John P. Caron

Retrospective multicentre study of methicillin-resistant Staphylococcus aureus infections in 115 horses.

REASONS FOR PERFORMING STUDY Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging veterinary and zoonotic pathogen, associated with increasing reports of disease in horses. OBJECTIVES To provide an overview of the characteristics of clinical MRSA infections in horses. METHODS A retrospective case study was performed on 115 horses admitted to 6 participating veterinary teaching hospitals in Canada and the United States between 2000 and 2006, and diagnosed with clinical MRSA infection. Descriptive statistics, univariate and multivariable analyses for community- (CA) vs. hospital-associated (HA) MRSA infections, and survival vs. nonsurvival at discharge were performed. RESULTS The age range of MRSA-infected horses was zero (born in hospital) to 31 years. HA (58/114, 50.9%) and CA infections (56/114, 49.1%) were equally common. Infection of surgical incisions was most frequently reported (44/115, 38.0%). Overall 93/111 (83.8%) cases survived to discharge. Previous hospitalisation and treatment with gentamicin were associated significantly with CA-MRSA, whereas infected incision sites were associated significantly with HA-MRSA. Factors significantly associated with nonsurvival included i.v. catheterisation, CA-MRSA infection and dissemination of infection to other body sites. CONCLUSIONS Equine MRSA infections have a broad range of clinical presentations, appear to be primarily opportunistic and the overall prognosis for survival to discharge is good. POTENTIAL RELEVANCE These results should help direct future research with regard to investigation of risk factors for equine MRSA infection in community and hospital populations.

Intracorporeal Suture Closure of the Internal Inguinal and Vaginal Rings in Foals and Horses

OBJECTIVE To report a technique for repair or prevention of inguinal hernia in horses using intracorporeal suture closure of the internal inguinal and vaginal rings. STUDY DESIGN Case series. ANIMALS Foals (n=6) and geldings (n=2). METHODS After selection of a peri-umbilical telescope portal, instrument portals were made unilaterally or bilaterally, as needed. Herniated viscera was reduced, castration (foals) or spermatic cord remnant transection at the internal inguinal ring (adults) performed, and then simple interrupted intracorporeal sutures of synthetic absorbable suture material were used to close the internal inguinal and vaginal rings. RESULTS There was no recurrence of inguinal hernia. Postoperative morbidity was minimal and cosmetic outcome was comparable to that achieved with conventional, open techniques. CONCLUSION Laparoscopic, primary closure of the internal inguinal ring by use of intracorporeal sutures provides a secure barrier to herniation and costs considerably less than using endoscopic staples. CLINICAL RELEVANCE Laparoscopic suture closure of the internal inguinal and vaginal rings provides safe and effective repair of inguinal hernia in horses.

Laparoscopic mesh incisional hernioplasty in five horses.

OBJECTIVE To report a technique for incisional hernioplasty in horses using laparoscopic placement of a prosthetic mesh. STUDY DESIGN Case series. ANIMALS Horses (n=5) with ventral median abdominal incisional hernia. METHODS A telescope and 2 instrument portals were established bilaterally, lateral to and distant from the hernia margins. After exposure of the internal rectus sheath by removal of retroperitoneal fat with endoscopic scissors and monopolar cautery, a prosthetic mesh was introduced into the abdomen and secured intraperitoneally using transfascial sutures with or without supplemental endoscopic hernia fixation devices. RESULTS Successful placement of the prostheses was achieved without major intra- or postoperative complications. Repairs were intact in all horses (follow-up range: 6-23 months) without evidence of adhesion formation. Cosmetic results compared favorably with those typically achieved using conventional, open hernioplasty techniques. CONCLUSION Incisional hernia repair in horses can be successfully achieved with a laparoscopic intraperitoneal mesh onlay technique. CLINICAL RELEVANCE Laparoscopic mesh hernioplasty has promise as a safe and effective method for repair of incisional hernias in horses.

Substance P innervation of equine synovial membranes: joint differences and neural and nonneural receptor localizations

Substance P (SP) immunocytochemistry and receptor autoradiography were used to define the innervation of the equine synovial membrane of joints equivalent to the wrist and knuckle of man. SP-immunoreactive fibers were mainly concentrated around blood vessels in the subsynovial layer, although not exclusively, while in the more distal joint, SP fibers were more frequently seen in the synovial surface layer. Iodinated SP receptor autoradiography studies revealed silver grain concentrations in the advential layer of blood vessels associated with the vasa vasorum, on the vascular endothelium and in the synovial surface. These findings suggest that SP has various sites of action within the synovial membrane, each of which may contribute both a sensory function and a different component of the inflammatory process to the joint.

Adipose tissue remodeling in late-lactation dairy cows during feed-restriction-induced negative energy balance

Excessive rates of demand lipolysis in the adipose tissue (AT) during periods of negative energy balance (NEB) are associated with increased susceptibility to disease and limited lactation performance. Lipolysis induces a remodeling process within AT that is characterized by an inflammatory response, cellular proliferation, and changes in the extracellular matrix (ECMT). The adipose tissue macrophage (ATM) is a key component of the inflammatory response. Infiltration of ATM-forming cellular aggregates was demonstrated in transition cows, suggesting that ATM trafficking and phenotype changes may be associated with disease. However, it is currently unknown if ATM infiltration occurs in dairy cows only during NEB states related to the transition period or also during NEB-induced lipolysis at other stages of lactation. The objective of this study was to evaluate changes in ATM trafficking and inflammatory phenotypes, and the expression of genetic markers of AT remodeling in healthy late-lactation cows during feed restriction-induced NEB. After a 14-d (d -14 to d -1) preliminary period, Holstein cows were randomly assigned to 1 of 2 feeding protocols, ad libitum (AL) or feed restriction (FR), for 4 d (d 1-4). Caloric intake was reduced in FR to achieve a targeted energy balance of -15 Mcal/d of net energy for lactation. Omental and subcutaneous AT samples were collected laparoscopically to harvest stromal vascular fraction (SVF) cells on d -3 and 4. The FR induced a NEB of -14.1±0.62 Mcal/d of net energy for lactation, whereas AL cows remained in positive energy balance (3.2±0.66 Mcal/d of NEL). The FR triggered a lipolytic response reflected in increased plasma nonesterified fatty acids (0.65±0.05 mEq/L on d 4), enhanced phosphorylation of hormone sensitive lipase, and reduced adipocyte diameter. Flow cytometry and immunohistochemistry analysis revealed that on d 4, FR cows had increased numbers of CD172a+, an ATM (M1 and M2) surface marker, cells in SVF that were localized in aggregates. However, FR did not alter the number of SVF cells expressing M1 markers (CD14 and CD11c) or M2 markers (CD11b and CD163). This finding contrasts with the predominately M1 phenotype observed previously in ATM from clinically diseased cows. No changes were observed in the expression of ECMT-related or cell proliferation markers. In summary, an acute 4-d lipolytic stimulus in late-lactation dairy cows led to ATM infiltration with minimal changes in inflammatory phenotype and no changes in ECMT. These results underscore that physiological changes related to parturition, the onset of lactation, extended periods of lipolysis, or a combination of these can induce intense AT remodeling with enhanced ATM inflammatory phenotype expression that may impair the metabolic function of AT in transition dairy cattle.

Minimum Inhibitory Concentration and Postantibiotic Effect of Amikacin for Equine Isolates of Methicillin‐Resistant Staphylococcus aureus In Vitro

OBJECTIVE To report the minimum inhibitory concentration (MIC) of amikacin sulfate for equine clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and characterize the initial kill and duration of the postantibiotic effect (PAE) for selected strains. STUDY DESIGN Experimental study. METHODS Isolates of MRSA (n=35) had their amikacin MIC determined using the E-test agar diffusion method. Two isolates with MICs>256 microg/mL limit were further characterized using broth macrodilution. Six distinct isolates with amikacin MICs of 32, 48, 128 (2 isolates) and 500 (2 isolates) microg/mL had PAE determinations made over a range of amikacin concentrations from 31.25-1000 microg/mL using standard culture-based techniques. RESULTS Median MIC of the 35 isolates was 32 microg/mL (range 2 to >256 microg/mL). Mean PAE of selected MRSA strains had an overall mean (all amikacin doses) of 3.43 hours (range 0.10-9.57 hours). PAE for MRSA exposed to amikacin at 1000 microg/mL was 6.18 hours (range 3.30-9.57 hours), significantly longer than that for all other concentrations (P<.0001). There was no statistically significant effect of isolate MIC on PAE. CONCLUSIONS Isolates had a wide range of MIC; however, growth of all 6 selected strains were inhibited within the range of concentrations tested, including 2 strains with MICs of 500 microg/mL. PAE duration was not influenced by the MIC of amikacin but was significantly longer with treatment at 1000 microg/mL than at lower concentrations. CLINICAL RELEVANCE Clinical isolates of MRSA are susceptible to amikacin at concentrations achieved by regional perfusion: however, the modest duration of PAE observed suggest that further laboratory and in vivo evaluation be conducted before recommending the technique for clinical use.

Influence of Corticosteroids on Interleukin-1β-Stimulated Equine Chondrocyte Gene Expression

OBJECTIVE To compare the effects of triamcinolone acetonide (TA) and methylprednisolone acetate (MPA) on expression of selected chondrocyte genes in recombinant equine interleukin-1β (reIL-1β) stimulated articular cartilage explants. DESIGN In vitro experiment. ANIMALS Horses (n = 6). PROCEDURES Articular cartilage explants from 2- to 3- year-old horses were exposed to reIL-1β in the presence and absence of TA and MPA at 10(-7) and 10(-6) M. Resting levels of mRNA of anabolic and catabolic genes of chondrocyte origin were quantified using qPCR after 6- and 12-hour incubations. Genes of interest included aggrecan interglobular domain, aggrecan, and collagen II, matrix metalloproteinases 3 and 13 (MMP3, MMP 13), aggrecanase 1, tissue inhibitor of matrix metalloproteinases 1 and 2 (TIMP 1, TIMP 2), BCL 2, vascular endothelial growth factor, and cyclooxygenase 2 (COX 2). RESULTS IL-1β significantly influenced the expression of most transcripts. MPA and TA inhibited the induction of MMP 13 at 6 and 12 hours; an effect that was significant at 6 hours with MPA at 10(-7) M and TA at 10(-6) M. Similarly, COX 2 was induced by reIL-1β and MPA and TA significantly inhibited its upregulation. TIMP 2 expression was reduced by reIL-1β, an effect that was significantly abrogated by MPA and TA. There were no significant differences observed between glucocorticoids for any gene studied. CONCLUSIONS No differential effects of MPA or TA on chondrocytic gene expression were identified suggesting that any divergent influences of these glucocorticoids on chondrocyte metabolism are posttranslational.

Navicular Bursoscopy in the Horse: A Comparative Study

OBJECTIVES To compare the proportion of the proximal recess of the navicular bursa that could be examined through a single endoscopic portal and the severity of iatrogenic lesions between conventional and modified approaches. DESIGN Descriptive study. SAMPLE POPULATION Equine cadaver forelimbs (n=16). METHODS Arthroscopic access to the navicular bursa in 1 limb of each pair was by a conventional approach and in the other limb, by a modified approach using sharp dissection through the distal digital flexor sheath, immediately palmar to the T ligament. The time required to access the bursa and the estimated proportion of the navicular bone that could be seen with each approach were recorded. Iatrogenic damage to the navicular bone and the deep digital flexor tendon (DDFT) were quantified. RESULTS The mean access time to the navicular bursa using the conventional approach was 1.21+/-0.41 minutes compared with 2.09+/-0.86 minutes using the modified technique. The estimated proportions of the bursa visible through a single endoscopic portal using the conventional and modified approaches were 60% and 80%, respectively. Scores for navicular bone (P=.003) and DDFT (P=.012) damage using the conventional approach were significantly higher than those using the modified approach. CONCLUSIONS A modified, transthecal approach to the navicular bursa under direct observation resulted in significantly less iatrogenic damage than the conventional approach. CLINICAL RELEVANCE With experience, the modified approach is straightforward, reasonably rapid, and allows near-complete examination of the navicular bursa through a single portal, with minimal iatrogenic damage to the intrabursal structures.

Incisional hernia repair in horses: A cadaveric study of endoscopic component separation

Objective To report a technique for endoscopic component separation in horses and quantify the amount of body wall advancement obtained. Study Design Descriptive study. Animals Fresh cadaveric horses (n = 14). Methods After a preliminary anatomic study, 7 horses had unilateral endoscopic component separation involving transection of the external abdominal oblique fascia lateral to the rectus abdominis muscle. A laparoscope, placed using a balloon dissector, was used to create an intermuscular working space between the external abdominal oblique fascia and internal abdominal oblique muscle. A single instrument portal was created 10–12 cm medial to the laparoscope portal. Laparoscopic scissors were used to transect the external abdominal oblique fascia, lateral to its insertion to the external rectus sheath, from ∼20 cm cranial to the costochondral junction to the level of the superficial inguinal ring. Subsequently, a 30 cm ventral median celiotomy was created and the myofascial advancement was quantified at points 10 and 20 cm cranial to the umbilicus. Results Endoscopic component separation was successfully completed in all horses. Component separation provided a net mean (±SD) abdominal wall advancement of 3.5 ± 1.3 cm and 3.4 ± 0.5 cm, 10 cm, and 20 cm cranial to the umbilicus, respectively. Conclusion Endoscopic component separation in horses is technically feasible but, as conducted, results in modest abdominal wall advancement.OBJECTIVE To report a technique for endoscopic component separation in horses and quantify the amount of body wall advancement obtained. STUDY DESIGN Descriptive study. ANIMALS Fresh cadaveric horses (n = 14). METHODS After a preliminary anatomic study, 7 horses had unilateral endoscopic component separation involving transection of the external abdominal oblique fascia lateral to the rectus abdominis muscle. A laparoscope, placed using a balloon dissector, was used to create an intermuscular working space between the external abdominal oblique fascia and internal abdominal oblique muscle. A single instrument portal was created 10-12 cm medial to the laparoscope portal. Laparoscopic scissors were used to transect the external abdominal oblique fascia, lateral to its insertion to the external rectus sheath, from ≈ 20 cm cranial to the costochondral junction to the level of the superficial inguinal ring. Subsequently, a 30 cm ventral median celiotomy was created and the myofascial advancement was quantified at points 10 and 20 cm cranial to the umbilicus. RESULTS Endoscopic component separation was successfully completed in all horses. Component separation provided a net mean (± SD) abdominal wall advancement of 3.5 ± 1.3 cm and 3.4 ± 0.5 cm, 10 cm, and 20 cm cranial to the umbilicus, respectively. CONCLUSION Endoscopic component separation in horses is technically feasible but, as conducted, results in modest abdominal wall advancement.

Nephrectomy via ventral median celiotomy in equids.

OBJECTIVE To report technique for, and outcome after, nephrectomy through a ventral median celiotomy in equids. STUDY DESIGN Case series. ANIMALS Equids with unilateral renal disease (n = 6), aged 2 months to 18 years, weighing 90-434 kg. METHODS A ventral median celiotomy was used to access the left or right kidney. To facilitate surgical exposure, the small intestine was reflected towards the diaphragm using laparotomy sponges and the ascending colon was exteriorized and in some cases evacuated. The peritoneum over the affected kidney was incised and blunt dissection used to free the kidney from the retroperitoneal fat, then the renal artery, vein, and ureter were isolated and ligated. Abdominal lavage with sterile saline solution was performed before abdominal closure. RESULTS Four horses, 1 donkey, and 1 mule had unilateral nephrectomy to treat verminous nephritis (1), idiopathic hematuria (1), and ectopic ureter (4). A ventral median approach provided adequate access to the kidney in all 6 cases. Two horses had postoperative complications (peritonitis, chylous abdominal effusion) that resolved with medical therapy. No complications attributable to nephrectomy were reported by the owners upon follow-up 1-8 years after surgery. CONCLUSIONS A ventral median approach for nephrectomy can be used for unilateral nephrectomy in equids weighing up to 434 kg.