Objective—To determine effects of cyclophotocoagulation
via administration of 100 J with a neodymium:
yttrium aluminum garnet (Nd:YAG) laser on
corneal touch threshold (CTT), intraocular pressure
(IOP), aqueous tear production, and corneal nerve
morphology in eyes of dogs.
Procedure—Noncontact Nd:YAG laser was transsclerally
applied (10 applications; 25 W for 0.1 seconds for
each application to each of 4 quadrants) to the ciliary
body of the left eye of 15 dogs; the right eye was the
control eye. Corneal integrity, CTT, tear production as
measured by the Schirmer tear test (STT), and IOP were
evaluated for 14 days following laser treatment. On day
14, dogs were euthanatized, eyes harvested, and
corneas stained with gold chloride. Major nerve bundles
were analyzed by use of a drawing tube attached to a
light microscope, and maximum diameters were measured
by use of image analysis software.
Results—All laser-treated eyes had significantly higher
CTT values, compared with control eyes. Six of 15
laser-treated eyes developed ulcerative keratitis. On
most days, IOP was significantly lower in laser-treated
eyes in both morning and evening. Laser-treated
eyes had a significant decrease of approximately 1
nerve bundle/corneal quadrant. Values for STT or
nerve bundle diameters did not differ significantly.
Conclusion and Clinical Relevance—Administration
of 100 J with a Nd:YAG laser effectively
reduced IOP while increasing CTT and caused a significant
decrease in number, but not diameter, of
major corneal nerve bundles. Nerve damage and
corneal hypoesthesia are etiologic factors in ulcerative
keratitis following Nd:YAG cyclophotocoagulation.
(Am J Vet Res 2002;63:906–915)
Objective—To assess changes in systemic hydration,
concentrations of plasma electrolytes, hydration and
physical properties of colonic contents and feces, and
gastrointestinal transit in horses with access to large
amounts of grain.
Animals—6 horses with right dorsal colon (RDC) fistulas.
Procedure—In a crossover design, horses were alternately
fed 1 of 3 diets: orchard grass hay ad libitum
after being adapted to this diet for at least 5 days,
orchard grass hay ad libitum and 4.55 kg of grain
offered every 12 hours after being adapted to orchard
grass hay ad libitum for at least 5 days, or orchard grass
hay ad libitum and 4.55 kg of grain offered every 12
hours after being adapted to this diet for at least 5 days.
Physical examinations were performed and samples of
blood, colonic contents, and feces were collected
every 6 hours during a 48-hour observation period.
Results—Grain ingestion had several effects, including
changes in the concentrations of electrolytes in plasma;
RDC contents became more homogenous, dehydrated,
foamy, and less dense; RDC contents flowed
spontaneously when the cannula was opened; RDC
contents expanded when heated in an oven; and feces
became fetid and less formed. Horses did not have any
clinical signs of colic, endotoxemia, or laminitis.
Conclusions and Clinical Relevance—Changes
observed in the colonic contents and feces may be
explained by the large amounts of hydrolyzable carbohydrates
provided by grain. Access to large
amounts of grain may increase the risk of tympany
and displacement of the large intestine. ( Am J Vet Res 2004;65:687–694)
Objective—To assess changes in systemic hydration,
concentrations of electrolytes in plasma, hydration of
colonic contents and feces, and gastrointestinal transit
in horses treated with IV fluid therapy or enteral
administration of magnesium sulfate (MgSO4), sodium
sulfate (NaSO4), water, or a balanced electrolyte
Animals—7 horses with fistulas in the right dorsal
Procedure—In a crossover design, horses alternately
received 1 of 6 treatments: no treatment (control); IV
fluid therapy with lactated Ringer's solution; or enteral
administration of MgSO4, Na2SO4, water, or a balanced
electrolyte solution via nasogastric intubation.
Physical examinations were performed and samples
of blood, RDC contents, and feces were collected
every 6 hours during the 48 hour-observation period.
Horses were muzzled for the initial 24 hours but had
access to water ad libitum. Horses had access to hay,
salt, and water ad libitum for the last 24 hours.
Results—Enteral administration of a balanced electrolyte
solution and Na2SO4 were the best treatments
for promoting hydration of RDC contents, followed by
water. Sodium sulfate was the best treatment for promoting
fecal hydration, followed by MgSO4 and the
balanced electrolyte solution. Sodium sulfate caused
hypocalcemia and hypernatremia, and water caused
Conclusions and Clinical Relevance—Enteral
administration of a balanced electrolyte solution promoted
hydration of RDC contents and may be useful
in horses with large colon impactions. Enteral administration
of either Na2SO4 or water may promote
hydration of RDC contents but can cause severe electrolyte
imbalances. (Am J Vet Res 2004;65:695–704)
Objective—To determine whether a limited sampling time method based on serum iohexol clearance (Cliohexol) would yield estimates of glomerular filtration rate (GFR) in clinically normal horses similar to those for plasma creatinine clearance (Clcreatinine).
Animals—10 clinically normal adult horses.
Procedures—A bolus of iohexol (150 mg/kg) was administered IV, and serum samples were obtained 5, 20, 40, 60, 120, 240, and 360 minutes after injection. Urinary clearance of exogenous creatinine was measured during three 20-minute periods. The GFR determined by use of serum Cliohexol and plasma Clcreatinine was compared with limits of agreement plots.
Results—Values obtained for plasma Clcreatinine ranged from 1.68 to 2.69 mL/min/kg (mean, 2.11 mL/min/kg). Mean serum Cliohexol was 2.38 mL/min/kg (range, 1.95 to 3.33 mL/min/kg). Limits of agreement plots indicated good agreement between the methods.
Conclusions and Clinical Relevance—Use of serum Cliohexol yielded estimates of GFR in clinically normal adult horses similar to those for plasma Clcreatinine. This study was the first step in the evaluation of the use of serum Cliohexol for estimating GFR in adult horses.
Case Description—A 7-month-old 16.6-kg (36.5-lb) sexually intact female Golden Retriever was evaluated because of progressive severe bilateral membranous conjunctivitis, oral lesions, nasal discharge, and cough.
Clinical Findings—Histologic examination of conjunctival biopsy specimens revealed findings consistent with ligneous conjunctivitis. Circulating plasminogen activity was repeatedly low, and congenital plasminogen deficiency was identified as the underlying cause of the ocular, oral, and respiratory lesions.
Treatment and Outcome—Topical and subconjunctival administrations of fresh frozen plasma (FFP), topical administration of cyclosporine, and oral administration of azathioprine had no effect on the conjunctival membranes. Excision of the membranes followed by intensive treatment with topical applications of heparin, tissue plasminogen activator, corticosteroid, and FFP and IV administration of FFP prevented membrane regrowth. Intravenous administration of FFP increased plasma plasminogen activity to within reference limits, improved respiratory and oral lesions, and resulted in weight gain; discontinuation of this treatment resulted in weight loss, signs of depression, and worsening of lesions. After euthanasia because of disease progression, necropsy findings included mild hydrocephalus; multifocal intestinal hemorrhages; and fibrinous plaques in the oral cavity, nasopharynx, trachea, esophagus, and pericardium. Microscopically, the plaques were composed of fibrin and poorly organized granulation tissue. Fibrin thrombi were present within vessels in the lungs, oral cavity, and trachea.
Clinical Relevance—In dogs, congenital plasminogen deficiency can occur and may be the underlying cause of ligneous conjunctivitis. A combination of surgical and medical treatments may improve conjunctival membranes, and administration of FFP IV appears to be effective in treating nonocular signs of plasminogen deficiency.
Objective—To evaluate the precision of intradermal
testing (IDT) in horses.
Animals—12 healthy adult horses.
Procedure—IDT was performed on the neck of each
horse by use of 2 positive control substances (histamine
and phytohemagglutinin [PHA]) and a negative
control substance. An equal volume (0.1 mL) for each
injection was prepared to yield a total of 20 syringes
([4 concentrations of each positive control substance
plus 1 negative control substance] times 2 positive
control substances times 2 duplicative tests) for each
side of the neck. Both sides of the neck were used for
IDT; therefore, 40 syringes were prepared for each
horse. Hair was clipped on both sides of the neck, and
ID injections were performed. Diameter of the skin
wheals was recorded 0.5, 4, and 24 hours after ID
Results—Intra- and interhorse skin reactions to ID
injection of histamine and PHA resulted in wheals of
uniform size at 0.5 and 4 hours, respectively.
Significant intra- and interhorse variation was detected
in wheals caused by PHA at 24 hours.
Conclusions and Clinical Relevance—ID injection of
histamine and PHA caused repeatable and precise
results at 0.5 and 4 hours, respectively.
Concentrations of 0.005 mg of histamine/mL and
0.1 mg of PHA/mL are recommended for use as positive
control substances for IDT in horses. This information
suggests that consistent wheal size is evident
for ID injection of control substances, and variation in
wheals in response to ID injection of test antigens
results from a horse's immune response to specific
antigens. (Am J Vet Res 2005;66:1341–1347)
Objective—To evaluate differences in response to ID
injection of histamine, phytohemagglutinin (PHA), and
Aspergillus organisms between clinically normal horses
and horses with recurrent airway obstruction
Animals—5 healthy adult horses and 5 adult horses
Procedure—Intradermal testing (IDT) was performed
on the neck with 2 positive control substances (histamine
and PHA) and a mixture comprising 5
Aspergillus species. Four concentrations of each test
substance plus a negative control substance were
used. Equal volumes (0.1 mL) of each test substance
were prepared to yield 15 syringes ([4 concentrations
of each test substance plus 1 negative control substance]
times 3 test substances) for each side of each
horse (ie, 30 syringes/horse). Intradermal injections
were administered; diameter of wheals was recorded
0.5, 4, and 24 hours after injection.
Results—Hypersensitive responses to ID injection of
histamine were detected 0.5 hours after injection, and
a delay in wheal formation after ID injection of
Aspergillus mixture 24 hours after injection was detected
in RAO-affected horses but was not observed in clinically
normal horses. No differences were detected
between the 2 groups after ID injection of PHA.
Conclusions and Clinical Relevance—RAO-affected
horses are hypersensitive to histamine, suggesting that
RAO is associated with a heightened vascular response
to histamine. Higher concentrations of Aspergillus mixture
may be needed to detect horses that are sensitive
to this group of antigens. Wheal reactions to Aspergillus
may be a delayed response, suggesting that IDT results
should be evaluated 0.5, 4, and 24 hours after ID injection.
(Am J Vet Res2005;66:1348–1355)
Objective—To determine whether pharmacokinetic
analysis of data derived from a single IV dose of
iohexol could be used to predict creatinine clearance
and evaluate simplified methods for predicting serum
clearance of iohexol with data derived from 2 or 3
blood samples in clinically normal foals.
Animals—10 healthy foals.
Procedure—Serum disposition of iohexol and exogenous
creatinine clearance was determined simultaneously
in each foal (5 males and 5 females). A 3-compartment
model of iohexol serum disposition was
selected via standard methods. Iohexol clearance calculated
from the model was compared with creatinine
clearance. Separate limited-sample models were
created with various combinations of sample times
from the terminal slope of the plasma versus time
profile for iohexol. Correction factors were determined
for the limited-sample models, and iohexol
clearance calculated via each method was compared
with exogenous creatinine clearance by use of
method comparison techniques.
Results—Mean exogenous creatinine clearance was
2.17 mL/min/kg. The disposition of iohexol was best
described by a 3-compartment open model. Mean
clearance value for iohexol was 2.15 mL/min/kg and
was not significantly different from mean creatinine
clearance. A method for predicting serum iohexol
clearance based on a 2-sample protocol (3- and 4-hour
samples) was developed.
Conclusions and Clinical Relevance—Iohexol clearance
can be used to predict exogenous creatinine
clearance and can be determined from 2 blood samples
taken after IV injection of iohexol. Appropriate
correction factors for adult horses and horses with
abnormal glomerular filtration rate need to be determined.
(Am J Vet Res 2003;64:1486–1490)