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- Author or Editor: Antonio Cruz x
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Objective—To quantify changes in hoof wall strain distribution associated with exercise and time in Standardbreds.
Animals—18 young adult Standardbreds.
Procedures—9 horses were exercised 4 d/wk for 30 to 45 minutes at a medium trot for 4 months; 9 nonexercised horses served as the control group. Rosette strain gauges were used to measure the principal surface strains at the toe, lateral quarter of the hoof wall (LQ), and medial quarter of the hoof wall (MQ) of the right forefoot at the beginning and end of the experiment. Midstance maximal (msϵ1) and minimal (msϵ2) principal and peak minimal principal (pkϵ2) surface strains were measured; SDs of each of those variables were also calculated. Results were compared through ANOVA of time and exercise effects between and within the groups.
Results—Both the exercised and nonexercised groups had changes in strain distribution in their hooves over time. The msϵ1 did not change significantly with exercise; however, it changed significantly in both groups at both hoof quarters over time. At the beginning of the study, mean msϵ2 and pkϵ2 values were significantly higher in the exercised group than in the control group at the MQ and LQ but not at the toe. At the end of the study, these values were significantly higher in the control group than in the exercised group at the toe but not at the MQ or LQ.
Conclusions and Clinical Relevance—Detected changes in hoof wall surface strain may indicate the ability of hoof capsule material to respond to exercise. A better understanding of hoof adaptation to applied forces may allow implementation of proper trimming and shoeing techniques to promote adaptation to exercise loads in horses.
Objective—To study osteoarthritis in the equine medial femorotibial (MFT) joint after a single traumatic injury.
Animals—10 mature horses.
Procedure—In vitro explant cultures were used to determine injury threshold for stifle joint cartilage. Contusive impacts were applied to the medial femoral condyle (MFC), and horses were followed for 84 (n = 5) and 180 days (5). Synovial fluid samples were collected every 14 days for determination of sulphated glycosaminoglycan (sGAG) concentrations. Radiographic and lameness evaluations were performed. Gross and histologic descriptions, and immunohistochemistry, cartilage sGAG content determination, and cartilage aggregate modulus determination were performed at the MFC impact site (MFCi), MFC nonimpact site (MFCn), and medial tibial plateau (MTP).
Results—Synovial fluid sGAG concentration decreased significantly on days 14, 28, 42, and 56 in all horses. Macroscopic and microscopic articular lesions developed within all MFT joints. No radiographic abnormalities were observed. Mild lameness was evident in several horses. No significant differences were found between short-term and longterm cohorts of horses with respect to histologic scores and TUNEL results. On immunohistochemistry, MFCi was positive for COL2–¾Cshort. International Cartilage Repair Society scores differed significantly between short-term and long-term cohorts of horses. In all horses, sGAG concentrations were significantly decreased at the MFCi, compared with the MFCn.
Conclusions and Clinical Relevance—Use of contusive impacts on the MFC of horses results in cartilage lesions that are similar to those described clinically, supporting trauma as a contributing factor in the natural pathogenesis of osteoarthritis.
Objective—To determine the effects of indwelling nasogastric intubation on the gastric emptying rate of liquid in horses.
Animals—6 healthy horses.
Procedures—Horses were assigned to treatment and control groups in a prospective randomized crossover study with a washout period of at least 4 weeks between trials. Acetaminophen (20 mg/kg) diluted in 1 L of distilled water was administered via nasogastric tube at time points of 0, 12, 30, 48, and 72 hours to evaluate the liquid-phase gastric emptying rate. In control horses, nasogastric tubes were removed after administration of acetaminophen. In horses receiving treatment, the tube was left indwelling and maintained for 72 hours. A 10-mL sample of blood was collected from a jugular vein immediately before and 20, 40, 60, 80, 100, 120, and 180 minutes after acetaminophen administration. Serum acetaminophen concentrations were measured by use of a colorimetric method.
Results—Peak serum acetaminophen concentration was significantly higher in the control group (38.11 μg/mL) than in the treatment group (29.09 μg/mL), and the time required to reach peak serum acetaminophen concentration was significantly shorter in the control group (22.79 minutes) than in the treatment group (35.95 minutes).
Conclusions and Clinical Relevance—Results indicated that indwelling nasogastric intubation has a delaying effect on the gastric emptying rate of liquids. Veterinarians should consider the potential for delayed gastric emptying when placing and maintaining an indwelling nasogastric tube for an extended period of time after surgery. Repeated nasogastric intubation may be better than maintenance of an indwelling tube in horses with ileus.
Objective—To determine the anisotropic characteristics of the microarchitecture of the subchondral bone (SCB) plate and trabecular bone (TBB) of the distopalmar aspect of the metacarpal condyles in horses with different stages of SCB disease.
Sample Population—12 third metacarpal bone pairs from racing Thoroughbreds euthanized for diverse reasons.
Procedures—Both metacarpi were collected from horses with SCB changes that were mild (sclerosis and focal radiolucencies; n = 6) or severe (multifocal radiolucencies and articular surface defects; 6). Sample blocks of SCB plate and TBB were collected from the distopalmar aspect of both condyles and the sagittal ridge and examined via 3-D micro-computed tomography at 45-?m isotropic voxel resolution. For each sample, the angle between the principal orientation of trabeculae and the sagittal plane and the degree of anisotropy (DA) were calculated from mean intercept length measurements.
Results—Condylar samples had significantly lower angle (mean, 8.9°; range, 73° to 10.9°) than sagittal ridge samples (mean, 40.7°; range, 33.6° to 49.2°), TBB had significantly higher DA (mean ± SE, 1.75 ± 0.04) than SCB plate (1.29 ± 0.04), and mildly diseased TBB had higher DA (1.85 ± 0.06) than severely diseased TBB (1.65 ± 0.06).
Conclusions and Clinical Relevance—The highly ordered appearance of trabeculae within the condyles supports the concept that joint loading is primarily transmitted through the condyles and not the sagittal ridge. The sharp changes in the trajectories of the SCB trabeculae at the condylar grooves may be indicative of hypothetical tensile forces at this location contributing to the pathogenesis of condylar fractures. (Am J Vet Res 2010;71:1148—1153)
Objective—To determine the cardiovascular effects of 60 minutes of abdominal insufflation with CO2 to an intra-abdominal pressure of 15 mm Hg in standing horses receiving a constant rate infusion of detomidine.
Procedure—Horses were randomly allocated into treatment or control groups. A washout period of a minimum of 7 days separated the 2 experimental periods of the crossover study. Catheters were placed into the right atrium, pulmonary artery, jugular vein, and right transverse facial artery after lidocaine infiltration. All horses were sedated with detomidine (8.54 µg/kg/h, IV). Horses in the treatment group received abdominal insufflation with CO2 via a laparoscopic cannula to a final and constant intraabdominal pressure of 15 mm Hg for 60 minutes. Systemic arterial pressure, right atrial pressure, heart rate, cardiac output, core body temperature, and the pH and gas tensions of arterial and mixed venous blood were obtained. Cardiac index and systemic vascular resistance were calculated. Data were collected in 3 stages: preinsufflation (–10 and –5 minutes), insufflation (0, 15, 30, 45, and 60 minutes), and postinsufflation (70 and 80 minutes). The quality of sedation and level of analgesia were determined.
Results—The PaO2 of horses in the treatment group was significantly higher after 60 minutes of pneumoperitoneum than in the control group. Core body temperature decreased significantly from baseline in both groups.
Conclusions and Clinical Relevance—A 60-minute period of abdominal insufflation to an intra-abdominal pressure of 15 mm Hg did not induce significant cardiovascular abnormalities in healthy horses. ( Am J Vet Res 2004;65:357–362)
Objective—To characterize the microstructure of subchondral bone (SCB) plate and trabecular bone (TBB) of the distopalmar aspect of the condyles of third metacarpal bones (MC3s) from Thoroughbred racehorses at 2 different stages of SCB disease via micro–computed tomography (CT).
Sample Population—12 pairs of MC3s from Thoroughbred racehorses euthanized for various reasons.
Procedures—MC3s were collected from horses with mild (n = 6) or severe (6) SCB disease, as determined via micro-CT. Cubic (6 × 6 × 6-cm) specimens of SCB plate and TBB were cut from the palmar aspect of condyles and sagittal ridges and examined with 3-dimensional micro-CT. For each specimen, apparent bone mineral density (aBMD), true BMD (tBMD), bone volume fraction (BVF), trabecular thickness (TBT), trabecular separation (TBS), and connectivity (CN) were calculated.
Results—Condyles had higher aBMD, tBMD, BVF, and TBT and lower TBS than did the sagittal ridge. In bone specimens with mild SCB changes, SCB plate had higher aBMD, TBT, and CN and lower TBS than did TBB. In bone specimens with severe SCB disease, TBB had higher aBMD and TMD and lower TBS than it did in bone specimens with mild disease, and values were similar to those for SCB plate in bone specimens with severe disease.
Conclusions and Clinical Relevance—The microstructure of SCB of the distopalmar aspect of metacarpal condyles of horses varied according to the severity of changes identified via micro-CT. With mild SCB disease, sclerosis existed in the SCB plate of the condyles; with severe disease, sclerosis also invaded condylar TBB.
Objective—To characterize the mechanical properties of subchondral bone (SCB) of the distopalmar aspect of the condyles of the third metacarpal bone (MC3) and their correlations with structural aspects of MC3s in Thoroughbred racehorses.
Sample Population—12 pairs of MC3s from Thoroughbred racehorses euthanized for various reasons.
Procedures—MC3s were collected from horses with mild (n = 6) and with severe (6) SCB changes, as determined by micro–computed tomography (CT). Specimens of SCB plate and trabecular bone were cut from the distopalmar aspect of condyles and sagittal ridge and examined with 3-dimensional micro-CT. Specimens were tested in compression, and elastic modulus, yield stress, yield strain, and toughness were calculated. Apparent and true bone mineral density, bone volume fraction, trabecular thickness, trabecular separation, and connectivity were also calculated. Differences in mechanical properties among various classifications of bone were evaluated. Correlations between structural and mechanical variables were also assessed.
Results—No differences were detected between left and right forelimbs. Specimens from condyles had higher values for elastic modulus, yield stress, and toughness than did specimens of sagittal ridge. In SCB with severe changes attributable to SCB disease, SCB plate was weaker and trabecular bone was stronger than in SCB with mild changes. Microstructural and mechanical properties were significantly correlated.
Conclusions and Clinical Relevance—A marked gradient in mechanical properties of SCB from horses, which could be involved in the pathogenesis of condylar fractures, was detected. Mechanical properties of SCB from the distal aspect of MC3s can be predicted to some extent via micro-CT.
Objective—To determine characteristics, incidence rate, and possible associations with selected demographic characteristics of catastrophic musculoskeletal injuries (CMIs) in Thoroughbred racehorses.
Animals—76 Thoroughbreds with CMIs.
Procedures—Incidence rates of CMIs during racing or training were calculated with number of CMIs as the numerator and overall numbers of races or training events during 2004 and 2005 as the denominators. Exact 95% confidence intervals were calculated. Associations between incidence and dichotomous exposure factors, nominal factors, and ordinal factors were determined. Only univariable associations were examined.
Results—76 horses were euthanized because of CMI and represented 2.36 and 1.69 deaths/1,000 racing starts in 2004 and 2005, respectively. Of these, 57 were euthanized within 60 days before or after a race, which yielded a point incidence of 1.05/1,000 racing starts and 0.39/1,000 training starts.
Conclusions and Clinical Relevance—Incidence rate of CMIs at 2 Ontario racetracks was similar to that at other North American racetracks. A cumulative death rate of 1 to 2 deaths/wkshould be considered typical when designing prevention strategies and offers a baseline value for measuring improvement.
Objective—To use quantitative ultrasonography to evaluate the association between the speed of sound (SOS) at 9 sites in the third metacarpal bone (MCIII) of racing Thoroughbreds with workload accumulation and the effect that MCIII failure has on this association.
Animals—Sixty-two 2- and 3-year-old Thoroughbreds in racing condition.
Procedures—Cumulative work index (CWI) was used to calculate total workload (CWItotal) and also 3 independent CWIs for the various gaits (ie, trot [CWItrot], gallop [CWIgallop], and race [CWIrace]) used during training and racing. Speed of sound was monitored in horses during the 2007 racing season and compared with the CWIs via regression analysis. Sex, age, limb, and MCIII failure were included as covariates in the model.
Results—SOS was significantly associated with CWItotal at 8 sites and with independent CWIs of the various gaits at all 9 sites. Progression of SOS in MCIIIs with workload differed significantly in horses with clinical signs of metacarpal bone failure, compared with results for horses with clinically normal MCIIIs, in 1 site by use of CWItotal and in 5 sites by use of the independent CWIs for the various gaits.
Conclusions and Clinical Relevance—These results indicated that SOS in the MCIII of racing Thoroughbreds followed a constant pattern of progression as workload accumulated. With the development of more precise quantitative ultrasonography devices, SOS corrected for amount of activity may be used to identify horses at risk of bone failure.