REASONS FOR PERFORMING STUDY: Current labeling for the use of ceftiofur crystalline free acid (CCFA) in horses states that 2 intramuscular (i.m.) doses must be administered 4 days apart to provide 10 days of therapeutic coverage. A 10-day treatment regimen is not sufficient for the long term treatment of horses with severe lung consolidation or pleuropneumonia. There are currently no data to guide an appropriate dosing interval when a longer treatment regimen is warranted.

OBJECTIVES:

To determine steady-state plasma and pulmonary epithelial lining fluid (PELF) concentrations of desfuroylceftiofur acetamide (DCA) after weekly i.m. administration of CCFA to adult horses.

Study design:

Experimental study.

METHODS:

Seven adult horses received i.m. CCFA at a dose of 6.6 mg/kg on Day 0, Day 4, and every 7 days thereafter for 3 additional doses. Concentrations of DCA in plasma and PELF were measured at various time intervals.

RESULTS:

After weekly i.m. administration, mean (± s.d.) steady state peak DCA concentration in plasma (2.87 ± 1.50 μg/mL) was significantly higher than that in PELF (0.84 ± 0.53 μg/mL). Mean terminal half-lives in plasma (77.5 ± 17.5 h) and PELF (92.8 ± 59.0 h) were not significantly different. Concentrations of DCA in plasma and PELF remained in the therapeutic range for the entire dosing interval.

CONCLUSIONS:

After the initial 2-dose regimen 4 days apart, weekly i.m. administration of CCFA was well tolerated and resulted in plasma and PELF DCA concentrations above the MIC90 of common lower respiratory tract pathogens of horses. Weekly administration of CCFA would appear appropriate when a treatment regimen longer than 10 days is warranted based on clinical signs and disease severity.

REASON FOR PERFORMING THE STUDY: Infiltration of the equine maxillary nerve with local anaesthetic can be useful for both diagnostic and surgical procedures The deep location and proximity of the nerve to surrounding vascular and orbital structures makes an accurate, complication-free injection a challenge using traditional techniques reliant upon surface anatomical landmarks.

OBJECTIVES:

To develop an ultrasound-guided injection technique of the maxillary nerve in equine cadavers, and evaluate its efficacy and potential for complications in vivo.

STUDY DESIGN:

Descriptive cadavar anatomical and clinical study.

METHODS:

The relevant anatomy of the pterygopalatine fossa was reviewed in 6 cadaver heads from mature horses of a range of ages, breeds and genders. In an additional 13 cadaver heads, ultrasound guided injection of 0.2 ml New Methylene Blue dye was performed on both left and right maxillary nerves (n = 26 attempts) in the pterygopalatine fossa. An independent observer dissected the area and recorded the number of times dye successfully contacted the nerve, along with inadvertent penetration of other structures. The procedure was then performed on 8 clinical cases undergoing a variety of standing surgical procedures of the head.

RESULTS:

Dye was successfully deposited in contact with the nerve during all attempts on cadaver heads, with no penetration of the orbital cone, deep facial vein, and maxillary artery or associated branches. In a single cadaver, a unilateral gas artifact in the masseter muscle prohibited an injection attempt. Analgesia of the maxillary nerve was achieved in <15 min in all clinical cases with complete loss of ipsilateral cutaneous sensation over the rostral face. No gross or ultrasonographic abnormalities were detected following the procedure.

CONCLUSION:

Using ultrasonographic landmarks of the pterygopalatine fossa, local anaesthetic can be deposited around the maxillary nerve without the inadvertent penetration of adjacent vital structures. The technique allows for vascular structures to be visualised and avoided, which is currently not possible using traditional blind approaches.

REASONS FOR PERFORMING THE STUDY: Current diagnosis of recurrent laryngeal neuropathy (RLN) depends upon disease recognition in the clinically affected horse. Biopsy of the intrinsic laryngeal muscles may provide a method to identify the changes in fibre-type composition that occur in RLN before clinical signs become apparent.

OBJECTIVE:

To develop an ultrasound-guided biopsy technique of the left cricoarytenoideus lateralis muscle (CALM), and evaluate its efficacy and safety in vivo.

STUDY DESIGN:

A longitudinal descriptive study

METHODS:

Six standing horses underwent ultrasound guided biopsy of the left CALM. Frozen muscle cores were obtained with a breast biopsy tool. Serial endoscopic, ultrasonographic and physical examinations before and for 8 weeks after the biopsy were assessed for iatrogenic trauma. Histology of representative muscle core cross-sections were analysed for the total number of muscle fibres obtained with each biopsy.

RESULTS:

There were no immediate complications of the procedure, and the left CALM was harvested in all instances. Biopsy samples had an average weight of 0.043 g (range = 0.023-0.077 g) and contained 3418 fibres in cross-section (range = 711 - 7143). Laryngeal endoscopic grade did not change significantly between pre-biopsy and the end of the 8-week follow up. The left CALM had significantly greater echogenicity compared to the right throughout the study (P<0.001), but there was no difference between the pre-biopsy CALM echogenicity and that at completion of the study.

CONCLUSIONS:

Ultrasound guided biopsy of the left CALM is safe and well tolerated, providing a minimally invasive method to obtain muscle from healthy horses. This new technique may be applicable in research and clinical settings.

Mathematical modelling of infectious disease is increasingly regarded as an important tool in the development of disease prevention and control measures. This article brings together key findings from various modelling studies conducted over the past 10 years that are of relevance to those on the front line of the battle against equine influenza.

REASONS FOR PERFORMING STUDY: Although fractures of the proximal phalanx are one of the most common long bone fractures of Thoroughbred horses in training, limited details on variations in morphology and radiologic progression have been published.

OBJECTIVES:

To describe in detail the configuration of parasagittal fractures of the proximal phalanx in a group of Thoroughbred racehorses, to report fracture distribution within this group of horses, and to document radiologic progression of fracture healing in cases treated by internal fixation.

STUDY DESIGN:

Restrospective case series.

METHODS:

Case records and radiographs of Thoroughbred racehorses with parasagittal fractures of the proximal phalanx admitted to Newmarket Equine Hospital between 2007 and 2011 were analysed.

RESULTS:

One hundred and twenty-one fractures were identified in 120 Thoroughbred racehorses. Fractures were frequently more complex than was appreciated immediately following injury; a feature that has not been reported previously. There was seasonality of fractures in 2 and 3-year-old horses, but not in older horses.

CONCLUSIONS

AND POTENTIAL RELEVANCE: Fractures of the proximal phalanx may be more complex than recognised previously, although often their complexity cannot be identified radiographically immediately following injury. The seasonality observed in 2 and 3-year-old horses most likely is a consequence of the timing of the turf racing season in the UK.

REASONS FOR PERFORMING STUDY: Fractures of the proximal phalanx are generally considered to result from monotonic supraphysiologic loads, but radiologic observations from clinical cases suggest there may be stress related aetiology.

OBJECTIVES:

To determine if there are radiologically identifiable prodromal changes in Thoroughbred racehorses with confirmed parasagittal fractures of the proximal phalanx.

STUDY DESIGN:

Retrospective cross-sectional study.

METHODS:

Analysis of case records and radiographs of Thoroughbred racehorses with parasagittal fractures of the proximal phalanx was performed. Thickness of the subchondral bone plate was measured in fractured and contralateral limbs, and additional radiological features consistent with prodromal fracture pathology documented.

RESULTS:

The subchondral bone plate was significantly thicker in affected compared to contralateral limbs. Evidence of additional prodromal fracture pathology was observed in 15/110 (14%) limbs with parasagittal fractures, and in 4% of contralateral limbs.

CONCLUSIONS:

The results of this study are not consistent with monotonic loading as a cause of fracture in at least a proportion of cases, but suggest a stress related aetiology. Increased thickness of the subchondral bone plate may reflect (failed) adaptive changes that precede fracture. POTENTIAL RELEVANCE: Better understanding of the aetiology of fractures of the proximal phalanx may help develop strategies to reduce the risk of fracture.

REASONS FOR PERFORMING STUDY: Hypoxia inducible factor-1α (HIF-1A) is an important protein in the regulation/induction of many genes in the cellular and tissue response to hypoxia and a central mediator in inflammatory signaling. As both hypoxia and inflammatory events are purported to occur in the lamellar epidermis in sepsis-related laminitis in the equid, HIF-1A may play a central role in this disease process.

OBJECTIVE:

To assess the regulation of HIF-1A and HIF-1A-related genes in the equine keratinocyte in vitro, and in the lamellar tissue of horses with sepsis-related laminitis.

STUDY DESIGN:

In vitro experiment.

METHODS:

Real time-quantitative PCR (RT-qPCR) and immunoblotting were performed to assess the mRNA and protein concentrations of HIF-1A and mRNA concentrations of HIF-1A-related genes in cultured equine keratinocytes and in lamellar samples from the black walnut extract (BWE)- and carbohydrate overload (CHO)-induced laminitis. HIF-1A was further localised via indirect immunofluorescence in frozen lamellar tissue sections.

RESULTS:

HIF-1A appears to be primarily regulated at the post-transcriptional level in the cultured equine keratinocyte, resulting in increased HIF-1A in response to hypoxia but not to LPS exposure. HIF-1A is present at high concentrations in the normal equine lamina, and is increased in OG1 stage laminitis in the CHO model of laminitis. Equine lamellar mRNA concentrations of COX-2 and NOS2, but not GLUT1, are increased in the BWE and CHO models of laminitis.

CONCLUSIONS

AND POTENTIAL RELEVANCE: These data indicate that the normal equine lamellae are profoundly hypoxic compared to other tissues. The increased mRNA concentrations of COX-2 and NOS2 in equine keratinocytes exposed to hypoxia and LPS, and in lamellar tissue from BWE and CHO models of sepsis-related laminitis, suggest that the marked lamellar inflammatory gene expression in sepsis-related laminitis may be due to an interaction of constitutively high lamellar keratinocyte HIF-1A signaling with inflammatory signaling possibly induced by circulating inflammatory mediators.

REASONS FOR PERFORMING STUDY: Incisional complications following exploratory celiotomy increase morbidity, extend hospitalisation, and increase cost. Retrospective studies seek to identify risk factors and measures for prevention of surgical site infection. The relatively high incidence of incisional complications following exploratory laparotomy necessitates identification of ideal surgical closure methods.

OBJECTIVES:

The study sought to identify the incidence of incisional drainage within our hospital population, and to identify risk factors for incisional complications while determining surgical practices that reduce the incidence of incisional drainage.

STUDY DESIGN:

Retrospective cohort study.

METHODS:

A retrospective study, with telephone follow-up, was performed on 199 horses that underwent exploratory laparotomy at the University of Georgia from 1 January 2008 - 31 December 2010, examining associations between signalment, lesion type, access to the lumen of the bowel, and closure methods and incisional draining. The linea alba incisions were closed by the primary surgeon and junior house officers closed the subcutaneous tissues and skin.

RESULTS:

The incidence of purulent or persistent serosanguinous incisional drainage in 142 horses with complete follow-up information was 21.8%. Signalment, lesion type, and enterotomy or enterectomy were not associated with a significantly increased likelihood of incisional drainage. However, closure of the subcutaneous tissues and skin in a two-layer, modified subcuticular pattern was associated with a significantly lower incidence of post-operative incisional drainage. Follow-up information identified subsequent episodes of colic in 28.9% of horses. However, 80.3% of horses had returned to their previous level of work.

CONCLUSIONS

AND POTENTIAL RELEVANCE: Incisional drainage is common following ventral midline laparotomy. The use of a two-layer, modified subcuticular closure was associated with a significant reduction in the incidence of incisional drainage compared to closure performed with skin sutures, but not closure performed with staples.

REASONS FOR PERFORMING STUDY: Plasma fructosamine concentration ([fructosamine]) is believed to reflect medium term, average blood glucose concentration and in a previous study was higher in horses with active laminitis than in normal horses. Pituitary pars-intermedia dysfunction (PPID) is associated with hyperglycaemia and laminitis.

OBJECTIVES:

To test the hypotheses that: [fructosamine] is higher in PPID cases than normal animals; furthermore, that within cases of PPID [fructosamine] is higher in those with active laminitis than non-laminitic cases, and in cases that have been affected by active laminitis in the preceding year than those that have not.

STUDY DESIGN:

Observational, case control/cross sectional study.

METHODS:

[Fructosamine] was measured in cases of PPID (n = 46) and normal animals (n = 139). A normal range was calculated; values were compared between the 2 groups, and, within the PPID group, between cases with and without active laminitis, and between cases which had and had not been affected by active laminitis in the preceding year.

RESULTS:

In normal animals mean [fructosamine] was 248.7 μmol/l; the normal range (mean + 2 s.d.) was 195.5-301.9 μmol/l. Plasma [fructosamine] was not higher in PPID cases than in normal animals. In PPID cases, [fructosamine] was significantly (p = 0.006) higher in cases with active laminitis (mean + s.d. 261.2 + 39.2 μmol/l) compared with those without active laminitis (234.5 + 32.9 μmol/), but [fructosamine] was not higher in cases that had been affected by active laminitis in the preceding year than those which had not.

CONCLUSIONS:

In horses affected by PPID, [fructosamine] is higher in cases with active laminitis than in cases without active laminitis. POTENTIAL RELEVANCE: Clinical use of [fructosamine] is limited due to overlap with the normal range. Further studies into glucose and protein metabolism in cases of PPID are warranted.

REASONS FOR PERFORMING THE STUDY: Severe hypertriglyceridaemia in horses and ponies with endocrine disorders has been reported anecdotally but has not been documented in the literature.

OBJECTIVES:

To describe historical and clinicopathological findings as well as progression and outcome in horses and ponies with severe hypertriglyceridaemia (serum triglyceride concentration >5.65 mmol/l) secondary to an endocrine disorder that were otherwise apparently healthy.

METHODS:

Cases from 6 participating institutions were identified and case details extracted from the medical records.

RESULTS:

Case details of 3 horses and 4 ponies were available. Presenting complaints included weight loss despite good appetite in 4 animals while in 3 hypertriglyceridaemia was identified incidentally. All animals were bright and alert and showed a normal or increased appetite. Serum triglyceride concentrations ranged from 10.5-57.9 mmol/l. Other abnormalities included hyperglycaemia in 6 animals, suspected insulin resistance and mild to severe increases in hepatic enzyme activities. In 2 animals moderate hepatic lipidosis was confirmed histologically. Three horses and 3 ponies were diagnosed with pituitary pars intermedia dysfunction (PPID) based on clinical signs and basal ACTH concentrations or dexamethasone suppression test results. In 5 of these, type II diabetes mellitus was also confirmed while one pony suffered from type II diabetes mellitus without concurrent PPID. Laboratory abnormalities improved in 4 animals with treatment (pergolide and/or insulin), in one horse specific treatment was not attempted and in 2 ponies treatment was impaired by the owner or only partially effective. In one of the latter cases biochemical abnormalities persisted for 7 years without apparent ill effects.

CONCLUSIONS

AND POTENTIAL RELEVANCE: Horses and ponies may develop severe hypertriglyceridaemia secondary to endocrine disorders that are associated with insulin resistance. Hypertriglyceridaemia can resolve with treatment of the endocrinopathy. Although biochemical evidence of hepatic compromise was present, clinical abnormalities were not noted in these animals.