Greyhounds and other sighthound breeds (e.g. Afghan hound, saluki, borzoi, Scottish deerhound, whippet) typically have basal levels of thyroid hormones at or even just below the lowest limits of the adult normal reference ranges for most other breeds. This situation has been largely overlooked, and is particularly noteworthy because of the relatively large numbers of retired racing greyhounds that are adopted as pets. The appropriate diagnosis of hypothyroidism in these dogs may be difficult to make, especially during the immediate post-adoption period when the animal may be in less than optimal health and is undergoing the stress of relocation and adjustment to a pet home. However, clinically evident hypothyroidism also exists in a subset of these dogs and is responsive to thyroid supplement. The dosage of replacement levothyroxine needed for hypothyroid sighthounds is typically about one-half of the twice-daily dosage given to other dog breeds (i.e. 0.1 mg per 20 lbs. body weight BID). Post-pill test levels should ideally be about or just below mid-range at 4-6 hours after the morning medication.

The clinical situation is complicated further by the common assumption that the pattern baldness ("bald thigh syndrome") commonly seen in adult greyhounds of racing stock background is caused by hypothyroidism or some other endocrine imbalance. The bald thigh presentation is a bilaterally symmetrical, nonpruritic alopecia of the caudal and lateral aspects of the thighs. Recent study of a large group of intact male and female racing greyhounds found no differences in the concentrations of thyroid hormones or testosterone between affected bald and unaffected control dogs, even though the racing females are routinely given testosterone injections to suppress estrus. Thus, the bald thigh syndrome of these dogs should not be attributed to hypothyroidism or testosterone levels.

Many retired or actively racing greyhounds have been exposed to a variety of tick-borne rickettsial organisms (Babesia canis, Babesia gibsoni, Ehrlichia canis, Ehrlichia platys, Rickettsia rickettsii). Adult racing and adopted former racers rarely show clinical signs of these diseases, but relatively often have low, moderate or even very high rickettsial antibody titers on serologic tests, indicating prior exposure to the organism(s). The most commonly seen antibody titers are to B. canis and E. canis. It has been estimated that as much as 70% of greyhound stock of the southern United States and Mexico will be babesia and/or ehrlichia antibody-positive. Many retired, adopted greyhounds are being screened for these diseases because of the common misperception among adoption groups that a positive serologic test for antibody equates with disease or disease risk. (The same well-meaning national effort also promotes thyroid testing and treatment of any greyhound with thyroid levels that appear below or at the lower end of the general reference ranges for dogs. This has lead to prescribing large overdoses of thyroid supplement in a futile attempt to increase blood thyroid levels to the expected therapeutic ranges for other breeds).

Greyhounds that remain healthy on physical examination and show no evidence of hemoparasites on thorough examination of the feathered edges of blood smears generally do not need to be treated for rickettsial diseases, especially babesiosis, on the face of mild to moderately high antibody titers. Although imidocarb diproprionate has recently become licensed for use in this country, it is expensive and can produce occasional, serious adverse reactions including death. It would be unwise, therefore, to treat asymptomatic antibody-positive dogs as a routine policy. If they are to participate in a blood donor program, however, they should be seronegative or have only low antibody titers (e.g. < 1:80 or 1:160 for babesia spp.; < 1:40 for ehrlichia or rickettsia spp.)

References: Beale, KM, Bloomberg, MS, Van Gilder, J. Wolfson, BB. Keisling, K. Correlation of racing and reproductive performance in greyhounds with response to thyroid function testing. J Am Anim Hosp Assoc 196: 263-269, 1991; Dodds, WJ. More information on hematologic characteristics of greyhounds. J Am Vet Med Assoc 206: 1312, 1995; Cowan, LA, Refsal, KR, Nachreiner, R., Schoning, P. Thyroid hormone and testosterone concentrations in racing greyhounds with and without bald thigh syndrome. J Vet Int Med 11(2):142, 1997.