Objective—To determine components of the
increase in oxygen consumption (O2) and evaluate
determinants of hemoglobin saturation (SO2) during
incremental treadmill exercise in unfit horses.
Animals—7 unfit adult mares.
Procedures—Horses performed 1 preliminary exercise
test (EXT) and 2 experimental EXT. Arterial and
mixed venous blood samples and hemodynamic measurements
were taken during the last 30 seconds of
each step of the GXT to measure PO2, hemoglobin
concentration ([Hb]), SO2, and determinants of acidbase
state (protein, electrolytes, and PCO2).
Results—Increased O2 during exercise was facilitated
by significant increases in cardiac output (CO),
[Hb], and widening of the arteriovenous difference in
O2. Arterial and venous pH, PaO2, and PvO2 decreased
during exercise. Arterial PCO2, bicarbonate ([HCO3−])a,
and [HCO3−]v decreased significantly, whereas PvCO2
and increased. Arterial and venous sodium concentration,
potassium concentration, strong ion difference,
and venous lactate concentration all increased significantly
Conclusions and Clinical Relevance—Increases in
CO, [Hb], and O2 extraction contributed equally to
increased O2 during exercise. Higher PCO2 did not
provide an independent contribution to shift in the
oxyhemoglobin dissociation curve (OCD) in venous
blood. However, lower PaCO2 shifted the curve leftward,
facilitating O2 loading. The shift of ODC resulted
in minimal effect on O2 extraction because of convergence
of the ODC at lower values of PO2.
Decreased pH appeared responsible for the rightward
shift of the ODC, which may be necessary to allow
maximal O2 extraction at high blood flows achieved
during exercise. (Am J Vet Res 2000;61:1325–1332)
Objective—To compare results of intradermal tests
(IDT), conducted using environmental allergens, in
horses without atopy and horses with chronic
obstructive pulmonary disease (COPD).
Animals—38 horses (22 horses without atopy and 16
horses with COPD).
Procedure—All horses were examined (physical
examination, hematologic examination, serum biochemical
analyses, examination of bronchoalveolar
lavage fluid). An IDT was conducted, using a full panel
of 73 allergens consisting of grasses, weeds, trees,
molds, and insects. Results of the IDT were evaluated
30 minutes and 4, 6, and 24 hours after injection
of allergens. Horses without atopy were euthanatized,
and gross and histologic changes of lung
parenchyma were assessed.
Results—Horses without atopy had a greater number
of positive immediate and late-phase reactions than
did horses with COPD. Horses with COPD did not
have a significantly greater number of positive reactions
than horses without atopy at any time period for
any allergen group (grasses, weeds, trees, molds,
Conclusions and Clinical Relevance—Positive
results of IDT document allergen-specific hypersensitivity
but do not necessarily distinguish clinically relevant
reactions from subclinical reactivity in horses
with COPD. Interpreting the clinical relevance of
results of IDT requires a thorough knowledge of the
medical history, physical examination findings, and
environment of each animal. (Am J Vet Res
Objective—To evaluate the diagnostic value of serum
concentrations of total magnesium (tMg) and ionized
magnesium (iMg), concentrations of magnesium
(Mg) in muscle, intracellular Mg (icMg) concentrations,
urinary Mg excretion (EMg), Mg clearance (CMg),
and fractional clearance of Mg (FCMg) in horses fed
diets with Mg content above and below National
Research Council recommendations.
Animals—9 young female horses.
Procedures—6 horses were fed a reduced-Mg diet
for 29 days followed by an Mg-supplemented diet for
24 days. Control horses (n = 3) were fed grass hay
exclusively. Blood, urine, and tissue samples were
collected, and an Mg retention test was performed
before and after restriction and supplementation of
Mg intake. Serum tMg, serum iMg, muscle Mg,
icMg, and urine Mg concentrations were measured,
and 24-hour EMg, CMg, and FCMg were calculated.
Results—Reductions in urinary 24-hour EMg, CMg, and
FCMg were evident after 13 days of feeding a reduced-Mg diet. Serum tMg and iMg concentrations, muscle
Mg content, and results of the Mg retention test
were not affected by feeding the Mg-deficient diet.
Spot urine sample FCMg accurately reflected FCMg calculated
from 6- and 24-hour pooled urine samples.
Mean ± SD FCtMg of horses eating grass hay was 29
± 8%, whereas mean FCtMg for horses fed a reduced-Mg diet for 29 days was 6 ± 3%.
Conclusions and Clinical Relevance—The 24-hour
EMg was the most sensitive indicator of reduced Mg
intake in horses. Spot sample FCMg can be conveniently
used to identify horses consuming a diet deficient
in Mg. (Am J Vet Res 2004;65:422–430)
Objectives—To determine effects of feeding diets
with various soluble-carbohydrate (CHO) content on
rates of muscle glycogen synthesis after exercise in
Animals—7 fit horses.
Procedures—In a 3-way crossover study, horses
received each of 3 isocaloric diets (a high soluble CHO
[HC] diet, a low soluble CHO [LC] diet, or a mixed soluble
CHO [MC] diet). For each diet, horses were subjected
to glycogen-depleting exercise, followed by feeding
of the HC, LC, or MC diet at 8-hour intervals for 72
Results—Feeding the HC diet resulted in a significantly
higher glycemic response for 72 hours and significantly
greater muscle glycogen concentration at 48 and
72 hours after exercise, compared with results after
feeding the MC and LC diets. Muscle glycogen concentrations
similar to baseline concentrations were
detected in samples obtained 72 hours after exercise in
horses when fed the HC diet. Rate of glycogen synthesis
was significantly higher when horses were fed
the HC diet, compared with values when horses were
fed the MC and LC diets. Glycogen synthase activity
was inversely related to glycogen content. Protein content
of glucose transporter-4 was the lowest at 72
hours after exercise when horses were fed the HC diet.
Conclusions and Clinical Relevance—Muscle glycogen
synthesis was slower after glycogen-depleting
exercise in horses, compared with synthesis in
humans. Feeding HC meals after strenuous exercise
hastened replenishment of muscle glycogen content,
compared with results for feeding of LC and MC
diets, by increasing availability of blood glucose to
skeletal muscles. (Am J Vet Res 2004;65:916–923)
Objective—To compare a radioallergosorbent test
and 2 ELISA with intradermal testing for the determination
of environmental allergen hypersensitivity in
horses with and without atopic diseases.
Design—Prospective clinical study.
Animals—10 horses with recurrent urticaria, 7 with
atopic dermatitis, 16 with chronic obstructive pulmonary
disease, and 22 without atopy.
Procedure—History, physical examination, hemogram,
serum biochemical analyses, bronchoalveolar
lavage, and an intradermal test (used as the criterion
standard) with a regional panel of 73 allergens were
performed in all horses. Serum was analyzed by use
of the 3 in vitro assays of allergen-specific IgE.
Results—An ELISA based on the α chain of the highaffinity
IgE receptor, the Fc∈ receptor immunoglobin ∈
chain (Fc∈RIα) for IgE, had the overall highest kappa
statistic (0.238), positive predictive value (49%), and
negative predictive value (78%). Overall agreement
between the Fc∈RIα-based ELISA and the intradermal
test was fair. The highest kappa statistic was obtained
by the Fc∈RIα-based ELISA in horses with atopic dermatitis
(0.330). Kappa statistics for the radioallergosorbent
test and a polyclonal antibody-based ELISA
agreed slightly with that of the intradermal test at best.
Conclusions and Clinical Relevance—None of the 3
serum allergy tests reliably detected allergen hypersensitivity,
compared with the intradermal test. The
Fc∈RIα-based ELISA performed significantly better
overall than the other 2 tests. Low sensitivity of all 3
assays indicates the need for continued study to elucidate
a more sensitive test for the determination of
potentially pathogenic allergens in horses. (J Am Vet
Med Assoc 2001;218:1314–1322)
Objective—To clone and sequence the cDNA for
feline preproparathyroid hormone (preproPTH) and to
compare that sequence with other known parathyroid
hormone (PTH) sequences.
Sample Population—Parathyroid glands from 1
Procedure—A cDNA library was constructed in λ
phage from feline parathyroid gland mRNA and
screened with a radiolabeled canine PTH probe.
Positive clones were sequenced, and nucleic acid and
deduced amino acid sequences were analyzed and
compared with known preproPTH and PTH
Result—Screening of approximately 2 X 105 recombinant
plaques revealed 3 that hybridized with the
canine PTH probe; 2 clones comprised the complete
sequence for feline preproPTH. Feline preproPTH
cDNA consisted of a 63-base pair (bp) 5'-untranslated
region (UTR), a 348-bp coding region, and a 326-bp 3'-UTR. The coding region encoded a 115-amino acid
peptide. Mature feline PTH consisted of 84 amino
acids. Amino acid sequence analysis revealed that
feline PTH was > 83% identical to canine, bovine,
swine, equine, human, and macaque PTH and 69, 71,
and 44% identical to mouse, rat, and chicken PTH,
respectively. Within the region responsible for hormonal
activity (amino acids 1 to 34), feline PTH was >
79% identical to other mammalian PTH sequences
and 64% identical to the chicken sequence.
Conclusions and Clinical Relevance—The amino
acid sequence of PTH is conserved among mammalian
species. Knowledge of the cDNA sequence
for feline PTH may be useful to investigate disturbances
of calcium metabolism and alterations in PTH
expression in cats. (Am J Vet Res 2002;63:194–197)
Objective—To evaluate calcium balance and parathyroid
gland function in healthy horses and horses with
enterocolitis and compare results of an immunochemiluminometric
assay (ICMA) with those of an
immunoradiometric assay (IRMA) for determination of
serum intact parathyroid hormone (PTH) concentrations
Animals—64 horses with enterocolitis and 62 healthy
Procedures—Blood and urine samples were collected
for determination of serum total calcium, ionized calcium
(Ca2+) and magnesium (Mg2+), phosphorus, BUN,
total protein, creatinine, albumin, and PTH concentrations,
venous blood gases, and fractional urinary clearance
of calcium (FCa) and phosphorus (FP). Serum
concentrations of PTH were measured in 40 horses by
use of both the IRMA and ICMA.
Results—Most (48/64; 75%) horses with enterocolitis
had decreased serum total calcium, Ca2+, and Mg2+
concentrations and increased phosphorus concentrations,
compared with healthy horses. Serum PTH concentration
was increased in most (36/51; 70.6%) horses
with hypocalcemia. In addition, FCa was significantly
decreased and FP significantly increased in
horses with enterocolitis, compared with healthy horses.
Results of ICMA were in agreement with results of
Conclusions and Clinical Relevance—Enterocolitis
in horses is often associated with hypocalcemia;
79.7% of affected horses had ionized hypocalcemia.
Because FCa was low, it is unlikely that renal calcium
loss was the cause of hypocalcemia. Serum PTH concentrations
varied in horses with enterocolitis and concomitant
hypocalcemia. However, we believe low PTH
concentration in some hypocalcemic horses may be
the result of impaired parathyroid gland function. ( Am
J Vet Res 2001;62:938–947)
Case Description—A 2-year-old Thoroughbred filly was evaluated because of hemorrhage from the vulva and suspected hematuria of 5 days' duration.
Clinical Findings—A primary coagulopathy was ruled out on the basis of results of hematologic testing. Vaginoscopy and cystoscopy revealed a large bleeding mass in the bladder that extended into the vagina, causing marked obliteration of normal urogenital structures and difficulty in urination. Histologic examination of endoscopic and surgical biopsy speci-mens revealed a poorly differentiated neoplasia likely of mesenchymal origin. Chronic suppurative cystitis caused by Streptococcus zooepidemicus was also diagnosed.
Treatment and Outcome—The tumor continued to grow despite treatment with doxorubicin and, within 45 days, was causing substantial discomfort and stranguria. Given the grave prognosis, the horse was euthanized. At necropsy, the tumor was found to have caused widespread destruction of the urinary bladder and to have invaded the broad ligament of the uterus. The mass was identified as a poorly differentiated leiomyosarcoma on the basis of results of histologic examination and immunohistochemical staining for α-actin.
Clinical Relevance—Findings suggested that leiomyosarcoma should be considered in the differential diagnosis when examining horses with urogenital bleeding.
Objective—To determine effects of experimentally induced hypercalcemia on serum concentrations and urinary excretion of electrolytes, especially ionized magnesium (iMg), in healthy horses.
Animals—21 clinically normal mares.
Procedures—Horses were assigned to 5 experimental protocols (1, hypercalcemia induced with calcium gluconate; 2, hypercalcemia induced with calcium chloride; 3, infusion with dextrose solution; 4, infusion with sodium gluconate; and 5, infusion with saline [0.9% NaCl] solution). Hypercalcemia was induced for 2 hours. Dextrose, sodium gluconate, and saline solution were infused for 2 hours. Blood samples were collected to measure serum concentrations of electrolytes, creatinine, parathyroid hormone, and insulin. Urine samples were collected to determine the fractional excretion of ionized calcium (iCa), iMg, sodium, phosphate, potassium, and chloride.
Results—Hypercalcemia induced by administration of calcium gluconate or calcium chloride decreased serum iMg, potassium, and parathyroid hormone concentrations; increased phosphate concentration; and had no effect on sodium, chloride, and insulin concentrations. Hypercalcemia increased urinary excretion of iCa, iMg, sodium, phosphate, potassium, and chloride; increased urine output; and decreased urine osmolality and specific gravity. Dextrose administration increased serum insulin; decreased iMg, potassium, and phosphate concentrations; and decreased urinary excretion of iMg. Sodium gluconate increased the excretion of iCa, sodium, and potassium.
Conclusions and Clinical Relevance—Hypercalcemia resulted in hypomagnesemia, hypokalemia, and hyperphosphatemia; increased urinary excretion of calcium, magnesium, potassium, sodium, phosphate, and chloride; and induced diuresis. This study has clinical implications because hypercalcemia and excessive administration of calcium have the potential to increase urinary excretion of electrolytes, especially iMg, and induce volume depletion.