Objective—To determine pathophysiologic effects of phenylbutazone on the equine right dorsal colon (RDC).
Animals—12 healthy adult horses.
Procedures—A controlled crossover observational study was conducted. Clinical and serum variables, colonic inflammation (histologic grading), and measurement of myeloperoxidase (MPO) activity, malondialdehyde (MDA) and prostaglandin E2 (PGE2) concentrations, ingesta volatile fatty acid (VFA) content, and arterial blood flow in the RDC were evaluated for a 21-day period in horses administered phenylbutazone (8.8 mg/kg, PO, q 24 h) or a control substance.
Results—Data from 8 horses were analyzed. Plasma albumin concentrations decreased significantly from days 10 to 21 during phenylbutazone treatment, compared with results during the same days for the control treatment. Phenylbutazone treatment caused neutropenia (< 3.0 × 103 cells/μL). No other clinical or hematologic abnormalities were detected for phenylbutazone or control treatments. Two horses developed colitis while receiving phenylbutazone. No significant differences were detected in the RDC between phenylbutazone and control treatments for MPO activity, MDA and PGE2 concentrations, and histologic evidence of inflammation. Arterial blood flow in the RDC was significantly increased during phenylbutazone treatment, compared with values for the control treatment. Differences were identified in VFA production during phenylbutazone treatment, compared with the control treatment, with a decrease in acetic acid concentrations over time.
Conclusions and Clinical Relevance—Prolonged phenylbutazone administration caused hypoalbuminemia, neutropenia, changes in RDC arterial blood flow, and changes in VFA production. Veterinarians should monitor serum albumin concentrations and neutrophil counts and be cautious when making dosing recommendations for phenylbutazone treatment of horses.
Objective—To determine functional and morphologic
changes in palmar digital nerves after nonfocused
extracorporeal shock wave (ESW) treatment in horses.
Procedures—The medial and lateral palmar digital
nerves of the left forelimb were treated with nonfocused
ESWs. The medial palmar digital nerve of the
right forelimb served as a nontreated control nerve.
At 3, 7, and 35 days after treatment, respectively, 2
horses each were anesthetized and nerves were surgically
exposed. Sensory nerve conduction velocities
(SNCVs) of treated and control nerves were recorded,
after which palmar digital neurectomies were performed.
Morphologic changes in nerves were
assessed via transmission electron microscopy.
Results—Significantly lower SNCV in treated medial
and lateral nerves, compared with control nerves, was
found 3 and 7 days after treatment. A significantly lower
SNCV was detected in treated medial but not lateral
nerves 35 days after treatment. Transmission electron
microscopy of treated nerves revealed disruption of the
myelin sheath with no evidence of damage to Schwann
cell bodies or axons, 3, 7, and 35 days after treatment.
Conclusions and Clinical Relevance—Nonfocused
ESW treatment of the metacarpophalangeal area resulted
in lower SNCV in palmar digital nerves. This effect
likely contributes to the post-treatment analgesia
observed in horses and may result in altered peripheral
pain perception. Horses with preexisting lesions may be
at greater risk of sustaining catastrophic injuries when
exercised after treatment. (Am J Vet Res
Objective—To develop a quantitative method of interpreting tibial scintigrams of Thoroughbred racehorses with tibial stress fractures that may facilitate diagnosis of fractures and to provide prognostic information regarding future performance of affected horses.
Animals—35 Thoroughbred racehorses.
Procedures—Static bone-phase scintigrams of tibial stress fractures were quantitatively analyzed by use of ratios of the mean radionuclide counts per pixel in a region of interest (ROI) drawn around the area of increased uptake of radiopharmaceutical to mean counts per pixel in a second ROI drawn around an apparently normal area of the tibial diaphysis. In horses with unilateral fractures, ratios for the contralateral tibia were determined by use of 2 ROIs drawn at the same positions as the ROIs in the fractured tibia. Ratios were compared between fractured versus apparently normal tibias, between horses that returned to racing versus those that did not, and among horses with various grades of lameness. The association between ratios for fractured tibias and intervals between diagnosis and return to racing was also assessed.
Results—Mean ratio of ROIs in apparently normal tibias was 1.35 (95% confidence interval [CI], 1.21 to 1.50); that in tibias with stress fractures was 3.55 (95% CI, 2.50 to 4.60). These ratios were significantly different. None of the associations between ratios for fractured tibias and grades of lameness or performance outcomes were significant.
Conclusions and Clinical Relevance—Tibial stress fracture scintigrams can be quantitatively analyzed. A prospective study with a controlled rehabilitation period is necessary to evaluate the possible applications of this method.