Objectives—To acquire reference range values
indicative of glucose metabolism by use of the hyperglycemic
clamp technique in healthy horses and evaluate
the usefulness of the euglycemic hyperinsulinemic
clamp technique in healthy horses and ponies.
Animals—5 Dutch Warmblood horses and 4 Shetland
Procedure—The hyperglycemic clamp technique was
used for quantification of the sensitivity of beta cells
to exogenous glucose infusion in horses. The euglycemic
hyperinsulinemic clamp technique was used
to determine the sensitivity and responsiveness of
tissues to exogenous insulin in horses and ponies.
Results—During the hyperglycemic clamp technique,
the mean amount of glucose metabolized (M) in horses
was 0.011 ± 0.0045 mmol/kg·min–1 (95% confidence
interval [CI], 0.0018 to 0.020 mmol/kg·min–1;
range, 0.000035 to 0.021 mmol/kg·min–1) and the
mean M value-to-plasma insulin concentration (I) ratio
(ie, mmol of glucose/kg·min–1 per pmol of insulin/L X
100) was 0.017 ± 0.016 (95% CI, –0.014 to 0.049;
range, 0.000025 to 0.055). During the euglycemic
hyperinsulinemic clamp technique, the mean M value
was 0.014 ± 0.0055 mmol/kg·min–1 (95% CI, 0.0026 to
0.025 mmol/kg·min–1; range, 0.0042 to 0.023
mmol/kg·min–1) in horses and 0.0073 ± 0.0020
mmol/kg·min–1 (95% CI, 0.0034 to 0.011
mmol/kg·min–1; range, 0.0049 to 0.011 mmol/kg·min–1)
in ponies. The M value was significantly lower in
ponies than in horses, whereas the M:I ratios were
not significantly different between horses and ponies.
Conclusion and Clinical Relevance—Glucose clamp
techniques offer good methods to investigate glucose
metabolism in horses and ponies. A higher degree of
insulin resistance was found in ponies, compared with
Dutch Warmblood horses. (Am J Vet Res 2003;64: 1260–1264)
Objective—To determine the influence of age on
results of quantitative analysis of electromyographic
(EMG) needle examination in the subclavian, triceps,
and lateral vastus muscles of Dutch Warmblood horses.
Animals—7 healthy young Dutch Warmblood horses
(range, 13 to 18 months old), 7 healthy adult Dutch
Warmblood horses (range, 4 to 10 years old), and 7
healthy elderly Dutch Warmblood horses (range, 18 to
21 years old).
Procedure—An EMG needle examination was performed
to evaluate insertional activity, spontaneous
activity, and motor unit action potential (MUAP) variables.
Although all horses were conscious, young
horses were sedated prior to examination.
Results—Mean insertional activity in young horses
was significantly lower than in elderly horses.
Pathologic spontaneous activity was rarely found in
young and adult horses but was frequently evident in
all muscles in all elderly horses. The MUAP duration
and amplitude were significantly lower in all muscles
of young horses, compared with values for adult and
elderly horses. The MUAP duration and number of
phases and turns were significantly lower in adult
horses than in elderly horses. Group differences for
percentages of polyphasic and complex MUAPs were
also found. The 95% confidence intervals for MUAP
duration, MUAP amplitude, and number of phases
and turns for the subclavian, triceps, and lateral vastus
muscles were significantly lower in young horses
than in adult or elderly horses.
Conclusion and Clinical Relevance—Age of the
horse being examined should be considered when
EMG examination is performed. (Am J Vet Res
Objective—To compare the effects of administration of 2 volumes of a calcium solution (calcium oxide and calcium gluconate) on plasma ionized calcium concentration (PICaC) and clinical recovery from naturally occurring hypocalcemia (NOHC; milk fever) in lactating dairy cows.
Animals—123 cows with NOHC (PICaC < 0.95 mmol/L [3.81 mg/dL]) and 20 clinically normal control cows.
Procedures—Affected cows were treated IV once or repeatedly with 450 (n = 56) or 750 mL (67) of calcium solution (1.65 g of calcium/100 mL) until clinical recovery was achieved. The PICaC was assessed 48 hours after the first treatment or after the treatment that achieved clinical recovery. Biochemical recovery was defined as PICaC ≥ 0.95 mmol/L. Plasma from control cows was used for PICaC reference range determination. Plasma samples from both groups were assessed after storage for 20 days at 20°C.
Results—The PICaC reference range derived from blood collected in tubes containing lithium heparin was 1.02 to 1.29 mmol/L (4.09 to 5.17 mg/dL). Following storage, plasma samples were suitable for PICaC assessment. All cows treated with ≥ 1 volume of 450 and 750 mL of calcium solution recovered clinically; however, 31 of 83 (37%) evaluated cows were not biochemically recovered at 48 hours following treatment. Only cows with PICaC < 0.48 mmol/L (1.92 mg/dL) before the first treatment had to be treated ≥ 3 times.
Conclusions and Clinical Relevance—Results did not support the need to increase the administered volume of calcium solution from 450 to 750 mL for treatment of NOHC in dairy cows.
Objective—To compare the effects of IV administration of various doses of ovine corticotrophin–releasing hormone (oCRH) on plasma and saliva cortisol concentrations in healthy horses and determine whether an oCRH challenge test protocol is valid for use in adult horses.
Animals—24 healthy Warmblood horses.
Procedures—Each horse received oCRH in saline (0.9% NaCl) via IV administration at a dose of 0 (control treatment), 0.01, 0.1, or 1.0 Mg/kg (6 horses/group). Jugular blood and saliva samples were collected simultaneously 15 minutes before and immediately prior to injection (baseline); data from these samples were pooled to provide basal values. Subsequently, 14 postinjection blood and saliva samples were both collected within a 210-minute period. Cortisol concentrations in all samples were assessed via a solid-phase radioimmunoassay.
Results—All doses of oCRH induced significant increases from baseline in both plasma and salivary cortisol concentrations. Compared with the smaller doses of oCRH, the 1.0 Mg/kg dose of oCRH induced significantly greater plasma cortisol concentrations. A relationship (r = 0.518) between basal cortisol concentrations in plasma and saliva was detected.
Conclusions and Clinical Relevance—For use as a CRH challenge test in adult horses, a protocol involving IV administration of a dose of at least 0.01 Mg of oCRH/kg and postinjection collection of blood samples from 10 to 180 minutes and saliva samples from 20 to 50 minutes for assessment of plasma and saliva cortisol concentrations should be sufficient. Application of such a test might be helpful to detect states of chronic activation of the hypothalamo-pituitary-adrenocortical axis at the hypothalamic level.
Objective—To determine whether electromyographic
abnormalities are evident in skeletal muscles in
horses with induced hypocalcemia and hypomagnesemia.
Animals—7 healthy adult Dutch Warmblood horses.
Procedure—Electromyographic examination was
performed in the lateral vastus, triceps, and subclavian
muscles before and after IV infusion of EDTA. An
initial dose (mean ± SD, 564 ± 48 ml) of a 10% solution
of sodium EDTA was administered IV during a
period of 21 ± 7.3 minutes to establish a blood concentration
of ionized calcium of approximately 0.5
mMol/L. Average rate of EDTA infusion to maintain
ionized calcium at this concentration was 6.6 ml/min.
Results—Mean blood concentrations of ionized calcium
and magnesium were 1.39 ± 0.06 and 0.84 ± 0.09
mM, respectively before EDTA infusion; after EDTA
infusion, concentrations were 0.48 ± 0.05 and 0.44 ±
0.20 mM, respectively. This state induced positive
waves; fibrillation potentials; doublets, triplets, and
multiplets; complex repetitive discharges; and neuromyotonia.
Analysis of motor unit action potentials
(MUAP) after EDTA infusion revealed an increase in
prevalence of polyphasic and complex MUAP in all
Conclusion and Clinical Relevance—None of the
horses had classical signs of hypocalcemia and hypomagnesemia.
In contrast, all horses had spontaneous
activity in the measured muscles indicative of nerve
hyperirritability. Calcium and magnesium deficits
appear to have consequences, which may be subclinical,
affecting functions of the neuromuscular system.
This is of interest for equestrian sports in which
hypocalcemia and hypomagnesemia are expected,
such as during endurance rides. (Am J Vet Res
Objective—To evaluate the application of analysis of
motor unit action potentials (MUAP) in horses and to
obtain values of MUAP for the subclavian muscle of
Animals—10 healthy adult Dutch Warmblood horses.
Procedure—Electromyographic examination of the
subclavian muscle in conscious nonsedated horses
was performed to evaluate insertional activity, spontaneous
activity, MUAP variables, and recruitment
patterns. Muscle and body temperatures were measured
at the beginning and end of the procedure.
Amplitude, duration, number of phases, and number
of changes in direction (ie, turns) for all representative
MUAP were analyzed to determine values for this
muscle in this group of horses.
Results—Mean ± SD duration of insertional activity
was 471.7 ± 33.45 milliseconds. Mean MUAP amplitude
in the examined horses was 379 µV (95% confidence
interval [CI], 349 to 410 µV). Mean MUAP duration
of the subclavian muscle was 7.27 milliseconds
(95% CI, 6.84 to 7.71 milliseconds). Mean number of
phases was 2.9, and mean number of turns was 3.0.
Prevalence of polyphasic MUAP, defined as MUAP
with > 4 phases, was 7.7%. Number of MUAP that
had > 5 turns was 2.4%. Satellite potentials were
found in 1.0% of the MUAP.
Conclusions and Clinical Relevance—This study
revealed that electromyography including MUAP
analysis can be performed in horses, and values for
the subclavian muscle in healthy adult horses can be
obtained. Analysis of MUAP could be a valuable diagnostic
tool for use in discriminating between myogenic
and neurogenic problems in horses. (Am J Vet Res 2002;63:198–203)
Objective—To evaluate the effect of various head and neck positions on intrathoracic pressure and arterial oxygenation during exercise in horses.
Animals—7 healthy Dutch Warmblood riding horses.
Procedures—The horses were evaluated with the head and neck in the following predefined positions: position 1, free and unrestrained; position 2, neck raised with the bridge of the nose aligned vertically; position 4, neck lowered and extremely flexed with the nose pointing toward the pectoral muscles; position 5, neck raised and extended with the bridge of the nose in front of a vertical line perpendicular to the ground surface; and position 7, neck lowered and flexed with the nose pointing towards the carpus. The standard exercise protocol consisted of trotting for 10 minutes, cantering for 4 minutes, trotting again for 5 minutes, and walking for 5 minutes. An esophageal balloon catheter was used to indirectly measure intrathoracic pressure. Arterial blood samples were obtained for measurement of Pao2, Paco2, and arterial oxygen saturation.
Results—Compared with when horses were in the unrestrained position, inspiratory intrathoracic pressure became more negative during the first trot (all positions), canter and second trot (position 4), and walk (positions 4 and 5). Compared with when horses were in position 1, intrathoracic pressure difference increased in positions 4, 2, 7, and 5; Pao2 increased in position 5; and arterial oxygen saturation increased in positions 4 and 7.
Conclusions and Clinical Relevance—Position 4 was particularly influential on intrathoracic pressure during exercise in horses. The effects detected may have been caused by a dynamic upper airway obstruction and may be more profound in horses with upper airway disease.
Objective—To determine the influence of intensified training and subsequent reduced training on glucose metabolism rate and peripheral insulin sensitivity in horses and identify potential markers indicative of early overtraining.
Animals—12 Standardbred geldings.
Procedures—Horses underwent 4 phases of treadmill-based training. In phase 1, horses were habituated to the treadmill. In phase 2, endurance training was alternated with high-intensity exercise training. In phase 3, horses were divided into control and intensified training groups. In the intensified training group, training intensity, duration, and frequency were further increased via a protocol to induce overtraining; in the control group, these factors remained unaltered. In phase 4, training intensity was reduced. Standardized exercise tests were performed after each phase and hyperinsulinemic euglycemic clamp (HEC) tests were performed after phases 2, 3, and 4.
Results—10 of 12 horses completed the study. Dissociation between mean glucose metabolism rate and mean glucose metabolism rate-to-plasma insulin concentration ratio (M:I) was evident in the intensified training group during steady state of HEC testing after phases 3 and 4. After phase 4, mean glucose metabolism rate was significantly decreased (from 31.1 ± 6.8 μmol/kg/min to 18.1 ± 3.4 μmol/kg/min), as was M:I (from 1.05 ± 0.31 to 0.62 ± 0.17) during steady state in the intensified training group, compared with phase 3 values for the same horses.
Conclusions and Clinical Relevance—Dissociation between the glucose metabolism rate and M:I in horses that underwent intensified training may reflect non-insulin–dependent increases in glucose metabolism.
Objective—To confirm whether the plasma glucose
concentration curve obtained during oral glucose tolerance
tests (OGTTs) in horses with equine motor
neuron disease (EMND) is decreased, compared with
that obtained in clinically normal horses, and determine
whether that decrease is a result of defective
glucose metabolism or intestinal glucose transport
Animals—8 horses with EMND and 44 matched control
Procedure—Electromyography and OGTTs were performed
in all 8 affected horses and 10 control horses.
Intravenous GTTs (IVGTTs) were performed in 6
affected horses and another 11 control horses. The
activity and levels of jejunal luminal membrane glucose
transporter (Na+/glucose cotransporter isoform 1
[SGLT1]) were measured in 2 affected horses and 23
Results—In horses with EMND, generalized neuropathy
was detected via quantitative electromyography;
the mean increase in plasma glucose concentration
during the OGTT was significantly decreased,
compared with the value in control horses. During the
IVGTT, the mean increase in plasma glucose concentration
was significantly lower than that of control
horses. The activity and levels of SGLT1 in 2 affected
horses were similar to those of control horses.
Diagnosis of EMND was confirmed postmortem in all
Conclusions and Clinical Relevance—Data suggest
that the decreased plasma glucose curve obtained in
horses with EMND during OGTTs (compared with
control horses) is a result of overall enhanced glucose
metabolism or abnormalities in the facilitated glucose
transporters; definitive identification of the underlying
mechanisms could aid in the development of appropriate
treatments of EMND in horses. (Am J Vet Res 2005;66:93–99)
OBJECTIVE To determine effects of anesthesia on plasma concentrations and pulsatility of ACTH in samples obtained from the cavernous sinus and jugular vein of horses.
ANIMALS 6 clinically normal adult horses.
PROCEDURES Catheters were placed in a jugular vein and into the cavernous sinus via a superficial facial vein. The following morning (day 1), cavernous sinus blood samples were collected every 5 minutes for 1 hour (collection of first sample = time 0) and jugular venous blood samples were collected at 0, 30, and 60 minutes. On day 2, horses were sedated with xylazine hydrochloride and anesthesia was induced with propofol mixed with ketamine hydrochloride. Horses were positioned in dorsal recumbency. Anesthesia was maintained with isoflurane in oxygen and a continuous rate infusion of butorphanol tartrate. One hour after anesthesia was induced, the blood sample protocol was repeated. Plasma ACTH concentrations were quantified by use of a commercially available sandwich assay. Generalized estimating equations that controlled for horse and an expressly automated deconvolution algorithm were used to determine effects of anesthesia on plasma ACTH concentrations and pulsatility, respectively.
RESULTS Anesthesia significantly reduced the plasma ACTH concentration in blood samples collected from the cavernous sinus.
CONCLUSIONS AND CLINICAL RELEVANCE Mean plasma ACTH concentrations in samples collected from the cavernous sinus of anesthetized horses were reduced. Determining the success of partial ablation of the pituitary gland in situ for treatment of pituitary pars intermedia dysfunction may require that effects of anesthesia be included in interpretation of plasma ACTH concentrations in cavernous sinus blood.