North Grafton, Massachusetts
This cover report accompanies the data report on the Chinook Breed Health Survey. There was a good response rate to the survey, with 49.04% returning surveys. The majority of dogs still reside in Maine and the other New England states, although Chinook populations are growing in other areas of the country. The vast majority of respondents felt that canine hip dysplasia is the most important health problem facing the breed. A limited gene pool was also a concern, and will be addressed in the Chinook Genetic Diversity Study. Epilepsy and retained testicles (cryptorchidism) were also singled out as problems, and the concern for these three mentioned hereditary disorders is supported by the data.
Any survey such as this cannot attempt to identify the true frequency of disease or health in the breed. While the response rate is good based on registration figures, healthy dogs are under reported in most surveys. While this tends to overestimate the frequency of disorders in the breed, repeated diagnoses suggest problem areas. The relative frequency of diagnoses can be compared with each other to rank the prevalence or importance of disorders in the breed. The inclusion of Chinook cross data allows comparison, and provides important information on the frequency of diagnoses.
There is a large population of purebred Chinooks, with a large population of possible breeding (sexually intact) dogs. Chinooks appear to live a normal lifespan, and based on the age distribution, there is an increasing population. There is more variation in height and weight than found in many other breeds. This may relate to the fact that the breed was created from diverse origins based on working ability, and not a conformational standard. The colors, eye color, and ear set are similarly varied.
A smaller population of Chinook crosses is similarly long lived, with a young breeding population. The population represents the influence of several different breeds. The population shows averages similar to the purebred population, with variation in height, weight, color, eye color, and ear set.
Litters of purebred Chinooks do not show a decrease in litter size that might be expected with an inbred population. There was no significant difference in litter size between purebred and crossbred Chinooks. Stillborn puppies, not due to dystocia or uterine infection occurred at a frequency of 3.8%. This corresponds to one puppy per every four litters, which is slightly higher than the average canine population. There was a significant occurrence of hydrops or hydrocephalus puppies, with one occurring in four different litters between 1982 and 1996. Reports of birth defects were higher than canine averages, but included 9.7% of males with cryptorchidism. This was not considered a birth defect on the litter form, and will instead be addressed in the breed diagnoses. Without these dogs, an 8.6% frequency of birth defects remains high. Hydrops/hydrocephalus and umbilical hernia top the list with frequencies of 2.2% each. Color of puppies listed showed a significantly higher percentage of silver/gray dogs than that recorded in the adult population. From the Chinook cross litters, there was again a varied population, with only one stillborn puppy, and no birth defects recorded.
In the survey data of individual dog diagnoses, 41.8% of purebred Chinooks, and 59.2% of Chinook crosses had no disease listed. The frequency of diagnoses by category
mirrored the frequently diagnosed individual disorders contained within them. In compiling the list of specific disorders, three were added as combinations of separate diagnoses, based on our knowledge of the inheritance of these disorders. Cryptorchidism- Unilateral (11) and Cryptorchidism-Bilateral (7) were combined to Total Cryptorchidism. Hip Dysplasia-Subluxation (12), Hip Dysplasia-Other (4), and Hip Laxity (1) were combined to Total Hip Dysplasia, while ensuring that individual dogs were not listed in more than one category. Epilepsy or Hereditary Seizures (10) and Non-Epileptic Seizures (10) were combined to All Seizure Disorders, as these two diagnoses cannot be differentiated clinically.
DISCUSSION OF TOP TEN DIAGNOSES
Total Cryptorchidism topped the list of Chinook diagnoses with a startlingly high 14.63% of all male dogs affected. Cryptorchidism-Unilateral had 11 diagnoses to be the second most frequent (8.94%) diagnosis for the breed, and Cryptorchidism-Bilateral had 7 diagnoses to be the ninth most frequent (5.69%) diagnosis for the breed. Litter survey forms had 9.7% of male puppies with retained testicles, including some where all males in the litter were affected. Cryptorchidism is defined as the failure of one or both testicles to descend into the scrotum by eight weeks of age. The reported incidence of retained testicles in the general canine population is approximately 0.8%. Unilateral and bilateral retained testicles are caused by the same genetic process, as is delayed descent of the testicles into the scrotal sac (which was not surveyed for). It is known that this is a sex limited disorder (females cannot express the trait). Females, including dams and littermates of affected dogs, can be genetically affected and pass on the trait at the same frequency as affected males. The mode of inheritance of cryptorchidism has not been established. The fact that Chinook crosses also had a significantly high percentage of diagnoses may suggest a major dominant influence. Conversely, many experts feel that this may be a polygenic trait, where a threshold of genes must combine to produce the disorder. With the high prevalence of the disorder in purebred Chinooks, they may pass on enough defective genes to cause crossbred dogs (not necessarily first generation) to express the trait. A genetic study of the relationship of these dogs should be investigated, and more data should be collected on dogs with cryptorchidism, and those with late descending testicles. Even if these frequencies are overestimated, this is an alarmingly high number of diagnoses for a rare breed.
All Seizure Disorders was tied for the third most frequent (8.37%) diagnosis with 20 dogs recorded. Ten dogs were listed with Epilepsy (tied for 12=4.18%) and ten dogs were listed with Non-Epileptic Seizures (tied for 12=4.18%). The clinical descriptions of the seizure disorders in these two groups overlap, and could not be differentiated. The onset of seizures ranged from 9 weeks, to six years of age, with most between 9 months and four years of age. Six dogs had their first seizure at less than one year of age, seven dogs between one and three years of age, five dogs between three and five years of age, one at six years of age, and one with no age recorded. Most dogs had multiple seizures, but four of the twenty have had only one seizure recorded to date. Three of the twenty had multiple seizures over at least a one year period, but have not observed any since then. Chinook crosses had three dogs with seizures (4.23%); one that was eventually euthanized due to seizures, and two that had recurrent seizures, for one and four years duration, but none since then. The high frequency of Chinooks and Chinook crosses with seizures of any kind is significant. While it is not infrequent to see dogs with single seizures who never seize again, these are occurrences across all breed lines; not clustered within the same breed. Some genetic mechanism is causing Chinooks and Chinook crosses to have seizures at a much higher rate than the general canine population. Epilepsy is known to be a group of different genetic disorders, which must be separated based on their phenotype of; age of onset, type of seizures, and frequency of seizures. The data warrants a genetic study to be conducted on epilepsy and seizures in the breed. This should include a study of pedigrees, as well as inclusion in some of the molecular genetic studies on epilepsy presently being conducted in other breeds of dogs.
Hot Spots was tied for the third most frequent (8.37%) diagnosis, with 20 dogs recorded. Related diagnoses were Lick Sores (14, tied for 7=5.86%), Allergies (9, ranked 14=3.77%), and Flea Allergy (8, ranked 15=3.35%). These diagnoses were spread across all age groups. Some dogs were listed in more than one of these categories. All these categories relate to reactive or allergic skin disease, which is a frequent diagnosis in the general canine population. While this is a frequent occurrence, and there are many breeds with higher frequencies of these diagnoses, they are still considered a group of hereditary conditions that should be selected against. It is interesting that Chinook crosses had no diagnoses of hot spots, only one with lick sores, 2 with allergies, and 1 with flea allergies. It is possible that in some dogs, lick sores to their owners could actually be lick granulomas, which are considered a behavioral problem triggered by anxiety. If this is the case, it could be expected to find more diagnoses of lick sores in Chinook crosses, especially since their percentage of shyness diagnoses is greater than that in purebred Chinooks. There is no established mode of inheritance for these conditions. Chinook breeders should select against these disorders as polygenic traits.
Shyness was the fifth most frequent (7.95%) diagnosis with 19 dogs recorded. This is one of the few diagnoses where the frequency in Chinook crosses significantly exceeded that in purebred Chinooks. This behavior is uniformly recorded as occurring from birth, and includes notations of; “shy with strangers,” “timid of men,” “afraid of visitors,” “panics at loud noises,” “terrified of strangers,” “timid with strangers,” “hates strange places,” “hides,” “frightens easily,” and “hides with strangers.” In addition, the category of Temperament-Other contained one diagnosis of “Cautious,” which could have been included in the shyness category. The Chinook was not originally bred to be a social dog, but a working dog. If the breed wishes to establish the Chinook as a family dog, and can breed away from this temperament without losing its working ability, then it should recommend this to its breeders. Owners felt that this was enough of a problem to write these additional comments on the survey forms. The mode of inheritance of behavioral disorders has not been established.
Total Hip Dysplasia was the sixth most frequent (7.11%) diagnosis with 17 dogs recorded. Hip Dysplasia-Subluxation ranked 11, with 12 diagnoses (5.02%), and Hip Dysplasia-Other ranked 20, with 4 diagnoses (1.67%). There was one dog listed only with Hip Laxity. This is a category where it is possible the recorded frequency may be lower than the actual frequency. Unless all owners screened their dogs for hip dysplasia, many dogs may not show signs of the disorder until their later years. Some may never show signs, although their hip x-rays may show laxity, malformation or degeneration, and would pass on genes for these traits to their offspring. The frequency of Total Hip Dysplasia for Chinook crosses (8.45%) exceeds that of purebred Chinooks. This is unfortunate, as one objective of the cross program was to correct this problem. Hip dysplasia is not an uncommon diagnosis in large breeds of dogs, especially in those that share the Chinook body type. The crosses used, all have measurable frequencies of hip dysplasia in their purebred populations. This is a polygenic disorder, and is considered a threshold trait, although there may be major recessive or dominant genes influencing the disorder in some families. It is interesting that a breed such as the Chinook, which was selected almost exclusively for its working ability, would have a high frequency of hip dysplasia. Breeders should use breadth of pedigree when selecting against hip dysplasia.
Arthritis was tied as the seventh most frequent (5.86%) diagnosis with 14 dogs recorded. This is a symptom of degenerative skeletal disease, and probably reflects hip dysplasia, as well as other conditions causing secondary arthritis. Each has its own hereditary basis.
Difficulty Whelping is the tenth most frequent (5.36%) diagnosis, with 6 of 112 females recorded. Comments included; “uterine inertia,” “dystocia,” “hydrops puppy,” “fetal oversize and stillbirth,” “hydrops/C-section,” and “C-section.” As found with the litter analysis, the appearance of any hydrops pups in a breed is a confirmed genetic problem. As affected dogs cannot survive and reproduce, it must be considered that there are one or more major recessive genes at work. The heredity should be investigated, and breeders should select against carriers of the disorder.
CONCLUSIONS
The Chinook breed appears to be vigorous, and healthy. There does not appear to be any prenatal lethal recessives present in the breed, although there is a low frequency problem with hydrops/hydrocephalus. The major genetic disorders; Cryptorchidism, Hot Spots (allergic skin disease), Epilepsy (seizures), Shyness, and Hip Dysplasia are seen in many breeds, but are being seen at higher frequencies in purebred Chinooks. With the identification of these disorders as hereditary problems in the breed, owners can concentrate on selecting against them, while working to maintain form and function of the breed.
The breed must decide whether it wants to develop a conformational standard to create more uniformity in the breed. In doing so, breeders must recognize that dogs with superior conformation, function, and temperament should be selected from all family lines, to not limit existing genetic diversity. The breed also needs to determine the status of cross breeding programs. Many mushers crossbreed to produce their sled dogs, but do not consider them to be purebred, or seek to reintroduce offspring back into a purebred population. The breed needs to come to a decision on the advantages and disadvantages of introducing genes from other breeds into the Chinook gene pool. Based on the results of this study, and the Chinook Genetic Diversity Study, the breed has a large enough population to sustain itself, and does not exhibit symptoms of a lack of genetic diversity. The number and frequency of genetic disorders are not different from other rare breeds, who with breeder education and research, have achieved genetic improvement.
Jerold S. Bell, D.V.M.
Clinical Assistant Professor of Genetics
Department of Clinical Sciences
Tufts University School of Veterinary Medicine
North Grafton, Massachusetts
This cover report accompanies the data report on the Chinook Breed Health Survey. There was a good response rate to the survey, with 49.04% returning surveys. The majority of dogs still reside in Maine and the other New England states, although Chinook populations are growing in other areas of the country. The vast majority of respondents felt that canine hip dysplasia is the most important health problem facing the breed. A limited gene pool was also a concern, and will be addressed in the Chinook Genetic Diversity Study. Epilepsy and retained testicles (cryptorchidism) were also singled out as problems, and the concern for these three mentioned hereditary disorders is supported by the data.
Any survey such as this cannot attempt to identify the true frequency of disease or health in the breed. While the response rate is good based on registration figures, healthy dogs are under reported in most surveys. While this tends to overestimate the frequency of disorders in the breed, repeated diagnoses suggest problem areas. The relative frequency of diagnoses can be compared with each other to rank the prevalence or importance of disorders in the breed. The inclusion of Chinook cross data allows comparison, and provides important information on the frequency of diagnoses.
There is a large population of purebred Chinooks, with a large population of possible breeding (sexually intact) dogs. Chinooks appear to live a normal lifespan, and based on the age distribution, there is an increasing population. There is more variation in height and weight than found in many other breeds. This may relate to the fact that the breed was created from diverse origins based on working ability, and not a conformational standard. The colors, eye color, and ear set are similarly varied.
A smaller population of Chinook crosses is similarly long lived, with a young breeding population. The population represents the influence of several different breeds. The population shows averages similar to the purebred population, with variation in height, weight, color, eye color, and ear set.
Litters of purebred Chinooks do not show a decrease in litter size that might be expected with an inbred population. There was no significant difference in litter size between purebred and crossbred Chinooks. Stillborn puppies, not due to dystocia or uterine infection occurred at a frequency of 3.8%. This corresponds to one puppy per every four litters, which is slightly higher than the average canine population. There was a significant occurrence of hydrops or hydrocephalus puppies, with one occurring in four different litters between 1982 and 1996. Reports of birth defects were higher than canine averages, but included 9.7% of males with cryptorchidism. This was not considered a birth defect on the litter form, and will instead be addressed in the breed diagnoses. Without these dogs, an 8.6% frequency of birth defects remains high. Hydrops/hydrocephalus and umbilical hernia top the list with frequencies of 2.2% each. Color of puppies listed showed a significantly higher percentage of silver/gray dogs than that recorded in the adult population. From the Chinook cross litters, there was again a varied population, with only one stillborn puppy, and no birth defects recorded.
In the survey data of individual dog diagnoses, 41.8% of purebred Chinooks, and 59.2% of Chinook crosses had no disease listed. The frequency of diagnoses by category
mirrored the frequently diagnosed individual disorders contained within them. In compiling the list of specific disorders, three were added as combinations of separate diagnoses, based on our knowledge of the inheritance of these disorders. Cryptorchidism- Unilateral (11) and Cryptorchidism-Bilateral (7) were combined to Total Cryptorchidism. Hip Dysplasia-Subluxation (12), Hip Dysplasia-Other (4), and Hip Laxity (1) were combined to Total Hip Dysplasia, while ensuring that individual dogs were not listed in more than one category. Epilepsy or Hereditary Seizures (10) and Non-Epileptic Seizures (10) were combined to All Seizure Disorders, as these two diagnoses cannot be differentiated clinically.
DISCUSSION OF TOP TEN DIAGNOSES
Total Cryptorchidism topped the list of Chinook diagnoses with a startlingly high 14.63% of all male dogs affected. Cryptorchidism-Unilateral had 11 diagnoses to be the second most frequent (8.94%) diagnosis for the breed, and Cryptorchidism-Bilateral had 7 diagnoses to be the ninth most frequent (5.69%) diagnosis for the breed. Litter survey forms had 9.7% of male puppies with retained testicles, including some where all males in the litter were affected. Cryptorchidism is defined as the failure of one or both testicles to descend into the scrotum by eight weeks of age. The reported incidence of retained testicles in the general canine population is approximately 0.8%. Unilateral and bilateral retained testicles are caused by the same genetic process, as is delayed descent of the testicles into the scrotal sac (which was not surveyed for). It is known that this is a sex limited disorder (females cannot express the trait). Females, including dams and littermates of affected dogs, can be genetically affected and pass on the trait at the same frequency as affected males. The mode of inheritance of cryptorchidism has not been established. The fact that Chinook crosses also had a significantly high percentage of diagnoses may suggest a major dominant influence. Conversely, many experts feel that this may be a polygenic trait, where a threshold of genes must combine to produce the disorder. With the high prevalence of the disorder in purebred Chinooks, they may pass on enough defective genes to cause crossbred dogs (not necessarily first generation) to express the trait. A genetic study of the relationship of these dogs should be investigated, and more data should be collected on dogs with cryptorchidism, and those with late descending testicles. Even if these frequencies are overestimated, this is an alarmingly high number of diagnoses for a rare breed.
All Seizure Disorders was tied for the third most frequent (8.37%) diagnosis with 20 dogs recorded. Ten dogs were listed with Epilepsy (tied for 12=4.18%) and ten dogs were listed with Non-Epileptic Seizures (tied for 12=4.18%). The clinical descriptions of the seizure disorders in these two groups overlap, and could not be differentiated. The onset of seizures ranged from 9 weeks, to six years of age, with most between 9 months and four years of age. Six dogs had their first seizure at less than one year of age, seven dogs between one and three years of age, five dogs between three and five years of age, one at six years of age, and one with no age recorded. Most dogs had multiple seizures, but four of the twenty have had only one seizure recorded to date. Three of the twenty had multiple seizures over at least a one year period, but have not observed any since then. Chinook crosses had three dogs with seizures (4.23%); one that was eventually euthanized due to seizures, and two that had recurrent seizures, for one and four years duration, but none since then. The high frequency of Chinooks and Chinook crosses with seizures of any kind is significant. While it is not infrequent to see dogs with single seizures who never seize again, these are occurrences across all breed lines; not clustered within the same breed. Some genetic mechanism is causing Chinooks and Chinook crosses to have seizures at a much higher rate than the general canine population. Epilepsy is known to be a group of different genetic disorders, which must be separated based on their phenotype of; age of onset, type of seizures, and frequency of seizures. The data warrants a genetic study to be conducted on epilepsy and seizures in the breed. This should include a study of pedigrees, as well as inclusion in some of the molecular genetic studies on epilepsy presently being conducted in other breeds of dogs.
Hot Spots was tied for the third most frequent (8.37%) diagnosis, with 20 dogs recorded. Related diagnoses were Lick Sores (14, tied for 7=5.86%), Allergies (9, ranked 14=3.77%), and Flea Allergy (8, ranked 15=3.35%). These diagnoses were spread across all age groups. Some dogs were listed in more than one of these categories. All these categories relate to reactive or allergic skin disease, which is a frequent diagnosis in the general canine population. While this is a frequent occurrence, and there are many breeds with higher frequencies of these diagnoses, they are still considered a group of hereditary conditions that should be selected against. It is interesting that Chinook crosses had no diagnoses of hot spots, only one with lick sores, 2 with allergies, and 1 with flea allergies. It is possible that in some dogs, lick sores to their owners could actually be lick granulomas, which are considered a behavioral problem triggered by anxiety. If this is the case, it could be expected to find more diagnoses of lick sores in Chinook crosses, especially since their percentage of shyness diagnoses is greater than that in purebred Chinooks. There is no established mode of inheritance for these conditions. Chinook breeders should select against these disorders as polygenic traits.
Shyness was the fifth most frequent (7.95%) diagnosis with 19 dogs recorded. This is one of the few diagnoses where the frequency in Chinook crosses significantly exceeded that in purebred Chinooks. This behavior is uniformly recorded as occurring from birth, and includes notations of; “shy with strangers,” “timid of men,” “afraid of visitors,” “panics at loud noises,” “terrified of strangers,” “timid with strangers,” “hates strange places,” “hides,” “frightens easily,” and “hides with strangers.” In addition, the category of Temperament-Other contained one diagnosis of “Cautious,” which could have been included in the shyness category. The Chinook was not originally bred to be a social dog, but a working dog. If the breed wishes to establish the Chinook as a family dog, and can breed away from this temperament without losing its working ability, then it should recommend this to its breeders. Owners felt that this was enough of a problem to write these additional comments on the survey forms. The mode of inheritance of behavioral disorders has not been established.
Total Hip Dysplasia was the sixth most frequent (7.11%) diagnosis with 17 dogs recorded. Hip Dysplasia-Subluxation ranked 11, with 12 diagnoses (5.02%), and Hip Dysplasia-Other ranked 20, with 4 diagnoses (1.67%). There was one dog listed only with Hip Laxity. This is a category where it is possible the recorded frequency may be lower than the actual frequency. Unless all owners screened their dogs for hip dysplasia, many dogs may not show signs of the disorder until their later years. Some may never show signs, although their hip x-rays may show laxity, malformation or degeneration, and would pass on genes for these traits to their offspring. The frequency of Total Hip Dysplasia for Chinook crosses (8.45%) exceeds that of purebred Chinooks. This is unfortunate, as one objective of the cross program was to correct this problem. Hip dysplasia is not an uncommon diagnosis in large breeds of dogs, especially in those that share the Chinook body type. The crosses used, all have measurable frequencies of hip dysplasia in their purebred populations. This is a polygenic disorder, and is considered a threshold trait, although there may be major recessive or dominant genes influencing the disorder in some families. It is interesting that a breed such as the Chinook, which was selected almost exclusively for its working ability, would have a high frequency of hip dysplasia. Breeders should use breadth of pedigree when selecting against hip dysplasia.
Arthritis was tied as the seventh most frequent (5.86%) diagnosis with 14 dogs recorded. This is a symptom of degenerative skeletal disease, and probably reflects hip dysplasia, as well as other conditions causing secondary arthritis. Each has its own hereditary basis.
Difficulty Whelping is the tenth most frequent (5.36%) diagnosis, with 6 of 112 females recorded. Comments included; “uterine inertia,” “dystocia,” “hydrops puppy,” “fetal oversize and stillbirth,” “hydrops/C-section,” and “C-section.” As found with the litter analysis, the appearance of any hydrops pups in a breed is a confirmed genetic problem. As affected dogs cannot survive and reproduce, it must be considered that there are one or more major recessive genes at work. The heredity should be investigated, and breeders should select against carriers of the disorder.
CONCLUSIONS
The Chinook breed appears to be vigorous, and healthy. There does not appear to be any prenatal lethal recessives present in the breed, although there is a low frequency problem with hydrops/hydrocephalus. The major genetic disorders; Cryptorchidism, Hot Spots (allergic skin disease), Epilepsy (seizures), Shyness, and Hip Dysplasia are seen in many breeds, but are being seen at higher frequencies in purebred Chinooks. With the identification of these disorders as hereditary problems in the breed, owners can concentrate on selecting against them, while working to maintain form and function of the breed.
The breed must decide whether it wants to develop a conformational standard to create more uniformity in the breed. In doing so, breeders must recognize that dogs with superior conformation, function, and temperament should be selected from all family lines, to not limit existing genetic diversity. The breed also needs to determine the status of cross breeding programs. Many mushers crossbreed to produce their sled dogs, but do not consider them to be purebred, or seek to reintroduce offspring back into a purebred population. The breed needs to come to a decision on the advantages and disadvantages of introducing genes from other breeds into the Chinook gene pool. Based on the results of this study, and the Chinook Genetic Diversity Study, the breed has a large enough population to sustain itself, and does not exhibit symptoms of a lack of genetic diversity. The number and frequency of genetic disorders are not different from other rare breeds, who with breeder education and research, have achieved genetic improvement.