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in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Summary

Medical records for 64 Thoroughbred and 45 Standardbred horses with osteochondrosis dissecans (ocd) of the tarsocrural joint that were treated by means of arthroscopic removal of the fragments before 2 years of age and before beginning racing were reviewed. Lesion site was recorded for all horses. The other foals from the dams of these surgically treated horses (siblings) were identified from mare progeny records. Racing data, including number of starts and money won during the 2- and 3-year-old racing years were obtained from the Jockey Club and the United States Trotting Association for affected horses and their siblings. Statistical analysis was performed to test the hypothesis that there was no difference between the racing performance of horses with ocd of the tarsocrural joint that were surgically treated by means of arthroscopic removal of the fragments prior to racing and that of their siblings.

One hundred and seventy-four lesions were recorded in 109 horses. The distribution of lesions was similar to that previously reported. For the Standardbreds, 22% of those that had surgery raced as 2 year olds and 43% raced as 3 year olds, compared with 42 and 50% of the siblings that raced as 2 year olds and 3 year olds, respectively. For the Thoroughbreds, 43% of those that had surgery raced as 2 year olds and 78% raced as 3 year olds, compared with 48% and 73% of the siblings that raced as 2 year olds and 3 year olds, respectively. The median number of starts for surgically treated horses was decreased, compared with median number of starts for siblings, for all groups except 3-year-old Thoroughbreds. The distribution of starts was different between surgically treated and sibling horses only for 2-year-old Standardbreds. Median earnings were lower for affected horses than for siblings for both breeds and both age groups. Among affected horses, ability to start at least 1 race was not associated with lesion location or unilateral vs bilateral involvement. There was a tendency for horses with multiple lesions to be less likely to start a race than horses with only a single lesion; however, the difference was significant only for 2-year-old Standardbreds. Affected Standardbreds and Thoroughbreds were less likely to race as 2 year olds than were their siblings.

Free access
in Journal of the American Veterinary Medical Association

Summary

Effects of low-flow ischemia and reperfusion of the large colon on systemic and colonic hemodynamic and metabolic variables were determined in horses. Twenty-four adult horses were randomly allocated to 3 groups: sham-operated (n = 6), 6 hours of ischemia (n = 9), and 3 hours of ischemia and 3 hours of reperfusion (n = 9). Low-flow ischemia was induced in groups 2 and 3 by reducing colonic arterial blood flow to 20% of baseline. Heart rate, arterial blood pressures, cardiac index, pulmonary artery pressure, right atrial pressure, and colonic blood flow were monitored. Arterial, mixed-venous, and colonic venous blood gas and oximetry analyses; PCV; and blood lactate and pyruvate and plasma total protein concentrations were measured. Data were recorded, and blood samples were collected at baseline and at 30-minute intervals for 6 hours; additionally, data were collected at 185, 190, and 195 minutes (corresponding to 5, 10, and 15 minutes of reperfusion in group-3 horses). There were no differences among groups at baseline or across time for any systemic hemodynamic or metabolic variable. Colonic blood flow did not change across time in group-1 horses. Colonic blood flow significantly (P < 0.05) decreased to 20% of baseline at induction of ischemia in horses of groups 2 and 3 and remained significantly decreased throughout the ischemic period in horses of groups 2 (6 hours) and 3 (3 hours). Colonic blood flow significantly (P < 0.05) increased above baseline by 5 minutes of reperfusion in group-3 horses. Colonic oxygen delivery and oxygen consumption, and colonic venous pH, Po2 percentage saturation of hemoglobin, and oxygen content were significantly (P < 0.05) decreased within 30 minutes after induction of ischemia in horses of groups 2 and 3; colonic venous Po2 colonic oxygen extraction ratio, and lactate and pyruvate concentrations were significantiy (P < 0.05) increased by 30 minutes of ischemia. These alterations continued throughout ischemia, but within 5 minutes of reperfusion in group-3 horses, these variables either returned to baseline (pH, Pco2 lactate, pyruvate), significantly (P < 0.05) increased above baseline (Po2 oxygen content, % saturation of hemoglobin), or significantly (P < 0.05) decreased below baseline (colonic oxygen extraction ratio). Colonic oxygen consumption remained decreased during reperfusion in group-3 horses. Colonic mucosal ischemia-reperfusion injury observed in this model of ischemia was associated with local colonic hemodynamic and metabolic alterations in the presence of systemic hemodynamic and metabolic stability. Reactive hyperemia was observed at restoration of colonic blood flow in group-3 horses and persisted during reperfusion. Colonic venous metabolic alterations were corrected at reperfusion, indicating adaptation of the colon to the return of blood flow and oxygen delivery with resultant decrease in anaerobic metabolism. The early alterations in these variables may simply represent a washout of metabolic by-products.

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in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of a tongue-tie on upper airway mechanics in clinically normal horses exercising on a treadmill following sternothyrohyoid myectomy.

Animals—6 Standardbreds.

Procedure—Upper airway mechanics were measured with horses exercising on a treadmill at 5, 8, and 10 m/s 4 weeks after a sternothyrohyoid myectomy was performed. Pharyngeal and tracheal inspiratory and expiratory pressures were measured by use of transnasal pharyngeal and tracheal catheters connected to differential pressure transducers. Horses were fitted with a facemask and airflow was measured by use of a pneumotachograph. Horses underwent a standardized exercise protocol on a treadmill at 5, 8, and 10 m/s with and without a tongue-tie in a randomized cross-over design. Inspiratory and expiratory airflow, tracheal pressure, and pharyngeal pressure were measured, and inspiratory and expiratory resistances were calculated.

Results—We were unable to detect an effect of a tongue-tie on any of the respiratory variables measured.

Conclusions and Clinical Relevance—Results indicate that a tongue-tie does not alter upper airway mechanics following sternothyrohyoid myectomy in clinically normal horses during exercise. (Am J Vet Res 2001;62:779–782)

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in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association

Abstract

Objective

To investigate the effect of a mask and pneumotachograph on ventilation, respiratory frequency, and tracheal and nasopharyngeal pressures in horses running on a treadmill.

Design

Six horses ran at 50, 75, and 100% of the speed that resulted in maximum oxygen consumption, with and without a mask and pneumotachograph. Tracheal and pharyngeal inspiratory and expiratory pressures, respiratory frequency, and arterial blood gases were measured.

Animals

Six Standardbred horses.

Procedure

Oxygen consumption was measured during an incremental exercise test to determine the speed that resulted in maximal oxygen consumption for each horse. Tracheal and pharyngeal pressures were measured, using transnasal tracheal and pharyngeal side-hole catheters connected to differential pressure transducers. Carotid arterial blood samples were collected and PaO2 , PaCO2 , and pH were measured with a blood gas analyzer.

Results

Peak tracheal and pharyngeal inspiratory pressures were significantly more negative, peak tracheal and pharyngeal expiratory pressures were significantly more positive and respiratory frequency was significantly lower (all P < 0.05) at all speeds when horses wore a mask The PaCO2 , was higher and arterial pH and PaO2 , were lower (P < 0.05) when horses wore a mask.

Conclusions

The mask and pneumotachograph altered upper airway pressures, respiratory frequency, and ventilation in horses running on a treadmill.(Am J Vet Res 1996; 57: 250-253)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To investigate the effect of combined staphylectomy and laryngotomy on upper airway mechanics in clinically normal horses running on a treadmill.

Animals

6 Standardbreds.

Procedure

Upper airway mechanics were measured with horses trotting or pacing on a treadmill at 5, 8, and 10 m/s before and 6 weeks after combined staphylectomy and laryngotomy. Pharyngeal and tracheal inspiratory and expiratory pressure were measured by use of transnasal tracheal and pharyngeal side hole catheters connected to differential pressure transducers. A pneumotachograph mounted on the rostral end of an airtight face mask was used to measure airflow.

Results

Upper airway and translaryngeal inspiratory impedances were higher, respiratory rate was decreased, and inspiratory time was longer (P < 0.05) at all speeds after staphylectomy and laryngotomy.

Conclusion

Combined staphylectomy and laryngotomy significantly affects upper airway mechanics in clinically normal horses.

Clinical Relevance

Because combined staphylectomy and laryngotomy exerts a potentially adverse effect on upper airway mechanics in clinically normal horses, the procedure should only be performed when it is clearly indicated. (Am J Vet Res 1997;58:1018–1021)

Free access
in American Journal of Veterinary Research

SUMMARY

Thirty horses were randomly assigned to 1 of 5 groups. All horses were anesthetized and subjected to ventral midline celiotomy, then the large colon was exteriorized and instrumented. Colonic arterial blood flow was reduced to 20% of baseline (bl) and was maintained for 3 hours. Colonic blood flow was then restored, and the colon was reperfused for an additional 3 hours. One of 5 drug solutions was administered via the jugular vein 30 minutes prior to colonic reperfusion: group 1, 0.9% NaCl; group 2, dimethyl sulfoxide: 1 g/kg of body weight; group 3, allopurinol: 25 mg/kg; group 4, 21-aminosteroid U-74389G: 10 mg/kg; and group 5, manganese chloride (MnCl2): 10 mg/kg. Hemodynamic variables were monitored and recorded at 30-minutes intervals. Systemic arterial, systemic venous (sv), and colonic venous (cv) blood samples were collected for measurement of blood gas tensions, oximetry, lactate concentration, Pcv, and plasma total protein concentration. The eicosanoids, 6-keto prostaglandin F, prostaglandin E2 and thromboxane B2, were measured in cv blood, and endotoxin was measured in cv and sv blood. Full-thickness biopsy specimens were harvested from the left ventral colon for histologic evaluation and determination of wet weight-to-dry weight ratios (WW:DW). Data were analyzed, using two-way ANOVA for repeated measures, and statistical significance was set at P < 0.05. Heart rate, mean arterial pressure, and cardiac output increased with MnCl2 infusion; heart rate and cardiac output remained increased throughout the study, but mean arterial pressure returned to bl values within 30 minutes after completion of MnCI2 infusion. Other drug-induced changes were not significant. There were significant increases in mean pulmonary artery and mean right atrial pressures at 2 and 2.5 hours in horses of all groups, but other changes across time or differences among groups were not observed. Mean pulmonary artery pressure remained increased through 6 hours in all groups, but mean right atrial pressure had returned to bl values at 3 hours. Mean colonic arterial pressure was significantly decreased at 30 minutes of ischemia and remained decreased through 6 hours; however, by 3.25 hours it was significantly higher than the value at 3 hours of ischemia. Colonic arterial resistance decreased during ischemia and remained decreased throughout reperfusion in all groups; there were no differences among groups for colonic arterial resistance. Colonic venous Po2, oxygen content, and pH decreased, and Pco2 and lactate concentration increased during ischemia but returned to bl values during reperfusion. Compared with bl values, colonic oxygen extraction ratio was increased from 0.5 to 3 hours. By 15 minutes of reperfusion, colonic oxygen extraction ratio had decreased from the bl value in all groups and either remained decreased or returned to values not different from bl through 6 hours. Colonic venous 6-keto prostaglandin F and prostaglandin E2 concentrations increased during ischemia, but returned to bl on reperfusion; there were no changes in thrombox- ane2 concentration among or within groups. Endotoxin was not detected in cv or sv blood after ischemia or reperfusion. There were no differences among or within groups for these variables. Low-flow ischemia and reperfusion (i-r) of the large colon caused mucosal injury, as evidenced by increases in percentage of surface mucosal disruption, percentage depth of mucosal loss, mucosal hemorrhage, mucosal edema, mucosal interstitial-to-crypt ratio, mucosal neutrophil index, submucosal venular neutrophil numbers, and mucosal cellular debris index. There was a trend (P = 0.06) toward greater percentage depth of mucosal loss at 6 hours in horses treated with dimethyl sulfoxide, compared with the vehicle control solution. There were no differences in the remainder of the histologic variables among groups. Full-thickness and mucosal WW:DW increased with colonic I-R, but there were no differences among groups. There was a trend (P = 0.09) toward neutrophil accumulation, as measured by myeloperoxidase activity, in the lungs after colonic I-R, but there were no differences among groups. There was no change in lung WW:DW after colonic I-R. There were no beneficial effects of drugs directed against oxygen-derived free radical-mediated damage on colonic mucosal injury associated with low-flow I-R. Deleterious drug-induced hemodynamic effects were not observed in this study.

Free access
in American Journal of Veterinary Research

SUMMARY

Twenty-four horses were randomly allocated to 3 groups. Horses were anesthetized, subjected to a ventral midline celiotomy, and the large colon was exteriorized and instrumented. Group-1 horses served as sham-operated controls. Group-2 horses were subjected to 6 hours of low-flow colonic arterial ischemia, and group-3 horses were subjected to 3 hours of ischemia and 3 hours of reperfusion. Baseline (bl) samples were collected, then low-flow ischemia was induced by reducing ventral colonic arterial blood flow to 20% of bl. All horses were monitored for 6 hours after bl data were collected. blood samples were collected from the colonic vein and main pulmonary artery (systemic venous [sv]) for measurement of plasma endotoxin, 6-keto prostaglandin F (6-kPG), thromboxane B2 (txb 2), and prostaglandin E2 (pge 2) concentrations. Tumor necrosis factor and interleukin-6 activities were measured in colonic venous (cv) serum samples. Data were analyzed, using two-way anova, and post-hoc comparisons were made, using Dunnett's and Tu- key's tests. Statistical significance was set at P < 0.05. Endotoxin was not detected in CV or sv plasma at any time. There was no detectable tumor necrosis factor or interleukin-6 activity in CV samples at any time. There were no differences at bl among groups for CV or sv 6-kPG, pge 2, or txb 2 concentrations, nor were there any changes across time in group-1 horses. Colonic venous 6-kPG concentration increased during ischemia in horses of groups 2 and 3; CV 6-kPG concentration peaked at 3 hours in group-3 horses, then decreased during reperfusion, but remained increased through 6 hours in group-2 horses. Systemic venous 6-kPG concentration increased during reperfusion in group-3 horses, but there were no changes in group- 2 horses. Colonic venous pge 2 concentration increased during ischemia in horses of groups 2 and 3, and remained increased for the first hour of reperfusion in group-3 horses and for the 6-hour duration of ischemia in group-2 horses. There were no temporal alterations in sv pge 2 concentration. There was no difference in CV or sv ixb2 concentration among or within groups across time; however, there was a trend (P = 0.075) toward greater CV txb 2 concentration at 3.25 hours, compared with bl, in group-3 horses. Eicosanoid concentrations were significantly lower in sv, compared with CV plasma. Prostaglandin E2 and 6-kPG concentrations were approximately 3 to 8 and 5 to 10 times greater, respectively, in CV than in sv plasma. The increased concentrations of 6-kPG and pge 2 in CV plasma were likely attributable to their accumulation secondary to colonic ischemia. The increased values of these vasodilator eicosanoids may have a role in the reactive hyperemia observed during reperfusion. The increased 6-kPG concentration in sv plasma may represent spillover from the colonic vasculature, but more likely reflects systemic production.

Free access
in American Journal of Veterinary Research