SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
Use of routine hematologic testing in the evaluation of poor performance may,
therefore, be best restricted to the identification of obvious abnormalities, such as
marked anemia, leukocytosis, leukopenia, or hyperfibrinogenemia. These changes
are not diagnostic, but may substantiate the history that the horse is unwell.
LEUCOCYTE NUMBERS
No differences have been noted in the normal ranges of white blood cell (WBC)
numbers or differential leucocyte counts when values for horses receiving regular
training or work are compared with those of their sedentary counterparts.
Furthermore, neither endurance nor high intensity racetrack training produce any
significant changes in the leukogram. Exercise will, however, induce a temporary
influx of WBC's and may change the differential leukogram. More neutrophils and
lymphocytes (of splenic origin) enter the circulating pool. This influx of cells may not
be reflected in the WBC count due to the simultaneous mobilization of erythrocytes
and increase in circulating blood volume. Intensity of exercise is an important factor
in determining whether the leucocyte response will be detected. Immediately
following maximal exercise like racing, there may be no apparent change in WBC
numbers, or else a mild increase in conjunction with a transient lymphocytosis. Such
changes frequently cause a significant drop in the neutrophil to lymphocyte ratio.
These alterations are usually short-lived and succeeded by neutrophilia, apparent
leucocytosis and an increase in the N:L ratio. Such changes develop over a number
of hours after racing or a strenuous workout, and are believed due to the increases
in plasma cortisol concentration which are associated with this level of exertion.
While lymphocyte numbers decrease from the immediate post-exercise number,
lymphopenia is unusual as numbers rarely drop below those seen on the resting
leukogram.
In contrast, prolonged endurance exercise is associated with the development of a
pronounced leucocytosis and neutrophilia which frequently persists for up to 24
hours. Such changes are also indicative of prolonged stress and increased
adrenocorticoid secretion. The more fatigued the horses, the more pronounced the
stress leukogram. Exhausted endurance horses have similar leukocyte counts to
their less tired counterparts, but showed a pronounced left shift in neutrophil type.
One study of such horses found the mean differential to include 8% band cells, and 2
horses had 22% band cells. Calculation of the N:L ratio may be one means of
assessing the severity of stress (or distress) experienced by a horse, a value of
greater than 10 being compatible with approaching exhaustion.
PLASMA PROTEIN CONCENTRATION
Serum total protein concentrations of healthy equine athletes consistently fall in a
relatively narrow range (6.0-7.8 g/dl). Of this, albumin usually makes up about 50%,
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