Page 1388 - Small Animal Internal Medicine, 6th Edition

1360 PART XIII Hematology

CHAPTER 83
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Clinical Pathology

in Greyhounds and

Other Sighthounds

Since the early 1990s, more than 250,000 retired racing considered an adaptation to exercise, under selective breed-
Greyhounds (RRGs) have been placed in adoptive homes, ing for superior track performance, resulting in dogs with
and this number continues to increase each year. Practicing higher total oxygen-carrying capacity; however, numerous
veterinarians are facing an increasing number of Grey- studies are being done to further investigate the underlying
hounds for routine wellness examinations and medical and factors influencing these hematologic features in Grey-
surgical ailments. Consequently, they must be aware of the hounds. The macrocytosis historically reported in Grey-
unique hematologic and biochemical idiosyncrasies charac- hounds does not appear to be reproducible with current
teristic of the breed (Zaldívar-López et al., 2011a). instruments.
The Greyhounds’ history as racing sighthounds has Pretraining Greyhounds between 9 and 10 months of age
resulted in a unique physiology that distinguishes them from were found to already have higher HCT, Hb, and RBC values,
other breeds. Greyhounds have larger muscle mass than and a tendency toward higher MCV when compared with
most breeds; high hematocrit (HCT); lengthened carpal, non–breed-specific reference ranges (Shiel et al., 2007a). The
tarsal, metacarpal, and metatarsal bones; and a keen sense of selective breeding for speed in this breed is likely the cause
sight. These adaptations, among others, have likely contrib- of altered Hb function and properties because of the impera-
uted to the unique hematologic and biochemical character- tive need for an adequate oxygen supply at the tissue level
istics in Greyhounds compared with non-Greyhound breeds, under extreme conditions—that is, during the race (Zaldívar-
which have been well documented over the last 50 years. López et al., 2011b). Greyhounds have lower Hb P 50 values
Results of routine clinical pathology tests in RRGs frequently (the partial pressure of oxygen at which 50% of the Hb is
lie outside the reference ranges for dogs. Some of the hema- saturated) than non-Greyhounds. The oxyhemoglobin dis-
tologic peculiarities in Greyhounds have also been described sociation curve is left-shifted; thus the Greyhound’s Hb has
in other sighthounds. This chapter reviews clinicopathologic a higher affinity for oxygen than non-Greyhounds, despite
features specific to Greyhound dogs; these may also apply to similar concentrations of RBC 2,3-diphosphoglycerate
other sighthound breeds. We recently reported hematology (2,3-DPG; Sullivan et al., 1994). Therefore the high Hb and
and chemistry reference intervals (RIs) for Deerhounds HCT in Greyhounds may be a compensatory change second-
(please see Sheerer et al., 2013). ary to decreased oxygen delivery to the tissues (low P 50 ), as
seen in humans with high-affinity hemoglobinopathies. We
recently documented that Greyhound Hb has a few unique
HEMATOLOGY amino acid mutations relevant to the oxygen affinity proper-
ties, changing the position of the globin chains and “hoard-
Although many clinicopathologic differences between Grey- ing” oxygen (Bhatt et al., 2011). Unpublished molecular
hounds and other breeds have been investigated, most of the genetics studies of Greyhound Hb have confirmed this fact.
research has focused on differences in hematologic values in Excited or apprehensive Greyhounds frequently have a
the breed. Hematologic RIs for the breed have been pub- high HCT and reticulocyte count. We demonstrated that,
lished (Campora et al., 2011). immediately after a race, the HCT and reticulocyte count
increase proportionally for a brief period of time (60-90
ERYTHROCYTES minutes) (Horvath et al., 2014). This likely represents splenic
Previous studies have reported that Greyhounds have a release of reticulocytes in response to catecholamines.
higher HCT value and hemoglobin (Hb) concentration Interestingly, the dog erythrocyte antigen (DEA) distribu-
when compared with non-Greyhound dogs. Traditionally, tion is different in Greyhounds than in other breeds. In a
high HCT, Hb, and red blood cell (RBC) values have been recent study, only 13.3% of RRGs had DEA 1.1 antigen in

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