Impaired abomasal motility is common in cattle with abomasal disorders. The macrolide erythromycin has been demonstrated to be an effective prokinetic agent in healthy calves and in adult cattle with abomasal volvulus or left displaced abomasum. We hypothesized that 2 structurally related macrolides, spiramycin and tulathromycin, would also be effective prokinetic agents in cattle. Six milk-fed, male, Holstein-Friesian calves were administered each of the following 4 treatments: spiramycin, 75 000 IU/kg BW, IM, this dose approximates 25 mg/kg BW, IM; tulathromycin, 2.5 mg/kg BW, SC; 2 mL of 0.9% NaCl (negative control); and erythromycin, 8.8 mg/kg BW, IM (positive control). Calves were fed 2 L of cow's milk containing acetaminophen (50 mg/kg body weight) 30 min after each treatment was administered and jugular venous blood samples were obtained periodically after the start of sucking. Abomasal emptying rate was assessed by the time to maximal plasma acetaminophen concentration. Spiramycin, tulathromycin, and the positive control erythromycin increased abomasal emptying rate compared to the negative control. We conclude that the labeled antimicrobial dose of spiramycin and tulathromycin increases the abomasal emptying rate in healthy milk-fed calves. Additional studies investigating whether spiramycin and tulathromycin exert a prokinetic effect in adult cattle with abomasal hypomotility appear indicated.

Objective-To determine pharmacodynamic cutoffs with pharmacokinetic-pharmacodynamic principles and Monte Carlo simulation (MCS) for use of amoxicillin in pigs to set interpretive criteria for antimicrobial susceptibility testing. Sample-191 plasma disposition curves of amoxicillin obtained from 21 IV, 104 IM, and 66 PO administrations corresponding to 2,098 plasma concentrations. Procedures-A population model of amoxicillin disposition in pigs was developed for PO and IM administration. The MCS method was then used to determine, for various dosage regimens, the proportion of pigs achieving plasma amoxicillin concentrations greater than a selection of possible minimal inhibitory concentrations (MICs) ranging from 0.0625 to 4 mg/L for at least 40% of a 24-hour period. Results-A target attainment rate (TAR) of 90% was never achieved with the breakpoint recommended by the Clinical and Laboratory Standards Institute (0.5 mg/L) when the usual recommended dosage (20 mg/kg/d) was used. Only by dividing the orally administered daily dose into 12-hour administration intervals was a TAR > 90% achieved when the total dose was at least 40 mg/kg for a pathogen having an MIC ≤ 0.0625 mg/L. For the IM route, the TAR of 90% could only be achieved for MICs of 0.0625 and 0.125 mg/L with the use of 15 and 30 mg/kg doses, respectively. Conclusions and Clinical Relevance-Population kinetics and MCS are required to determine robust species-specific interpretive criteria (susceptible, intermediate, and resistant classifications) for antimicrobial susceptibility testing breakpoints (taking into account interanimal variability).

Objective-To determine associations of blood analysis variables and orbit and nasal planum surface temperatures with the onset and severity of Mycoplasma bovis pneumonia in calves. Animals-28 healthy calves. Procedures-Calves were challenged with M bovis (n = 24) on day 0 or not challenged (4). Blood samples were obtained for cardiac troponin I, CBC, and serum biochemical analyses on various days. Orbit and nasal planum surface temperatures were determined with infrared thermography on various days. Calves were euthanized, gross necropsies were performed, heart and lung samples were collected for histologic evaluation, and microbial cultures of lung samples were performed on day 14. Pneumonia severity was categorized as mild (< 10% lung consolidation) or moderate (≥ 10% lung consolidation). Associations between measured variables and severity of pneumonia or sample collection day were determined. Results-Plasma cardiac troponin I concentration for the 28 calves was significantly higher on day 14 than it was on day 0 or 7 (least squares mean, 0.02, 0, and 0 ng/mL, respectively). No other variables changed significantly during the study. No substantial gross or histologic abnormalities were identified in cardiac muscle samples. Day 14 plasma fibrinogen concentration was significantly different between calves with mild pneumonia and those with moderate pneumonia (mean, 0.44 and 0.74 g/dL, respectively). Calves with moderate pneumonia had significantly lower least squares mean surface temperature of the dorsal aspect of the nasal planum (18.7°C) versus calves with mild pneumonia (22.9°C). Conclusions and Clinical Relevance-Results indicated the evaluated variables had low value for assessment of bovine respiratory disease complex in calves.

Objective-To determine the accuracy of neurologic data, survey radiographic results, or both for localization of the site of thoracolumbar intervertebral disk herniation in dogs. Sample-338 dogs with surgically confirmed intervertebral disk herniation from disk spaces T10-11 to L6-7. Procedures-Medical records and archived survey radiographs were reviewed for each case. Data were analyzed with multivariable logistic regression models. Three models were fit to develop subsets of the data consisting of survey radiographic data, neurologic examination data, and a combination of survey radiographic and neurologic examination data. The resulting models were validated by evaluating predictive performance against a validation subset of the data. Results-Models incorporating survey radiographic data and a combination of survey radiographic and neurologic data had similar predictive ability and performed better than the model based solely on neurologic data but resulted in substantial errors in predictions. Conclusions and Clinical Relevance-A combination of neurologic examination data as recorded in the medical records and radiographic data did not enhance predictive performance of multivariable logistic regression models over models limited to radiographic data. Neurologic and radiographic findings should not be used to completely exclude areas in an abnormal spinal cord region from further evaluation with advanced imaging.

Objective-To validate use of stress MRI for evaluation of stifle joints of dogs with an intact or deficient cranial cruciate ligament (CrCL). Sample-10 cadaveric stifle joints from 10 dogs. Procedures-A custom-made limb-holding device and a pulley system linked to a paw plate were used to apply axial compression across the stifle joint and induce cranial tibial translation with the joint in various degrees of flexion. By use of sagittal proton density-weighted MRI, CrCL-intact and deficient stifle joints were evaluated under conditions of loading stress simulating the tibial compression test or the cranial drawer test. Medial and lateral femorotibial subluxation following CrCL transection measured under a simulated tibial compression test and a cranial drawer test were compared. Results-By use of tibial compression test MRI, the mean +/- SD cranial tibial translations in the medial and lateral compartments were 9.6 +/- 3.7 mm and 10 +/- 4.1 mm, respectively. By use of cranial drawer test MRI, the mean +/- SD cranial tibial translations in the medial and lateral compartments were 8.3 +/- 3.3 mm and 9.5 +/- 3.5 mm, respectively. No significant difference in femorotibial subluxation was found between stress MRI techniques. Femorotibial subluxation elicited by use of the cranial drawer test was greater in the lateral than in the medial compartment. Conclusions and Clinical Relevance-Both stress techniques induced stifle joint subluxation following CrCL transection that was measurable by use of MRI, suggesting that both methods may be further evaluated for clinical use.

Objective—To determine whether stromal cell-derived factor-1 (SDF-1) concentrations in serum, plasma, and synovial fluid differed among untrained, race-trained, and osteochondral-injured Thoroughbred racehorses. Animals—22 racehorses without osteochondral injury and 37 racehorses with osteochondral injury. Procedures—Horses without osteochondral injury were examined before and after 5 to 6 months of race training. Horses with osteochondral injury were undergoing arthroscopic surgery for removal of osteochondral fragments from carpal or metacarpophalangeal or metatarsophalangeal joints (fetlock joints). Serum, plasma, and fetlock or carpal synovial fluid samples were obtained and analyzed for SDF-1 concentration by use of an ELISA. Results—In horses with fetlock or carpal joint injury, mean synovial fluid SDF-1 concentrations were significantly higher, serum SDF-1 concentrations were significantly lower, and synovial fluid-to-serum SDF-1 ratios were significantly higher than in untrained and trained horses. Synovial fluid SDF-1 concentrations were not significantly different between trained and untrained horses. Plasma SDF-1 concentrations were not different among the 3 groups. Results obtained with serum, compared with synovial fluid and plasma, had better sensitivity for differentiating between osteochondral-injured horses and uninjured horses. In horses with fetlock joint osteochondral injury, serum SDF-1 concentrations were correlated with radiographic and arthroscopic inflammation scores, but not arthroscopic cartilage scores. Conclusions and Clinical Relevance—Results suggested that serum SDF-1 concentrations were more sensitive than plasma and synovial fluid concentrations for detection of osteochondral injury in the fetlock or carpal joint of racehorses. Analysis of serum and synovial SDF-1 concentrations in horses with experimentally induced joint injury may help define the onset and progression of post-traumatic osteoarthritis and aid in the evaluation of anti-inflammatory treatments.

Objective—To determine dose dependency of tranexamic acid–induced emesis and the time course of the antifibrinolytic potency of tranexamic acid in dogs. Animals—10 Beagles. Procedures—In a dose-escalating experiment, ascending doses of tranexamic acid (10, 20, and 30 mg/kg, IV) were administered at 5-minute intervals until vomiting was observed. In a separate single-dose experiment, ascending doses of tranexamic acid (20, 30, 40, and 50 mg/kg, IV) were administered at 1-week intervals until vomiting was observed. Time to onset of vomiting and number of vomiting episodes were measured in both experiments. In a coagulation experiment, a single 50 mg/kg bolus of tranexamic acid was administered, and blood was obtained 1 hour before and 20 minutes, 3 hours, and 24 hours after administration. Antifibrinolytic potency of tranexamic acid was evaluated by use of a modified rotational thromboelastography method. Results—Tranexamic acid induced vomiting in a dose-dependent manner. Vomiting frequency was < 2 episodes, and vomiting concluded < 250 seconds after administration. Antifibrinolytic potency of tranexamic acid was significantly higher at 20 minutes following administration, but not different by 24 hours, when compared with the potency measured before administration. No adverse effects were observed in any experiment. Conclusions and Clinical Relevance—IV administration of tranexamic acid induced emesis in a dose-dependent manner. The antifibrinolytic potency of tranexamic acid decreased in a time-dependent manner and was resolved < 24 hours after administration. Further studies are warranted to investigate the emetic and other adverse effects of tranexamic acid in dogs of various breeds and ages.

Objective—To describe findings of 3.0-T multivoxel proton magnetic resonance spectroscopy (1H-MRS) in dogs with inflammatory and neoplastic intracranial disease and to determine the applicability of 1H-MRS for differentiating between inflammatory and neoplastic lesions and between meningiomas and gliomas. Animals—33 dogs with intracranial disease (19 neoplastic [10 meningioma, 7 glioma, and 2 other] and 14 inflammatory). Procedures—3.0-T multivoxel 1H-MRS was performed on neoplastic or inflammatory intracranial lesions identified with conventional MRI. N-acetylaspartate (NAA), choline, and creatine concentrations were obtained retrospectively, and metabolite ratios were calculated. Values were compared for metabolites separately, between lesion categories (neoplastic or inflammatory), and between neoplastic lesion types (meningioma or glioma) by means of discriminant analysis and 1-way ANOVA. Results—The NAA-to-choline ratio was 82.7% (62/75) accurate for differentiating neoplastic from inflammatory intracranial lesions. Adding the NAA-to-creatine ratio or choline-to-creatine ratio did not affect the accuracy of differentiation. Neoplastic lesions had lower NAA concentrations and higher choline concentrations than inflammatory lesions, resulting in a lower NAA-to-choline ratio, lower NAA-to-creatine ratio, and higher choline-to-creatine ratio for neoplasia relative to inflammation. No significant metabolite differences between meningiomas and gliomas were detected. Conclusions and Clinical Relevance—1H-MRS was effective for differentiating inflammatory lesions from neoplastic lesions. Metabolite alterations for 1H-MRS in neoplasia and inflammation in dogs were similar to changes described for humans. Use of 1H-MRS provided no additional information for differentiating between meningiomas and gliomas. Proton MRS may be a beneficial adjunct to conventional MRI in patients with high clinical suspicion of inflammatory or neoplastic intracranial lesions.

Objective—To evaluate the use of a micro-lightguide tissue spectrophotometer for measurement of tissue oxygenation and blood flow in the small and large intestines of horses under anesthesia. Animals—13 adult horses without gastrointestinal disease. Procedures—Horses were anesthetized and placed in dorsal recumbency. Ventral midline laparotomy was performed. Intestinal segments were exteriorized to obtain measurements. Spectrophotometric measurements of tissue oxygenation and regional blood flow of the jejunum and pelvic flexure were obtained under various conditions that were considered to have a potential effect on measurement accuracy. In addition, arterial oxygen saturation at the measuring sites was determined by use of pulse oximetry. Results—12,791 single measurements of oxygen saturation, relative amount of hemoglobin, and blood flow were obtained. Errors occurred in 381 of 12,791 (2.98%) measurements. Most measurement errors occurred when surgical lights were directed at the measuring site; covering the probe with the surgeon's hand did not eliminate this error source. No measurement errors were observed when the probe was positioned on the intestinal wall with room light, at the mesenteric side, or between the mesenteric and antimesenteric side. Values for blood flow had higher variability, and this was most likely caused by motion artifacts of the intestines. Conclusions and Clinical Relevance—The micro-lightguide spectrophotometry system was easy to use on the small and large intestines of horses and provided rapid evaluation of the microcirculation. Results indicated that measurements should be performed with room light only and intestinal motion should be minimized.

Objective—To evaluate the effect of multiple hydrogen peroxide gas plasma (HPGP) sterilizations on the rate of closure of ameroid constrictors. Sample—Thirty-six 5.0-mm ameroid constrictors. Procedures—Ameroid constrictors were randomly allocated to 6 groups. Each group underwent 1, 2, 3, 4, 5, or 6 HPGP sterilizations. Ameroid constrictors were then incubated for 35 days in canine plasma and digitally imaged at predetermined times during incubation. One individual, who was unaware of the group to which each ameroid constrictor was assigned, measured the lumen area of the constrictor on each digital image. Mean lumen area was compared among groups. Results—No ameroid constrictors were completely closed after 35 days of incubation in canine plasma. Mean lumen area after incubation did not differ among constrictors that underwent 1, 2, and 3 sterilizations. Constrictors that underwent 4 sterilizations were closed significantly more than were those that underwent 1, 2, or 3 sterilizations. Mean lumen area after incubation did not differ significantly between constrictors that underwent 5 and 6 sterilizations, although the final lumen areas for those constrictors were significantly smaller than those for constrictors that underwent 1, 2, 3, and 4 sterilizations. Conclusions and Clinical Relevance—Ameroid constrictors that underwent 5 and 6 HPGP sterilizations had a 9% to 12% decrease in lumen area, compared with that of constrictors that underwent ≤ 4 plasma sterilizations, and the use of such constrictors could increase the risk of portal hypertension and secondary acquired shunting or decrease the risk of persistent shunting.