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- Author or Editor: Janyce L. Seahorn x
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Abstract
Objective
To determine the cardiopulmonary and sedative effects of medetomidine hydrochloride in adult horses and to compare those effects with effects of an equipotent dose of xylazine hydrochloride.
Animals
10 healthy adult female horses.
Procedure
5 horses were given medetomidine (4 μg/kg of body weight, IV), and the other 5 were given xylazine (0.4 mg/kg, IV). Heart rate, respiratory rate, arterial blood pressures, pulmonary arterial blood pressures, and cardiac output were recorded, and sedation and ataxia scores were assigned before and every 5 minutes after drug administration for 60 minutes. Rectal temperature and blood gas partial pressures were measured every 15 minutes after drug administration.
Results
Arterial blood pressure was significantly decreased throughout the study among horses given medetomidine and was significantly decreased for 40 minutes among horses given xylazine. Compared with baseline values, cardiac output was significantly decreased 10, 20, and 40 minutes after administration of medetomidine and significantly increased 40 and 60 minutes after administration of xylazine. Despite the significant decrease in respiratory rate in both groups, results of blood gas analyses were not significantly changed over time. Ataxia and sedation scores were of similar magnitude for the 2 groups, but ataxia persisted slightly longer among horses given medetomidine. Horses resumed eating hay 10 to 55 minutes after drug administration.
Conclusions and Clinical Relevance
Results suggest that equipotent low doses of medetomidine and xylazine induce comparable levels of ataxia and sedation and similar cardiopulmonary changes in adult horses. (Am J Vet Res 1999;60:1371–1376)
Abstract
Objective
To determine hemodynamic and metabolic effects of IV infusion of ATP-MgCl2 combination and maximal safe IV infusion rate in conscious horses.
Animals
6 adult female horses.
Procedure
All horses received an IV infusion of ATP-MgCl2 combination, beginning at a rate of 0.05 mg of ATP/kg of body weight/min, which was increased by 0.05 mg/kg/min increments at 10-minute intervals until a rate of 1.0 mg/kg/min was achieved. Data were collected prior to the start of the infusion, at the end of each infusion rate, and at 15-minute intervals for the next hour after discontinuation of the infusion. Measured or calculated hemodynamic variables included cardiac output, cardiac index, heart rate, stroke volume, systemic and pulmonary arterial pressures, and systemic and pulmonary vascular resistances. Arterial blood gas tensions, CBC, plasma biochemical profiles, urine volume and specific gravity, and selected clinical signs of disease also were evaluated.
Results
Intravenous infusion of ATP-MgCl2 significantly increased cardiac output, decreased systemic vascular resistance, and caused mild pulmonary hypertension. Magnitude of the hemodynamic alterations was dependent on rate of infusion. Maximal safe infusion rate for these horses was 0.3 mg/kg/min. All horses became lethargic, and their appetites diminished during the infusion; 5 horses had mild signs of abdominal discomfort. Flank sweating was observed in all horses as infusion rate increased. Urine volume and specific gravity and hematologic, biochemical, and arterial blood gas alterations were detected during and after infusion.
Conclusions and Clinical Relevance
Intravenous administration of ATP-MgCl2 in healthy, conscious, adult horses caused various metabolic and hemodynamic alterations that were without appreciable detrimental effects. (Am J Vet Res 1999;60:1140–1147)
Abstract
Objective
To quantify plasma and urine nitric oxide (NO) concentrations before and after low-dose endotoxin infusion in horses.
Animals
11 healthy adult female horses.
Procedure
Eight horses were given endotoxin (35 ng/kg of body weight, IV) over 30 minutes. Three sentinel horses received an equivalent volume of saline (0.9% NaCl) solution over the same time. Clinical signs of disease and hemodynamic variables were recorded, and urine and plasma samples were obtained to measure NO concentrations prior to endotoxin infusion (t = 0) and every hour until postinfusion hour (PIH) 6, then every 2 hours until PIH 24. Blood for hematologic and metabolic analyses and for serum cytokine bioassays were collected at 0 hour, every hour until PIH 6, every 2 hours through PIH 12, and finally, every 6 hours until PIH 24.
Results
Differences in plasma NO concentrations across time were not apparent, but urine NO concentrations significantly decreased at 4 and 20 to 24 hours in endotoxin-treated horses. Also in endotoxin-treated horses, alterations in clinical signs of disease, and hemodymanic, metabolic, and hematologic variables were significant and characteristic of endotoxemia. Serum interleukin-6 (IL-6) activity and tumor necrosis factor (TNF) concentrations were increased above baseline values from 1 to 8 hours and 1 to 2 hours, respectively.
Conclusions and Clinical Relevance
Plasma and urine NO concentrations did not increase in horses after administration of a low dose of endotoxin, despite induction of an inflammatory response, which was confirmed by increased TNF and IL-6 values characteristic alterations in clinical signs of disease, and hematologic, hemodynamic and metabolic variables. (Am J Vet Res 1999:60:969-976)
Abstract
Objective—To characterize the temporality of dates of breeding and abortion classified as mare reproductive loss syndrome (MRLS) among mares with abortions during early gestation.
Animals—2,314 mares confirmed pregnant at approximately 28 days after breeding from 36 farms in central Kentucky, including 515 mares that had earlyterm abortions.
Procedure—Farm veterinarians and managers were interviewed to obtain data for each mare that was known to be pregnant to determine pregnancy status, breeding date, last date known to be pregnant, and date of abortion.
Results—Mares bred prior to April 1, 2001, appeared to be at greatest risk of early-term abortion, both among and within individual farms. Mares bred in mid-February appeared to be at greatest risk of abortion, with an estimated weekly incidence rate of abortion of 66% (95% CI, 52% to 80%).
Conclusions and Clinical Relevance—Mares in central Kentucky bred between mid-February and early March were observed to be at greatest risk of early-term abortion, and risk gradually decreased to a background incidence of abortion of approximately 11%. Mares bred after April 1, 2001, appeared to be at markedly less risk, indicating that exposure to the cause of MRLS likely occurred prior to this date. (Am J Vet Res 2005;66:1792–1797)
Summary
During a 3½-year period, cardiac arrhythmias were identified in 6 of 67 horses diagnosed with duodenitis/proximal jejunitis (dpj). Arrhythmias were detected by auscultation of irregular cardiac rhythm and subsequently were characterized by electrocardiographic evaluation. Arrhythmias included frequent second-degree atrioventricular block, ventricular ectopic depolarizations, and atrioventricular conduction disturbance. In 4 horses, arrhythmias resolved with recovery from the primary problem. One horse died suddenly 66 hours after admission, and another was euthanatized at 72 hours after admission.
Clinical and laboratory data from horses with dpj and cardiac arrhythmias (group l) were compared with findings for horses with dpj and without arrhythmias (group 2). Group-1 horses had significantly (P <0.05) higher serum bicarbonate concentration and serum creatine kinase activity.
Normal sinus rhythm returned in all 4 group-1 horses that recovered from dpj, suggesting a causal relationship between dpj and the arrhythmias. Two group-1 horses were necropsied, and both had myocarditis. The cause of these lesions was not determined.
Abstract
Objective—To identify factors associated with abortions during early gestation classified as mare reproductive loss syndrome (MRLS).
Design—Case-control study.
Animals—324 broodmares from 43 farms in central Kentucky, including 121 mares from 25 farms that had early-term abortions (ETAs) associated with MRLS (case horses), 120 mares from the same farms but that did not abort, and 83 mares from 18 farms that were not severely impacted by MRLS.
Procedure—Farm managers were interviewed to obtain data on various management practices and environmental exposures for the mares. Data for case and control horses were compared to identify risk factors for mares having MRLS-associated ETAs.
Results—Several factors increased the risk of MRLS-associated ETAs, including feeding hay in pasture, greater than usual amounts of white clover in pastures, more eastern tent caterpillars in pastures, abortion during a previous pregnancy, and sighting deer or elk on the premises.
Conclusions and Clinical Relevance—Analysis indicates that certain characteristics of pastures predisposed mares to MRLS-associated ETAs. Methods for limiting exposure to pasture (keeping mares in stalls longer) during environmental conditions similar to those of 2001 (ie, sudden freezing in mid-April following warmer-than-usual springtime temperatures and larger-than-usual numbers of eastern tent caterpillars in and around pastures) should reduce the risk of mares having MRLS-associated ETAs. It was not possible to determine whether exposure to white clover or caterpillars were causal factors for MRLS or were merely indicators of unusual environmental conditions that resulted in exposure of mares to a toxic or infectious agent. (J Am Vet Med Assoc 2003;222:210–217)
Abstract
Objective—To identify factors significantly associated with an epidemic of fibrinous pericarditis during spring 2001 among horses in central Kentucky.
Design—Case-control study.
Animals—38 horses with fibrinous pericarditis and 30 control horses examined for other reasons.
Procedure—A questionnaire was developed to solicit information regarding a wide range of management practices and environmental exposures from farm owners or managers.
Results—The following factors were found in bivariate analyses to be significantly associated with an increased risk of pericarditis: being from a farm with mares and foals affected by mare reproductive loss syndrome, exposure to Eastern tent caterpillars in or around horse pastures, younger age, shorter duration of residence in Kentucky and at the farm of current residence, being fed hay grown outside Kentucky, a lack of access to pond water, access to orchard grass for grazing, and a lack of direct contact with cattle. In multivariate logistic regression analyses, only variables related to caterpillar exposure and age were significantly associated with fibrinous pericarditis.
Conclusions and Clinical Relevance—Results suggest that fibrinous pericarditis in horses may be associated with mare reproductive loss syndrome. Exposure to Eastern tent caterpillars was the greatest risk factor for development of fibrinous pericarditis. The distribution of times of diagnosis of fibrinous pericarditis was consistent with a point-source epidemic. (J Am Vet Med Assoc 2003;223:832–838)
Abstract
Objective—To identify factors associated with abortions of mares during late gestation attributed to mare reproductive loss syndrome (MRLS).
Design—Case-control study.
Animals—282 broodmares from 62 farms in central Kentucky, including 137 mares that had late-term abortions (LTAs) associated with MRLS, 98 mares from the same farms that did not abort, and 48 mares that aborted from causes other than MRLS.
Procedure—Farm managers were interviewed to obtain data on a wide range of management practices and environmental exposures for the mares. Data for case and control horses were compared to identify risk factors for a mare having a MRLS-associated LTA (MRLS-LTA).
Results—Several factors increased the risk of mares having MRLS-LTAs, including increased amount of time at pasture, less time in a stall, feeding concentrate on the ground, higher proportion of diet derived from grazing pasture, being fed in pasture exclusively during the 4-week period prior to abortion, access to pasture after midnight during the 4-week period prior to abortion, and drinking from a water trough or not having access to water buckets or automatic waterers.
Conclusions and Clinical Relevance—Analysis indicates that exposure to pasture predisposed mares to having MRLS-LTAs and stillborn foals. Methods for limiting exposure to pasture (keeping mares in stalls longer) during environmental conditions similar to those seen in 2001 should reduce the risk of mares having MRLS-LTAs. (J Am Vet Med Assoc 2003;222:199–209)