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There are definite physiological differences between breeds of dogs that are sometimes not recognized by the mainstream of veterinary thought. An example of this is the sensitivity of sighthounds and some other breeds to the traditional anesthetic regimens used for many years. Now it seems to be common knowledge in the veterinary community but I can remember back to a time (one that wasn't very long ago, by the way) where many veterinarians pooh-poohed the notion that a particular breed would have an unusually high proportion of adverse reactions to the ultra-fast acting barbiturates commonly used as preanesthetic agents. Mind you, many sighthound breeders and fanciers were acutely aware of this danger because of the abundant anecdotal evidence of dogs dying or having serious adverse reactions to anesthesia for routine procedures. In fact, some sighthound breeders and owners would bring articles from sighthound magazines about this phenomenon to their vets to try to alert them about this. And sometimes it worked and sometimes the vets would dismiss the information contemptuously because it did not come from traditional veterinary science journals. Since that time, mainstream research has been done on this and there have been veterinary articles published on the unusual reactions of Greyhounds to barbiturates. And now you are unlikely to get into an argument with your vet if you bring the subject up. In the last few years, I have heard a number of sighthound breeders (not just Greyhound breeders but those from other sighthound breeds as well) discuss the fact that they suspect that the "normal" range of values for thyroid function in other breeds may not be the same for sighthounds. In particular, there seem to be a lot of sighthounds who routinely test out as low-normal (meaning their thyroid values are considered normal but are in the bottom third of the 'normal' range). These dogs tend to be asymptomatic when judged against most typical symptoms of classic hypothyroidism. Their coats are not dry, their energy levels are appropriate for their breed and age, and (ex-track Greyhounds aside) they don't have bald patches. Racing Greyhounds have certain features of their living conditions and diet that are not similar to most other sighthounds. They live in crate kennels (where they are crated for a much larger proportion of the day than would be the average pet or show dog who is crated). Their weight is kept on the low side. The females are given mibolerone (Cheque) or testosterone, and these are hormones that affect both reproduction and other hormonal systems in the body. I also would consider a Greyhound racing kennel to be a more stressful environment than many others. Any one or a combination of these features (and others that I haven't listed) could be factors in both the much discussed bald patches that are often seen on the upper back of their thighs and in a (possibly transient) low or low-normal thyroid reading. I also wonder what the California vet who is finding 50% of the dogs hypothyroid is using as her guideline. Is she using the same guidelines of a T4 reading of 1-4 that is seen as 'normal' by the majority of vets, or is she counting low-normal dogs as being in the group of hypothyroid dogs? The fact that a dog coming off the track may have a low-normal thyroid reading would not be that significant to me unless there were symptoms that needed to be treated. By that I mean symptoms aside from a bald butt. I don't believe in treating a lab result, I believe in treating a whole animal. As I and others have previously noted, there are many dogs with 'bald butts' and normal thyroid readings. There are also many low thyroid dogs in the world without bare butts. (The alopecia caused by severe hypothyroidism tends to be more extensive than that, so that there is hair loss in many areas.) There is an old scientific adage: "Correlation is not causation." so just seeing dogs with bare butts who are hypothyroid also does not prove that the hypothyroidism caused the alopecia. They both may be caused by a single separate cause entirely, or they might even be unrelated. I did a search of Biological Abstracts, Medline, and Life Sciences Collection on canine thyroid problems and breed differences. One study did find that racing Greyhounds had lower thyroid levels. I've gotten the full survey on another which mentioned breeds with higher frequency of hypothyroidism but did not list Greyhounds or any other sighthound breed among them. I'm including some of the citations in case anyone is interested. Specifics of Endocrinal Pathology in Racing Greyhounds Bloomberg M-S Univ. Fla., Coll. Vet. Med., Gainesville, FL. 32610-0126, USA. RECL MED VET EC ALFORT 167 (7-8). 1991. 787-793. CODEN: RMVEA Full Journal Title: Recueil de Medecine Veterinaire de l'Ecole d'Alfort Language: FRENCH Among the endocrinal particularities to be found in racing greyhounds can be counted:
The author reviews the clinical aspects concerning these three elements. Descriptors/Keywords: STEROID ABUSE HYPOTHYROID PROBLEM INSIPID EFFORT-RELATED DIABETES Hypothyroidism in dogs: 66 cases (1987-1992) Sixty-six dogs with hypothyroidism were identified from dogs examined over a 5-year period. Hypothyroidism was diagnosed only if the dog had a low, resting serum thyroxine concentration and serum thyroxine concentration was not higher than the lower limits of the reference range 6 hours after IV administration of bovine thyrotropin. The prevalence of hypothyroidism was 0.2%. Neutering was determined to be the most significant gender-associated risk factor for development of hypothyroidism. Neutered male and spayed female dogs had a higher relative risk of developing hypothyroidism than did sexually intact females. Sexually intact females had a lower relative risk. Breeds with a significantly increased risk, compared with other breeds, were the Doberman Pinscher and Golden Retriever. The most common clinical findings were obesity (41%), seborrhea (39%), alopecia (26%), weakness (21%), lethargy (20%), bradycardia (14%), and pyoderma (11%). Low voltage R-waves were found on 58% of ECG. Clinicopathologic abnormalities included hypercholesterolemia (73%), nonregenerative anemia (32%), high serum alkaline phosphatase activity (30%), and high serum creatine kinase activity (18%). Serum total triiodothyronine concentrations were within reference ranges in 15% of the hypothyroid dogs. Response to treatment was good in most dogs, but those with severe concurrent disease or neurologic abnormalities were less likely to respond with complete resolution of clinical signs. Descriptors/Keywords: RESEARCH ARTICLE; PREVALENCE; TREATMENT Effects of Age Sex and Boby Size on Serum Concentrations of Thyroid and Adrenocortical Hormones In Dogs Thyroxine (T4), 3,5,3'-triiodothyronine (T3), and cortisol frequently are quantified in canine serum or plasma samples to aid in the diagnosis of hypothyroidism, hypoadrenocorticism, and hyperadrenocorticism. Many laboratories have established reliable references values for concentrations of these hormones in blood of clinically normal animals. However, nonpathologic factors that affect thyroidal and adrenocortical secretion may lead to misinterpretation of test results when values for individual animals are compared with reference values. The objective of the study reported here was to identify effects of age, sex, and body size (ie, breed) on serum concentrations of T3, T4, and cortisol in dogs. Blood samples were collected from 1,074 healthy dogs, and serum concentrations of the iodothyronines and cortisol were evaluated for effects of breed/size, sex, and age. Mean (.+-. SEM) serum concentration of T4 was greater in small (2.45 .+-. 0.06 .mu.g/dl)- than in medium (1.94 .+-.0.04 .mu.g/dl)- of all other ages, except middle-aged adults. Mean serum T3 concentration in medium-sized dogs (1.00 .+-. 0.01 ng/ml) was greater than that in small (0.90 .+-. 0.01 ng/ml)- and large (0.88 .+-. 0.01 ng/ml)-breed dogs. Serum T3 concentration was lowest in nursing (0.85 .+-. 0.01 ng/ml) and weanling (0.77 .+-. 0.02 ng/ml) pups, increased in rapidly growing dogs (0.99 .+-. 0.01 ng/ml) and young adult dogs (1.10 .+-. 0.04 ng/ml), and decreased slightly in middle-aged (0.98 .+-. 0.02 ng/ml) and old (1.01 .+-. 0.03 ng/ml) adult dogs. Serum T3 concentration was unaffected by sex. Mean serum cortisol concentration was greater in small (1.06 .+-. 0.07 .mu.g/dl)- than in large (0.79 .+-. 0.03 .mu.g/dl)-breed dogs. Serum from nursing pups (0.57 .+-. 0.04 .mu.g/dl) contained less cortisol than did serum from older dogs (mean values .gtoreq. 0.92 .mu.g/dl). Serum cortisol concentration was not different between males and females. These effects of breed/size and age on serum T3, T4, and cortisol concentrations should be considered when evaluating thyroid and adrenocortical functions in dogs. Descriptors/Keywords: HYPOADRENOCORTICISM HYPOTHYROIDISM HYPERADRENOCORTICISM THYROXINE 3 5 3' TRIIODOTHYRONINE CORTISOL DIAGNOSIS Plasma Concentrations of Thyroid Hormones in Dogs Influence of Sampling Hour Breed and Age Thyroxine (T4) and triiodothyronine (T3) plasma concentrations have been determined during 24-hr sampling periods in six mongrels (age 12-36 months), six beagles (age 35-37 months), three labradors (age 3.5 months) and three beagles (age 5 months). The mean T4 levels of the labradors were significantly lower than the values found for mongrels or older beagles (P Descriptors/Keywords: THYROXINE TRIIODOTHYRONINE Survey of Thyro Globulin Auto Antibodies in Dogs An enzyme-linked immunosorbent assay was used to detect autoantibodies to thyroglobulin in dogs with and without clinical evidence of thyroid disease. Autoantibodies were found in 59% of 34 clinically hypothyroid dogs, 43% of 65 dogs with nonthyroidal endocrine diseases, 47% of 64 healthy dogs closely related to antibody-positive canine hospital patients, and 13% of 1057 canine hospital patients without endocrine disorders. Dogs with bacterial skin disease and alopecia of unknown causes had an increased prevalence of autoantibodies compared with the prevalence of autoantibodies in healthy dogs and dogs with other diseases. Three breeds of dogs, Great Danes, Irish Setters and Old English Sheepdogs, had an increased occurrence of autoantibodies compared with that in other breeds and dogs of mixed breeding. A familial tendency to thyroid autoimmunity was demonstrated in a group of Great Dane dogs. The occurence of autoantibodies was not influenced by age or sex. Thyroid function, as assessed by total thyroxine estimation, was depressed in hospitalized dogs compared with the thyroid function in healthy dogs, irrespective of thyroglobulin - antibody status. Two of 11 autoantibody - positive dogs monitored for an 18-mo. period developed low thyroxine concentration and depressed thyroid responsiveness to exogenous thyrotropin stimulation. Descriptors/Keywords: GREAT DANE IRISH SETTER OLD ENGLISH SHEEP DOG THYROTROPIN HORMONE-DRUG THYROXINE HYPO THYROIDISM NONTHYROIDAL ENDOCRINE DISEASE BACTERIAL SKIN DISEASE FAMILIAL TENDENCY The Phase of Hair Growth in Hypo Thyroidism in the Dog The stage of hair growth which predominated in dogs not affected with hypothyroidism appeared to be breed-dependent. For example, in boxers, Labradors and collies, the resting stage (telogen) predominated, whereas in West Highland White terriers and cairn terriers the active stage (anagen) predominated. However, even in pet dogs kept mainly indoors, the proportion of hairs in anagen tended to increase during the winter months. In dogs affected with hypothyroidism, the proportion of hairs in anagen or telogen in members of a particular breed was the same as in the normal dogs of the breed. Breed apparently was more influential than hypothyroidism in determining the predominant phase of hair growth. Descriptors/Keywords: BOXER LABRADOR COLLIE WEST HIGHLAND WHITE TERRIER CAIRN TERRIER BREED DEPENDENCE Epidemiologic Features of Canine Hypo Thyroidism The epidemiologic features of 3206 dogs diagnosed with hypothyroidism (including myxedema) from 1.1 million dogs seen at 15 veterinary teaching hospitals between March, 1964 and June, 1978 were studied. Nine breeds at high-risk for hypothyroidism were golden retrievers, Doberman pinschers, dachshunds, Shetland sheepdogs, Irish setters, Pomeranians, miniature schnauzers, cocker spaniels and Airedales. Two breeds with a significant risk were German shepherds and mixed breed (mongrel) dogs. Age risk was greatest among younger dogs of high-risk breeds, further dogs had increasing relative risk through 9 yr of age. Spayed female dogs displayed a significantly higher risk when compared to intact females. Though not statistically significant, male castrated dogs had 30% more hypothyroidism compared to their intact counterparts. Among the case series were 91 endocrine and hormone - related neoplasms and 198 other endocrine-related disorders. Further studies linking canine hypothyroidism to other conditons, particularly cancer, could provide valuable insight into human disease experience. Descriptors/Keywords: GOLDEN RETRIEVER DOBERMAN PINSCHER DACHSHUND SHETLAND SHEEP DOG IRISH SETTER POMERANIAN MINIATURE SCHNAUZER COCKER SPANIEL AIREDALE GERMAN SHEPHERD HUMAN NEOPLASM AGE MYX EDEMA CASTRATION Hypo Thyroidism in Different Breeds The relationship between different breeds of dogs [Beagle, Sled Dog, Labrador, Retriever, Spaniel, Terrier, Collie, Mixed, Setter, Shepherd, Doberman, Poodle, Chihuahua, Dachshund and Schnauzer] and hypothyroidism is discussed. The results of 2000 tests for hypothyroidism are evaluated and presented in tabular form with breed relationships. The materials and methods utilized in the testing involved are described. The rationales for differing values by breed are discussed and the use of the testing program in practice is evaluated. Descriptors/Keywords: BEAGLE SLED DOG LABRADOR RETRIEVER SPANIEL TERRIER COLLIE MIXED SETTER SHEPHERD DOBERMAN POODLE CHIHUAHUA DACHSHUND SCHNAUZER Breed Differences and Similarities in Thyroid Function in Purebred Dogs Reproductive Manifestations of Thyroid Disease. Thyroid function and reproductive function have many interactions, the scope and mechanism of which are not fully understood. These functions are of greatest clinical importance for veterinarians working with breeders of purebred dogs. Thyroid dysfunction does not always result in clinical signs of reproductive disorders or in subfertility. It seems that animals with overt thyroid dysfunction are those most likely to manifest reproduction problems. (29 Refs.) Tags: Animal; Female; Male Canine Pseudohypothyroidism and Covert Hypothyroidism. Primary hypothyroidism is perhaps the most common endocrinopathy of the dog. Unfortunately, a paradox exists. Many cases of mild to moderately severe hypothyroidism are unrecognized, while many euthyroid dogs are misdiagnosed as having hypothyroidism. Uncommon manifestations resulting from earlier stages of primary hypothyroidism, from secondary/tertiary hypothyroidism, or from a unique interplay between thyroid hormone deficiency and the age, sex, or breed affected can obscure the clinical suspicion of hypothyroidism. Conversely, nonthyroidal diseases and drug therapy can alter thyroid hormone metabolism in ways that mimic hypothyroidism and can lead to an erroneous diagnosis. Misinterpretation of clinical signs and laboratory findings are also causes for an incorrect diagnosis of hypothyroidism. The level of confidence in the diagnosis of hypothyroidism should be reflected as "suspected," "probable," and "definitive" hypothyroidism. Screening laboratory evaluation should be serum T4 and free T4 levels. The most reliable current evaluation for equivocal cases is the thyroid - stimulating hormone (TSH) stimulation test. Intramuscular or subcutaneous administration of TSH provides a greater separation between normal and abnormal post-TSH response. A definitive diagnosis of hypothyroidism in an adult dog is a retrospective assessment based on complete recovery after appropriate thyroid hormone replacement. (87 Refs.) Tags: Animal Clinical and Histological Features of Primary Progressive, Familial Thyroiditis in a Colony of Borzoi dogs. A six-year study of clinical data and the morphologic changes involved in lymphocytic thyroiditis in a colony of related borzoi dogs was conducted. Lesions observed included initial degenerative thyroidal parenchymal changes which progressed to subacute inflammation with subsequent fibrosis and end stage thyroid gland disease. This study encompasses three successive generations of this borzoi colony and documents the progression of the histologic changes from the initial thyroid gland degenerative lesions to the end stage parenchymal atrophy. Spontaneous, familial thyroiditis has not been reported previously in the borzoi breed. Tags: Animal; Support, U.S. Gov't, P.H.S. |
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