Implementation of a prototype dynamic laryngoplasty system in standing sedated horses provided arytenoid abduction control at seven days postoperatively.

OBJECTIVE: Evaluate a prototype dynamic laryngoplasty system (DLPS) in horses; a feasibility study. ANIMALS: 7 healthy Standardbred adult horses. METHODS: This was an in vivo experimental study. Horses had a standing surgical procedure to induce complete laryngeal hemiplegia, which was subsequently treated using the dynamic laryngoplasty system (DLPS). Activation of the DLPS was achieved using an injection port exiting through the skin (n = 2) or a subcutaneous injection port (n = 5). For each horse, endoscopic examinations of the upper respiratory tract were performed preoperatively, intraoperatively, and 7 days postoperatively. Left-to-right quotient ratios calculated during inactivated and activated states were obtained from still images of the rima glottidis acquired during day 7. In 3 horses, the device was intentionally overinflated to evaluate for device failure, and postmortem examinations were performed on day 7. For the remaining 4 horses, upper respiratory tract endoscopy was repeated at 1 month postoperatively, with no subsequent postmortem exam. RESULTS: No perioperative complications occurred, and the DLPS was effectively delivered in all horses under standing sedation. The left-to-right quotient ratio at day 7 postoperatively could be altered from a resting position of 0.76 (± 0.06) to a maximum of 0.97 (± 0.06; P < .05). The degree of arytenoid abduction could not be significantly altered after 1 month of device implantation, suspected to be due to peri-implant fibrosis. No coughing nor tracheal contamination was observed at all time points or during inflation. CLINICAL RELEVANCE: The ability to alter the degree of abduction at 7 days postoperatively with the DLPS may be beneficial in selective cases.

The effect of pre-dosing with metformin on the insulin response to oral sugar in insulin-dysregulated horses.

BACKGROUND: A single dose of metformin administered 1 h prior to oral glucose challenge was previously shown to reduce insulinaemic responses in horses with experimentally-induced insulin dysregulation (ID). Targeted administration could be useful for controlling post-prandial hyperinsulinaemia in horses with naturally-occurring ID. OBJECTIVES: The objective was to compare the insulinaemic and glycaemic responses to oral sugar testing (OST) performed at different intervals after a single dose of metformin in horses with naturally-occurring ID. We hypothesised that pre-treatment with one dose of metformin would significantly decrease the insulinaemic response to OST. STUDY DESIGN: Randomised cross-over in vivo experiment. METHODS: Eight university-owned adult horses with naturally-occurring ID underwent OST 1, 2 and 6 h following a single oral dose of metformin (30 mg/kg) or 1 h after placebo (240 mL water) with a 7-day washout between treatments over a period of 3 weeks. Plasma insulin, C-peptide and glucose concentrations were measured at 0, 60 and 90 min after 0.45 mL/kg light corn syrup and the effect of treatment (and the interval since dosing) examined using a mixed effects linear regression model. RESULTS: Metformin treatment had no significant effect on plasma glucose, insulin or C-peptide concentrations at any time point compared with placebo (p > 0.05). For OST 1 h post metformin, median (IQR) plasma insulin was 91.3 (62.4-114.9) µIU/mL at 60 min versus 76.2 (59.1-134.5) for placebo (p = 0.8) and 62.7 (31.4-109.7) at 90 min versus 51.8 (29.2-126.3) for placebo (p = 0.9). MAIN LIMITATIONS: Small sample size may limit identification of more subtle decreases in insulin concentration with metformin pre-dosing. The results of this study are relevant only for one pre-treatment dose (30 mg/kg) which limits extrapolation to predictions about the effects of longer-term metformin administration on insulin and glucose dynamics in the horse. CONCLUSIONS AND CLINICAL IMPORTANCE: The results do not support the use of targeted metformin treatment to reduce post-prandial hyperinsulinaemia in horses with naturally-occurring ID.

The influence of different horseshoes and ground substrates on mid-stance hoof orientation at the walk.

BACKGROUND: Horseshoes with modified contact surfaces combined with deformable ground substrates are used to change hoof orientation during mid-stance, for example, for therapeutic reasons. OBJECTIVES: To measure the effect of horseshoes and ground substrates on sagittal and transverse plane hoof orientation at mid-stance using a dorsal hoof wall mounted triaxial accelerometer. STUDY DESIGN: In vivo experiment, randomised crossover design. METHODS: Differences in sagittal and transverse plane angles between standing and mid-stance of the left front hoof of six horses walking with regular horseshoes, egg bar, toe-wide, medial-wide, lateral-wide and three-degree egg bar shoes on turf, sand and hard ground substrates were assessed with linear mixed models with horseshoe and substrate type as fixed factors (p < 0.05) for each animal. RESULTS: Hoof angles were significantly affected by horseshoe (p < 0.001), surface (p < 0.001) and the combination (p < 0.001). The sagittal plane angle increased in deformable ground substrates at walk-in mid-stance on turf [mean (±standard deviation): 2.6° (±3.8°)] and on sand [2.6° (±4.1°)] across all shoes. The greatest increase was observed with egg bar shoes [turf: 4.37° (±3.82°); sand 4.69° (±3.83°)]. There was a tendency for the hoof to sink laterally into deformable ground substrates among all shoes [turf: 1.11° (±1.49°); sand: 0.93° (±1.93°)]. Medial-wide shoes increased the lateral sinking [turf: 2.00° (±1.63°); sand: 1.79° (±1.58°)]. Lateral-wide shoes reduced the lateral sinking on turf [0.62° (±1.26°)] and induced a marginal medial sinking on sand [-0.007° (±2.03°)]. MAIN LIMITATIONS: The substrate properties were not quantitatively assessed, and observations were limited to front hooves at the walk. A larger sample size would be preferable. CONCLUSIONS: Mid-stance hoof orientation changes with specific combinations of shoes and ground substrates in the walking horse.

CONTEXTO: É especulado que ferraduras com solados diferentes combinadas com superfícies deformáveis podem mudar a orientação do casco durante a fase de apoio, por exemplo, por razões terapêuticas. OBJETIVOS: Mensurar o efeito de diferentes ferraduras e superfícies na orientação do casco nos planos sagital e transversal durante a fase de apoio usando um acelerômetro triaxial acoplado à parte dorsal do casco. DELINEAMENTO DO ESTUDO: Experimento in vivo, delineamento randomizado e cruzado. MÉTODOS: As diferenças entre os ângulos dos planos sagital e transverso nas diferentes fases de apoio do casco do membro anterior esquerdo de seis cavalos ao passo utilizando ferradura normal, oval, oval talonada, de pinça larga e com extensão medial ou lateral na grama, areia ou superfície dura foram avaliadas utilizando modelos mistos lineares com ferradura e tipo de superfície como fatores fixos (P < 0.05) para cada animal. RESULTADOS: Os ângulos do casco foram significativamente afetados pelo tipo de ferradura (P < 0.001), superfície (P < 0.001) e pela combinação de ambos (P < 0.001). O ângulo do plano sagital aumentou em superfícies deformáveis no passo na fase de apoio na grama (média (+/-SD): 2.6 (+/−3.8) graus) e na areia (2.6 (+/−4.1 graus) para todos os tipos de ferradura. O maior aumento foi observado com a ferradura oval (grama: 4.37 (+/− 3.82) graus; areia 4.69 (+/−3.83) graus). Houve uma tendência de o casco rebaixar mais lateralmente em superfícies deformáveis com todas as ferraduras (grama: 1.11 (+/−1.49) graus; areia: 0.93 (+/−1.93) graus). Ferraduras com extensão medial aumentaram o rebaixamento lateral (grama: 2.00 (+/−1.63) graus; areia: 1.79 (+/−1.58) graus). Ferraduras com extensão lateral reduziram o rebaixamento lateral na grama (0.62 (+/−1.26) graus) e induziram o rebaixamento medial na areia (−0.007 (+/−2.03) graus). PRINCIPAIS LIMITAÇÕES: As propriedades das superfícies não foram avaliadas quantitativamente, e as observações foram limitadas aos cascos dos membros anteriores e ao passo. Um número maior de animais no estudo seria desejável. CONCLUSÕES: A orientação do casco na fase de apoio muda de acordo com combinações específicas de ferradura e superfícies no cavalo ao passo.

The effects of orally administered trazodone on ambulation and recumbency in healthy horses.

BACKGROUND: Trazodone, a serotonin receptor antagonist and reuptake inhibitor, might be a useful adjunctive treatment in the initial management of horses with acute laminitis if it minimizes ambulation or encourages recumbency. OBJECTIVES: (1) Evaluate the effects of PO trazodone on ambulatory activity and recumbency in healthy horses; and (2) assess the pharmacokinetics of multiple PO doses of trazodone. ANIMALS/METHODS: In a randomized cross-over design, 8 healthy horses received placebo or trazodone at 2 doses (2.5 and 7.5 mg/kg) PO q12h for 48 hours with a 14-day washout period between treatments. Forelimb step frequency was measured using a hoof-mounted accelerometer and continuous video monitoring was used to detect recumbency. Groups were compared using repeated measures analysis of variance with Tukey's post hoc test. Trazodone and m-chlorophenylpiperazine (m-CPP) plasma concentrations were determined by ultra-high performance liquid chromatography-tandem mass spectrometry and pharmacokinetics were analyzed using noncompartmental methods. RESULTS: Step frequency was lower in horses receiving 7.5 mg/kg trazodone than in the control group (mean step reduction: 44% ± 11%). Steps-area under the curve were significantly lower in the 7.5 mg/kg group (mean ± SD: 3375 ± 525 steps × hour) as compared to the 2.5 mg/kg group (mean ± SD: 5901 ± 2232; P = .02) and compared to control (mean ± SD: 6590 ± 1241; P = .001). No difference was found in the number of recumbent episodes (P = .92) or total duration of recumbency (P = .9). Trazodone and m-CPP achieved steady-state concentrations, with an accumulation ratio of 1.45 ± 0.2. CONCLUSIONS AND CLINICAL IMPORTANCE: Although it did not affect recumbency, trazodone at 7.5 mg/kg q12h decreased step frequency by approximately 44%.

Effect of ambulation following 18F-fluorodeoxyglucose injection on standing positron emission tomography of the healthy equine digit.

OBJECTIVE: Measure 18F-FDG uptake in digital tissues of healthy horses subjected to different ambulatory conditions between the time of injection and positron emission tomography (PET) scan acquisition. ANIMALS: 8 healthy adult horses. METHODS: Horses were walked (AMB) or tied in stalls (NONAMB) immediately after injection with ∼1.5 MBq/kg 18F-FDG until scan acquisition using a randomized crossover design. Steps were quantified using accelerometers. Standardized uptake values (SUV; mean and maximum) in digital tissues including the dorsal lamellae (proximal, middle, and distal), quarter lamellae (medial and lateral), and coronary band were analyzed using a mixed-effects linear regression model. RESULTS: Mean (95% CI) step count for AMB (569[484-653]) was higher than NONAMB (88[24-152]) P = <.001. The SUVmax (but not SUVmean) was increased in AMB compared with NONAMB in the proximal (2.74[2.52-2.98] vs 2.42[2.05-2.78]; P = .04) and middle (2.74[2.37-3.11] vs 2.36[2.05-2.68]; P = .03) dorsal lamellae but was not different in the distal lamellae or coronary band. In the medial quarter lamellae, both SUVmax (2.53[1.58-3.48] vs 2.07[0.81-3.33]; P = .01) and SUVmean (1.90[1.55-2.25] vs 1.49[0.91-2.06]; P = .007) were increased in AMB compared with NONAMB. The medial quarter lamellae also had lower SUVmax (P = .002) and SUVmean (P = .04) compared with the lateral quarter and lower SUVmax compared with the mid-dorsal lamellae (P = .01). CLINICAL RELEVANCE: Lamellar 18F-FDG uptake was affected by ambulatory activity mostly in the medial quarter; however, this effect was relatively small and unlikely to interfere with clinical detection of laminitis.

Digital lamellar inflammatory signaling in an experimental model of equine preferential weight bearing.

BACKGROUND: Supporting limb laminitis (SLL) is a complication of severe orthopedic disease in horses and is often life-limiting, yet the pathophysiology remains obscure. HYPOTHESIS/OBJECTIVES: To investigate the role of digital lamellar inflammatory signaling in the pathophysiology of SLL using a model of unilateral weight bearing, hypothesizing that there would be evidence of lamellar inflammation in limbs subjected to the model. ANIMALS: Thirteen healthy adult Standardbred horses were used for this study (11 geldings, 2 mares; mean age 6.5 ± 2.5 years; mean body weight 458.3 ± 32.8 kg). METHODS: Randomized controlled experimental study. A steel shoe with a custom insert was applied to a randomly selected front foot of 7 horses; 6 horses were unshod and served as controls. After 92 hours, all horses were humanely euthanized, and digital lamellar samples were collected. Lamellar protein and mRNA were isolated and used to perform western blot and PCR. RESULTS: Lamellar concentrations of IL-6 mRNA were higher in SL tissue than IL HIND tissue (median [25%-75%] normalized copy number 191 [111-3060] and 48 [25-74], respectively; P=.003), and lamellar concentrations of COX-2 mRNA were higher in SL tissue than CON tissue (normalized copy number 400 [168-634] and 125 [74-178], respectively; P=.007). Lamellar concentrations of IL-1B, IL-10, and COX-1 mRNA were not significantly different between groups. The concentrations of phosphorylated (activated) STAT1 and STAT3 proteins were higher in SL (0.5 [0.35-0.87] and 1.35 [1.1-1.7], respectively) compared to CON (0.24 [0.09-0.37] and 0.31 [0.16-037]) and UL HIND (0.27 [0.19-0.37] and 0.38 [0.24-0.5]); P=0.01 and P<0.001. CONCLUSIONS AND CLINICAL IMPORTANCE: Lamellar inflammatory signaling was higher in tissue from horses subjected to prolonged unilateral weight-bearing, suggesting that these pathways could be relevant to the pathophysiology of SLL.

Effect of sirolimus on insulin dynamics in horses.

BACKGROUND: Sirolimus, a mechanistic target of rapamycin inhibitor, suppresses insulin production in other species and has therapeutic potential for hyperinsulinemia in horses. HYPOTHESIS/OBJECTIVE: Determine the pharmacokinetics (PKs) of sirolimus and evaluate its effect on insulin dynamics in healthy and insulin dysregulation (ID) horses. ANIMALS: Eight Standardbred geldings. METHODS: A PK study was performed followed by a placebo-controlled, randomized, crossover study. Blood sirolimus concentrations were measured by liquid chromatography-mass-spectrometry. PK indices were estimated by fitting a 2-compartment model using nonlinear least squares regression. An oral glucose test (OGT) was conducted before and 4, 24, 72, and 144 hours after administration of sirolimus or placebo. Effects of time, treatment and animal on blood glucose and insulin concentrations were analyzed using mixed-effects linear regression. Sirolimus was then administered to 4 horses with dexamethasone-induced ID and an OGT was performed at baseline, after ID induction and after 7 days of treatment. RESULTS: Median (range) maximum sirolimus concentration was 277.0 (247.5-316.06) ng/mL at 5 (5-10) min and half-life was 3552 (3248-4767) min. Mean (range) oral bioavailability was 9.5 (6.8-12.4)%. Sirolimus had a significant effect on insulin concentration 24 hours after a single dose: median (interquartile range) insulin at 60 min (5.0 [3.7-7.0] µIU/mL) was 37 (-5 to 54)% less than placebo (8.7 [5.8-13.7] µIU/mL, P = .03); and at 120 min (10.2 [8.4-12.2] µIU/mL) was 28 (-15 to 53)% less than placebo (14.9 [8.4-24.8] µIU/mL, P = .02). There was minimal effect on glucose concentration. Insulin responses decreased toward baseline in ID horses after 7 days of treatment. CONCLUSION AND CLINICAL IMPORTANCE: Sirolimus decreased the insulinemic response to glucose and warrants further investigation.

The effect of cyanoacrylate on knot elongation in three sutures used for prosthetic laryngoplasty in the horse.

OBJECTIVE: This study investigated the elongation following cyclic loading on square knots of 5 USP multifilament long-chain ultra-high molecular weight polyethylene core (UHMWPE), 2 mm woven UHMWPE tape, and 5 USP braided polyester, with and without cyanoacrylate glue. STUDY DESIGN: Experimental study. SAMPLE POPULATION: n = 4. METHODS: Three conditions (suture without knot, suture with knot, suture with knot + cyanoacrylate) were evaluated for each suture material on a mechanical test stand by measuring the increased length of the construct after cycling from 25 to 50N for 1000 repetitions at 20 mm/second. Knot elongation was determined by subtracting the length of the control suture from the suture with knot or suture with knot + cyanoacrylate. The data were analyzed with a linear regression model with robust estimation of variance. Post-hoc analysis determined the model adjusted differences (square knot vs. cyanoacrylate) as a difference from control. t-tests were conducted to identify the significant findings. RESULTS: Total elongation of polyester (6.2-7.8 mm) was greater than multifilament UHMWPE (3.4-6.4 mm) and UHMWPE tape (2-3.7 mm) for all conditions. Polyester had the lowest knot elongation (1.6 mm) and the addition of cyanoacrylate decreased knot elongation for polyester by 1 mm. CONCLUSIONS: Polyester had the most total construct elongation followed by multifilament UHMWPE and UHMWPE tape. Polyester showed the least knot elongation and cyanoacrylate decreased this knot elongation. CLINICAL SIGNIFICANCE: Total construct and knot elongation should be considered as contributing factors to loss of arytenoid abduction following prosthetic laryngoplasty when using polyester, multifilament UHMWPE, or UHMWPE tape. Addition of cyanoacrylate to polyester knots should be explored to limit elongation.

Evaluation of locking compression plate fixation of the distal phalanx to the hoof wall as a potential therapy for laminitis.

BACKGROUND: Surgical stabilisation of the distal phalanx (DP) is a potential therapeutic strategy for severe acute laminitis. OBJECTIVE: To evaluate the effects of locking compression plate (LCP) fixation of the DP to the dorsal hoof wall. STUDY DESIGN: Ex vivo and in vivo experiments. METHODS: A T-shaped LCP was applied to one limb per pair in six pairs of cadaver forelimbs subjected to a combination of thermally induced lamellar failure and vertical load to simulate severe acute laminitis. Standard radiographic measurements were used to compare DP displacement. The LCP was then applied to one forefoot in 12 healthy Standardbred horses either standing (n = 6) or under general anaesthesia (n = 6). Lameness was evaluated daily, then horses were euthanised (day 8) and lamellar tissue analysed using light microscopy, histomorphometery and molecular markers of apoptosis. RESULTS: In the cadaver limb model, LCP fixation prevented the significant changes in hoof-distal phalanx distance, coronary extensor process distance and sole depth that characterised DP displacement in untreated limbs (p < 0.05). Application of the construct in vivo was well tolerated with minimal lameness (10/12 horses were sound at the trot on day 8); however, histology revealed dorsal lamellar pathology consistent with laminitis, but with extensive keratinocyte apoptosis. Adjacent to the LCP, caspase-3 positive cell counts were approximately 20-fold higher than control (p < 0.001). MAIN LIMITATIONS: Pathology was evaluated at a single time point. Microvascular perfusion was not evaluated. CONCLUSIONS: Rigid fixation of the DP to the hoof capsule was achieved with the LCP construct in a cadaver limb laminitis model. In live horses, LCP fixation caused regional lamellar pathology with extensive apoptosis, likely due to disturbed lamellar microvascular perfusion and/or mechanostasis. Understanding these mechanisms is critical for refinement of the technique in order to avoid iatrogenic lamellar damage.

Effect of a GLP-1 mimetic on the insulin response to oral sugar testing in horses.

BACKGROUND: Insulin dysregulation (ID) is the most important risk factor for the development of laminitis in horses and therapies to control it are needed. HYPOTHESIS/OBJECTIVES: To assess the effects of a single dose of the synthetic GLP-1 analog exenatide on postprandial insulin dynamics. We hypothesized that exenatide would improve insulin sensitivity and lower postprandial blood insulin concentrations. STUDY DESIGN: Randomized, crossover, experimental study. ANIMALS: Six horses (3 mares, 3 geldings; 2 with normal insulin regulation [NIR] and 4 with mild ID). METHODS: Horses completed both study arms: subcutaneous administration of exenatide (or no treatment) 30 min before an oral sugar test (0.15 ml/kg of Karo Syrup). Blood samples obtained over 240 min were assayed for glucose, insulin, lactate, c-peptide and total GLP-1. The area under the curve (AUC) was calculated using the trapezoidal rule. Insulin sensitivity (SI) was estimated using a mathematical model. RESULTS: Exenatide resulted in a postprandial decrease of 20% (effect size: 2673 µU·min/ml; 95% CI: 900 - 4446 µU·min/ml; P = 0.003) in AUC of plasma insulin (control; mean AUC insulin: 11,989 µU·min/ml; 95% CI: 9673 - 14,305 µU·min/ml, exenatide; mean AUC insulin: 9316 µU·min/ml; 95% CI: 7430 - 11,202 µU·min/ml). Exenatide resulted in an approximately threefold increase (effect size: 5.56 10-4· µU/ml-1·min-1; 95% CI: 0.95 - 10.1 10-4· µU/ml-1·min-1; P = 0.02) in estimated insulin sensitivity (control mean SI: 1.93 10-4· µU/ml-1·min-1; 95% CI: 0.005 - 3.86 10-4·µU/ml-1·min-1 vs. exenatide mean SI: 7.49 10-4· µU/ml-1·min-1; 95% CI: 3.46 - 11.52 10-4· µU/ml-1·min-1). CONCLUSIONS: The decrease in insulin response to carbohydrates was due to an increase in whole-body insulin sensitivity. GLP-1 agonists may have therapeutic potential for ID in horses.

Treatment of primary hyperparathyroidism in a Miniature Horse using chemical ablation of abnormal parathyroid tissue localized by 3-phase computed tomography.

A 15-year-old Miniature Horse mare with persistently increased plasma calcium (total and ionized) and serum parathyroid hormone concentrations was presented for suspected primary hyperparathyroidism. Ultrasonography of the thyroid region identified an enlarged heterogeneous mass axial to the right thyroid lobe suggestive of an enlarged parathyroid gland, which was further confirmed using sestamibi nuclear scintigraphy and 3-phase computed tomography. Percutaneous ultrasound-guided ethanol ablation of the mass, a method not previously described in the horse, was performed under general anesthesia resulting in rapid normalization of plasma ionized calcium and serum parathyroid hormone concentrations. Ablation of abnormal parathyroid gland tissue may be a suitable alternative to surgical resection in certain cases of primary hyperparathyroidism in the horse.

Supporting Limb Laminitis.

Supporting limb laminitis (SLL) is a relatively frequent complication of painful limb conditions that alter normal weight-bearing patterns in horses. New evidence suggests that a lack of limb load cycling activity (normally associated with ambulation) interferes with normal perfusion of the lamellae in these cases, resulting in ischemia and dysfunction/death of cells critical to the mechanical function of the lamellae. Excessive weight-bearing load drives the progression to overt acute laminitis in the supporting limb. Monitoring and enhancement of limb load cycling activity are key strategies that may lead to successful prevention of SLL by ensuring adequate lamellar perfusion.

Continuous digital hypothermia reduces expression of keratin 17 and 1L-17A inflammatory pathway mediators in equine laminitis induced by hyperinsulinemia.

The euglycemic hyperinsulinemic clamp model (EHC) of equine endocrinopathic laminitis induces rapid loss of lamellar tissue integrity, disrupts keratinocyte functions, and induces inflammation similar to natural disease. Continuous digital hypothermia (CDH) blocks tissue damage in this experimental model, allowing identification of specific genes or molecular pathways contributing to disease initiation or early progression. Archived lamellar tissues (8 horses, 48 h EHC treatment, including CDH-treated front limbs) were used to measure relative expression levels of genes encoding keratin 17 (KRT17), a stress-induced intermediate filament protein, and genes upregulated downstream of keratin 17 and/or interleukin 17A (IL-17A), as mediators of inflammation. Compared to front or hind limbs at ambient temperature, CDH resulted in significantly lower expression of KRT17, CCL2, CxCL8, PTGS2 (encoding COX2), IL6, TNFα, S100A8 and MMP1. By immunofluorescence, COX2 was robustly expressed in lamellar keratinocytes from ambient limbs, but not in CDH-treated limbs. Genes not significantly reduced by CDH were IL17A, DEFB4B, S100A9 and MMP9. Overall, 8 of 12 genes were expressed at lower levels in the CDH-treated limb. These 8 genes are expressed by wounded or stress-activated keratinocytes in human disease or mouse models, highlighting the role of keratinocytes in equine laminitis.

Plasma amino acid concentrations during experimental hyperinsulinemia in 2 laminitis models.

BACKGROUND: Endocrinopathic laminitis develops in association with insulin dysregulation, but the role of insulin in the pathogenesis remains unclear. Hyperinsulinemia can cause hypoaminoacidemia, which is associated with integumentary lesions in other species and therefore warrants investigation as a potential mechanism in laminitis. OBJECTIVE: Evaluate plasma amino acid concentrations in the euglycemic-hyperinsulinemic clamp (EHC) and prolonged glucose infusion (PGI) laminitis models. ANIMALS: Sixteen Standardbred horses. METHODS: Prospective experimental study. Plasma amino acid concentrations were measured in samples collected every 6 hours from horses that underwent a 48-hour EHC (n = 8) or 66-hour PGI (n = 8) after a 24- or 6-hour baseline period in EHC and PGI groups, respectively. RESULTS: Fifteen of the 20 measured amino acid concentrations decreased over time in both EHC and PGI horses (P < 0.001). The median percentage change from baseline for these amino acids was: histidine (EHC: 41.5%; PGI: 43.9%), glutamine (EHC: 51.8%; PGI: 35.3%), arginine (EHC: 51.4%; PGI: 41%), glutamic acid (EHC: 52.4%; PGI: 31.7%), threonine (EHC: 62.8%; PGI: 25.2%), alanine (EHC: 48.9%; PGI: 19.5%), proline (EHC: 56.2%; PGI: 30.3%), cystine (EHC: 34.9%; PGI: 31.2%), lysine (EHC: 46.4%; PGI: 27.8%), tyrosine (EHC: 27.5%; PGI: 16.9%), methionine (EHC: 69.3%; PGI: 50.8%), valine (EHC: 50.8%; PGI: 34.4%), isoleucine (EHC: 60.8%; PGI: 38.7%), leucine (EHC: 48.2%; PGI: 36.6%), and phenylalanine (EHC: 16.6%; PGI: 12.1%). CONCLUSIONS AND CLINICAL IMPORTANCE: Hypoaminoacidemia develops in EHC and PGI laminitis models. The role of hypoaminoacidemia in the development of hyperinsulinemia-associated laminitis warrants further investigation.

Lamellar perfusion and energy metabolism in a preferential weight bearing model.

BACKGROUND: Supporting limb laminitis (SLL) is suspected to be caused by lamellar ischaemia as a consequence of increased mechanical load. OBJECTIVES: Examine the effects of prolonged preferential weight bearing (PWB) on lamellar perfusion and metabolism. STUDY DESIGN: In vivo experiment. METHODS: Microdialysis probes were inserted in the lamellar and sublamellar dermis of one forelimb in 13 Standardbred horses. In six horses, a platform shoe (contralateral forelimb) was used to induce increased load on the microdialysis-instrumented forelimb (PWB). The remaining seven horses were controls (CON). All horses were housed in stocks with limb weight distribution logged continuously for 92 hours. Microdialysate was collected and analysed every 4 hours for glucose, lactate, pyruvate, and lactate to pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar perfusion. Data were analysed using a mixed-effects linear regression model. RESULTS: Median [IQR] load on the microdialysis-instrumented limb was equivalent to 38.7% bwt. [37.3-40.3] in PWB and 27.3% bwt. [26.6-28] in CON. Limb offloading frequency increased in CON (P < .001) but not PWB (P = .2). Lamellar microdialysate glucose decreased in PWB (P < .001) and CON (P = .004), however, the rate of decrease was higher in PWB (P = .007). Lamellar L:P increased in PWB (P < .001) and peaked at 196 [79-656], whereas L:P did not change over time in CON (P = .6) and peaked at 42 [41-49]. Lamellar urea clearance decreased in PWB (P < .001) but not in CON (P = .3). Sublamellar L:P and urea clearance did not change over time in either group (P > .05). MAIN LIMITATIONS: The PWB model may not be representative of naturally occurring SLL. CONCLUSIONS: Evidence of lamellar ischaemia (increased L:P and decreased urea clearance) was detected exclusively in the lamellar dermis of PWB feet subjected to persistently increased load. Lamellar ischaemia is a consequence of increased mechanical load and likely contributes to the development of SLL.

Effect of digital hypothermia on lamellar inflammatory signaling in the euglycemic hyperinsulinemic clamp laminitis model.

BACKGROUND: Continuous digital hypothermia (CDH) prevents lamellar failure in the euglycemic hyperinsulinemic clamp (EHC) model of laminitis, but the protective mechanisms are unclear. HYPOTHESIS/OBJECTIVES: To determine if CDH inhibits lamellar inflammatory signaling in the EHC model of laminitis. ANIMALS: Eight Standardbred horses. METHODS: Prospective experimental study. Horses underwent an EHC, with 1 forelimb treated with CDH and the other kept at ambient temperature (AMB). Horses were euthanized 48 hours after initiation of the EHC and lamellar tissue was analyzed via polymerase chain reaction (pro-inflammatory cytokine and chemokine genes-CXCL1, CXCL6, CXCL8, IL-6, MCP-1, MCP-2, IL-1ß, IL-11, cyclooxygenase 1 and 2, tumour necrosis factor-alpha [TNF-α], E-selectin, and intercellular adhesion molecule-1 [ICAM-1]) and immunoblotting (phosphorylated and total signal transducer and activator of transcription 1 [STAT1] and STAT3). RESULTS: Compared to AMB, lamellar messenger ribonucleic acid (mRNA) concentrations of CXCL6 (P =.02), CXCL8 (P = .008), IL-6 (P = .008), IL-1ß (P = .008), IL-11 (P = .008), and cyclooxygenase-2 (P = .008) were decreased in CDH. Cyclooxygenase-1 (P = .008) was increased in CDH, while CXCL1 (P = .15), MCP-1 (P = .05), MCP-2 (P = .46), TNF-α (P = .05), E-selectin (P = .15), and ICAM-1 (P = .15) mRNA were not significantly different. Compared to AMB, lamellar concentration of total STAT3 protein was decreased in CDH (P < .001), but there was no change in phosphorylated STAT3 (P-STAT3 [S727] P = .19; P-STAT3 [Y705] P = .05). There was no change in lamellar concentrations of total STAT1 (P = .75) or phosphorylated STAT1 (P-STAT1 [S727], P = .25; P-STAT1 [Y701], P = .64). CONCLUSIONS AND CLINICAL IMPORTANCE: These data add further support for the use of CDH as a first aid treatment for severe acute laminitis associated with hyperinsulinemia in horses.

The effect of continuous digital hypothermia on lamellar energy metabolism and perfusion during laminitis development in two experimental models.

BACKGROUND: Continuous digital hypothermia (CDH) prevents lamellar failure in the euglycaemic hyperinsulinaemic clamp (EHC) and oligofructose (OF) laminitis models, but the mechanisms remain unclear. OBJECTIVES: To evaluate the effects of CDH on lamellar energy metabolism and perfusion in healthy horses and during EHC and OF laminitis models. STUDY DESIGN: In vivo experiment. METHODS: Archived samples were used from Standardbred geldings that received no treatment (CON) (n = 8) or underwent EHC (n = 8) or OF (n = 6) laminitis models. Both forelimbs were instrumented with a lamellar microdialysis system, and one forelimb was cooled (CDH) with the other maintained at ambient temperature (AMB). Microdialysate was collected every 6 hours and analysed for glucose, lactate and pyruvate concentrations and lactate to pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar tissue perfusion. Data were analysed using a mixed-effects linear regression model. RESULTS: Glucose did not change in CDH limbs relative to AMB in CON (P = .3), EHC (P = .3) or OF (P = .6) groups. There was a decrease in lactate (P < .001) and pyruvate (P < .01) in CDH limbs relative to AMB in all groups. L:P decreased in CON CDH relative to CON AMB (P < .001) but was not different in EHC (P = .6) and OF (P = .07) groups. Urea clearance decreased in CDH limbs relative to AMB in CON (P = .002) and EHC (P < .001), but not in OF (P = .4). MAIN LIMITATIONS: The EHC model may not mimic natural endocrinopathic laminitis. CONCLUSIONS: CDH caused a marked decrease in lamellar glucose metabolism (CON, EHC and OF) and perfusion (CON and EHC) without affecting lamellar glucose concentration. Although cellular energy failure is not a primary pathophysiological event in EHC and OF laminitis models, CDH may act by limiting energy supply to pathologic cellular processes whilst preserving those critical to lamellar homoeostasis.

Evaluation of the effect of laser salpingopharyngostomy on the guttural pouch environment in horses.

BACKGROUND: Laser salpingopharyngostomy has been used as an adjunct to primary medical therapy allowing for topical debridement, topical treatment or to potentially alter the guttural pouch environment in horses with guttural pouch disease. OBJECTIVES: To evaluate the effect of a laser salpingopharyngostomy on the guttural pouch environment in healthy horses. STUDY DESIGN: Experimental study. METHODS: In six adult Standardbred female horses, under standing sedation a stab incision was made ventral to the sternocephalicus tendon and a customised trocar inserted into the medial guttural pouch compartment. Baseline (day 0) temperature, humidity, oxygen (O2 ) and carbon dioxide (CO2 ) levels were recorded. A laser salpingopharyngostomy was subsequently made into the right guttural pouch. The guttural pouch environment was re-sampled as above on days 7 and 14 to detect differences in the local environment of the guttural pouch caused by the laser salpingopharyngostomy. RESULTS: The guttural pouch environment was altered by the laser salpingopharyngostomy. Baseline recorded values within the guttural pouch were highly constant within each horse. Post laser salpingopharyngostomy there was considerable variation within the guttural pouch between horse and during the period of sampling. Specifically, CO2 levels post laser salpingopharyngostomy appeared to be linked directly to the horse's respiratory pattern with peaks and troughs recorded post laser salpingopharyngostomy. The variation in CO2 was significantly different at days 7 and 14 post laser salpingopharyngostomy compared with baseline levels (day 7 = 6 mm Hg, day 14 = 8.83 mm Hg). Oxygen levels were also more varied during sampling compared with baseline (day 7 = 3.4%, day 14 = 1.83%). There was no change in humidity or temperature during the study. MAIN LIMITATIONS: This study was conducted on horses with no evidence of guttural pouch abnormalities or disease. CONCLUSIONS: Laser salpingopharyngostomy alters the guttural pouch environment and this may be useful in the treatment of guttural pouch disease where this alteration is desirable.

Lamellar energy metabolism and perfusion in the euglycaemic hyperinsulinaemic clamp model of equine laminitis.

BACKGROUND: Hyperinsulinaemia is associated with the development of endocrinopathic laminitis; however, the mechanisms remain unclear. OBJECTIVES: Evaluate the effects of hyperinsulinaemia on lamellar energy metabolism and perfusion during laminitis development. STUDY DESIGN: In vivo experiment. METHODS: Eight Standardbred horses were instrumented with a microdialysis probe in the lamellae of a forelimb. A 24 hours baseline period (BASELINE) was followed by 48 hours of a continuous euglycaemic hyperinsulinaemic clamp (EHC) from 24 to 72 hours (CLAMP). Microdialysate was collected every 6 hours and analysed for glucose, lactate and pyruvate concentrations and lactate-to-pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar tissue perfusion. Archived microdialysis samples from six identically instrumented Standardbred horses served as controls (CON). Variables were compared over time and between EHC and CON horses using a mixed-effects linear regression model. RESULTS: Glucose concentration decreased during the CLAMP period in CON and EHC horses (P < .001), but there was no difference between CON and EHC (P > .9). Lactate concentration increased during the CLAMP period in CON and EHC horses (P < .001), however, the rate of increase was significantly higher in EHC horses relative to CON (P = .014). There was a relative increase in pyruvate concentration in EHC horses compared with CON during the CLAMP period (P = .03). L:P increased significantly in CON horses during the CLAMP period (P < .001) but not in EHC (P = .1). Urea clearance did not change in CON (P = .9) or EHC (P = .05) during the CLAMP, but did increase in EHC relative to CON (P = .02). MAIN LIMITATIONS: The effects of microdialysis probe implantation on perfusion and metabolism remain unclear. The EHC model may not mimic natural endocrinopathic laminitis. CONCLUSIONS: Laminitis developed without evidence of lamellar hypoperfusion or energy stress. Therapies to improve perfusion are unlikely to affect the initial development of endocrinopathic laminitis.