Equine laminitis induced with oligofructose

Carbohydrate digestion in the stomach of horses grazed on pasture, fed hay or hay and oats

Concentrations of starch, mono- and disaccharides, fructans, hemicellulose and cellulose were analysed in feed and gastric digesta of horses in relation to acid insoluble ash as a marker indigestible in the stomach. Twenty-four horses were allocated to pasture 24 h/d (PST; n = 4), hay ad libitum (HAY; n = 8), hay ad lib. and oats at 1 g starch/kg body weight (BWT)/meal (OS1; n = 6) and hay ad lib. and oats at 2 g starch/kg BWT/meal (OS2; n = 5). One horse was excluded from the analysis. The horses were fed the ration a minimum of 34 days. Following euthanasia and dissection, digesta was sampled from Pars nonglandularis (PNG) and Pars glandularis (PG). Oat starch concentration in gastric digesta decreased from 309 to 174 g/kg dry matter (DM) in OS1 (44 %-reduction) and from 367 to 261 g/kg DM in OS2 (29 %-reduction) (P < 0.001). Glucose, fructose and sucrose disappeared from gastric digesta distinctly more in PST, HAY and OS1 than in OS2. In PST and HAY, sucrose concentration was completely cleared (P < 0.001). The concentration of fructans was reduced predominantly in PST (84 %-reduction) and HAY (54 %-reduction), mainly in the PNG (P < 0.05). Fructan degradation did not occur in the high-starch diet (OS2). Some evidence for fibre degradation was observed in PST (P < 0.01). Soluble carbohydrates disappear from the stomach dependent on the type of ration, which may lead to changes in the composition of the gastric microbial community and the endogenous response.

Methylated tirilazad may mitigate oligofructose-induced laminitis in horses

Laminitis is a serious health condition that can cause severe pain and lameness in horses. Due to lack of understanding of laminitis, treatments often fail to achieve the desired results. In recent years, we have begun to recognize that laminitis may involve a complex interaction between local and systemic inflammation. Dysbiosis of the gut microbiota has been linked in the development of systemic inflammation, and our previous findings suggest that the development of laminitis is closely linked to the production of harmful metabolites of the gut microbiota. In addition, it was found that localized lesions in the hoof, especially lamellar injuries, are the most direct cause of laminitis. Matrix metalloproteinases have been found to be strongly associated with the development of laminitis. Recent discovery has found that methylated tirilazad has a role in repairing laminar tissue in vitro. However, its efficacy in horses never has been studied. Therefore, we aimed to investigate the efficacy of methylated tirilazad (product name: PTP-102) in the prevention/treatment of oligofructose-induced laminitis. The results showed that oligofructose successfully induced laminitis in horses, resulting in detreated clinical signs. Blood indices (including inflammation-related indices and other related indices) were significantly increased. Observations of dissection and staining showed significant bleeding, swelling, and damage to hoof tissue. Analysis of the gut microbiota showed a significant decrease in abundance and diversity, and a significant increase in the relative abundance of specific bacteria. Following methylated tirilazad intervention, there were a significant improvement in clinical signs, blood markers and lamellar tissue damage. Additionally, methylated tirilazad positively influenced the gut microbiota structure by reducing the relative abundance of genera closely associated with the development of equine laminitis. This suggests that some of the therapeutic mechanism of methylated tirilazad may be linked to its effects on the gut microbiota. Notably, methylated tirilazad had better effect in the treatment group than the prophylactic group, indicating the post-diagnosis utility of methylated tirilazad for laminitis management.

The effect of harvest time of forage on carbohydrate digestion in horses quantified by in vitro and mobile bag techniques

Carbohydrates in forages constitute an important part of the feed ration for all horses. The aim of the present study was to investigate the effect of harvest time on carbohydrate composition and digestion of various grass species. The experiment was divided into three parts 1) characterization of the chemical composition of experimental feeds (6 grass species: meadow fescue [MF], cocksfoot [CF], perennial ryegrass [PR], smooth bromegrass [SB], tall fescue [TF], and timothy [TI], and 3 harvest times: early, medium, and late first cut), 2) measurements of the in vitro digestion of selected experimental feeds (the 6 grass species, and 2 harvest times [early and late]) measured by in vitro gas production, and 3) in vivo digestion of selected experimental feeds (2 grass species: CF and PR, 2 harvest times [early and late]) measured by the mobile bag technique using caecum cannulated horses. An experimental field was established with plots containing each of the grass species in three replicate blocks. Grass samples were cut between 1200 and 1400 h at 4th of June (early first cut), 17th of June (medium first cut), and 1st of July (late first cut) and analyzed for crude protein (CP), neutral detergent fiber with heat stable amylase and free of residual ash (aNDFom) and water-soluble carbohydrates (WSC). The in vitro fermentation was investigated using the ANKOM RF gas production technique, where feeds were incubated for 48 h using horse caecal fluid as an inoculum. Gas production was modeled, and maximum gas production (MGP) was used to evaluate the potential digestibility of the feeds. Based on the chemical analyses and the in vitro experiment, early and late harvested CF and PR were selected for the in vivo experiment, which was conducted as a randomized 4 × 4 Latin square design including four periods, four horses and four feeds. In general, the CP content decreased whereas the aNDFom content increased as the grasses matured. The content of WSC increased in SB and TI, but decreased in CF, and fructans increased in SB, TI, PR, and TF as they matured. The in vitro MGP showed a clearer difference between harvest times than between grass species. Harvest time had larger effect on digestibility than grass species, and a high precaecal disappearance of the WSC fraction was measured by the mobile bag technique. Cocksfoot was identified as a grass species with potentially low digestibility and low WSC content and could potentially be used more for horses.

Oral supplementation with Lithothamnion extract in horses subjected to oligofructose overload intake: effects on systemic inflammation and multiple organ function

Systemic inflammatory response syndrome (SIRS) is a common condition in horses with gastrointestinal disorders. If not prevented or controlled, SIRS promotes multiple organ dysfunctions that may culminate in serious disabilities or even death. The objective of this study was to evaluate the effects of Lithothamnion supplementation on systemic inflammatory response and organ function variables in horses undergoing oligofructose overload (OFO) intake. Twelve healthy horses were randomly divided into control and treated groups. The treated group received Lithothamnion (100 mg/kg bw PO BID) for 7 days before oligofructose intake (10 g/kg PO). Horses underwent clinical and laboratory evaluation immediately before and 6, 12, 18, and 24 h following administration of oligofructose. Parametric data were subjected to ANOVA in randomized blocks, followed by Tukey, and Student's t-tests for mean comparsions. Non-parametric data were analyzed by the Friedman, Dunn's, and Mann-Whitney tests (P < .05). Systemic inflammation and organ dysfunction was evident in both groups; however, these changes were milder and delayed in the treated group. Supplementation attenuated and delayed the tachycardia, tachypnea, leukocytosis, hyperproteinemia, hyperbilirubinemia, hyperalbuminemia and hyperglycemia in treated horses undergoing OFO. Furthermore, increases in packed cell volume, red blood cells, hemoglobin, globulin, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, indirect and direct bilirubin and creatinine were observed only in the control group, remaining unchanged in the treated group. These findings demonstrate the potential of oral supplementation with Lithothamnion to ameliorate systemic inflammation and organ dysfunction in horses at risk of acquiring gastrointestinal disorders.

Presence of Myeloperoxidase in Lamellar Tissue of Horses Induced by an Euglycemic Hyperinsulinemic Clamp

Laminitis is a pathology of the equine digit leading to a failure of the dermo-epidermal interface. Neutrophil activation is recognized as a major factor in SIRS-associated laminitis. Less is known about the role of neutrophil activation in laminitis associated with metabolic disorders. The aim of this descriptive study was to observe whether myeloperoxidase is increased in the laminae during early stage laminitis in three horses subjected to a prolonged euglycemic hyperinsulinemic clamp (pEHC). After 48 h of pEHC-treatment, horses were subjected to euthanasia. Two healthy horses are used as control. Histological sections of lamellar tissue from all horses were immunohistochemically stained for myeloperoxidase and counterstained with hematoxylin-eosin. Histopathological changes that characterize insulin-induced laminitis and increased presence of myeloperoxidase, especially in the dermal lamellae, were increased in histologic sections of pEHC-treated horses. Neutrophil myeloperoxidase release may contribute to the pathophysiology of endocrinopathic laminitis.

Water- and ethanol-soluble carbohydrates of temperate grass pastures: a review of factors affecting concentration and composition

Temperate grasses contain both water- and ethanol-soluble carbohydrates. Water-soluble carbohydrates (WSCs) of temperate grasses include glucose, fructose, sucrose, and fructans (fructose polymers) of varying lengths. Ethanol-soluble carbohydrates (ESCs) consist of glucose, fructose, sucrose, and shorter fructans. WSCs and ESCs have been implicated in equine pasture-associated laminitis and other metabolic disorders. In this paper, the peer-reviewed literature of the past decade was summarized for selected factors influencing concentrations and composition of WSCs and ESCs in temperate grasses. WSC concentrations tended to increase under cool temperatures and during cooler seasons. WSC and ESC concentrations generally increased from morning to evening with a range of -20 to 74 g/kg DM for WSCs. Cultivar choice had variable effects on WSC concentrations. Frequent defoliation usually lowered WSC and fructan concentrations. Nitrogen application increased or decreased WSC concentrations, depending on the amount applied and the grass cultivars. Water stress had variable effects on WSC concentration and composition. Multiple factors should be considered before assuming how certain management or environmental conditions will affect WSCs, ESCs, or individual carbohydrates.

Chemical composition and physical characteristics of faeces in horses with and without free faecal liquid - two case-control studies

Background

Free faecal liquid (FFL) is a condition in horses characterised by two-phase (one solid and one liquid) separation of faeces. Causes of the condition are unknown, but disturbed hindgut fermentation has been suggested as it may alter biochemical composition and appearance of faeces in equines. However, information on faecal composition in horses with FFL is scarce. Faecal chemical composition (dry matter, osmolality, ash, macro minerals, short-chain fatty acids (SCFA) and pH) and physical characteristics (free liquid, sand, water holding capacity and particle size distribution) were compared in horses with (case) and without (control) FFL in two sub-studies. In sub-study I, faeces from 50 case-control horse pairs in Sweden and Norway were sampled in three sampling periods (SP1-SP3). In sub-study II, faeces from 32 case-control horse pairs in Germany were sampled on one occasion.

Results

In sub-study I, faecal concentration and proportion of lactic acid (of total short-chain fatty acids, SCFA) and water holding capacity was lower in case compared to control horses. Other variables (content of dry matter, ash, sodium, calcium, phosphorous, magnesium, sulphur, and concentrations of i-butyric, n-valeric and total SCFA, ammonia-N as proportion of total N, and pH) were similar in faeces from case and control horses. In sub-study II, all analysed variables were similar in faecal samples from case and control horses. Faecal particle size distribution was similar in case and control horses, but the proportion of larger particles (2 and 1 mm) were lower and proportion of smaller particles (< 1 mm) was higher in sub-study I compared to in sub-study II.

Conclusions

To the authors’ knowledge, this is the first study to investigate faecal chemical composition and physical characteristics in horses with FFL. Case and control horses had similar total SCFA, pH and osmolality, indicating that hindgut fermentation was similar. However, small differences in concentration and proportion (of total SCFA) of lactic acid and water holding capacity of faeces were shown and are of interest for further studies of horses with FFL.

Laminitis Updates: Sepsis/Systemic Inflammatory Response Syndrome-Associated Laminitis

Sepsis or systemic inflammatory response syndrome (SIRS) -associated laminitis is a sequela to primary inflammatory conditions (eg, colitis, ischemic intestinal injury, pneumonia, metritis) and results from a dysregulated systemic inflammatory response that ultimately affects the digital lamellae. Local chemokine production, leukocyte migration, and proinflammatory mediator production occur within the lamellae that can lead to catastrophic lamellar failure. Controlling the primary disease, providing supportive care and anti-inflammatory therapy, applying digital cryotherapy, and providing mechanical support are cornerstones to the prevention of sepsis/SIRS-associated laminitis. Novel therapies targeting specific signaling pathways may provide additional therapeutic options in the future.

Synchrotron CT of an equine digit at the Australian Synchrotron Imaging and Medical Beamline

Laminitis is an extremely painful and debilitating condition of horses that can affect their athletic ability and even quality of life. The current gold standard for assessment of laminar tissue is histology, which is the only modality that enables detailed visualization of the lamina. Histology requires dissection of the hoof and therefore can only represent one specific time point. The superior spatial and contrast resolution of synchrotron computed tomography (sCT), when compared with readily available imaging modalities, such as radiographs and conventional CT, provides an opportunity for detailed studies of the lamina without the need for hoof dissection and histological assessment. If the resolution of histology can be matched or even approached, dynamic events, such as laminar blood flow, could also be studied on the microscopic tissue level. To investigate this possible application of sCT further, two objectives are presented: (i) to develop a protocol for sCT of an equine digit using cadaver limbs and (ii) to apply the imaging protocol established during (i) for sCT imaging of the vasculature within the foot using an ex vivo perfusion system to deliver the vascular contrast. The hypotheses were that sCT would allow sufficient resolution for detailed visualization to the level of the secondary lamellae and associated capillaries within the equine digit. Synchrotron CT enabled good visualization of the primary lamellae (average length 3.6 mm) and the ex vivo perfusion system was able to deliver vascular contrast agent to the vessels of the lamina. The individual secondary lamellae (average length 0.142 mm) could not be seen in detail, although differentiation between primary and secondary lamellae was achieved. This approaches, but does not yet reach, the current gold standard, histology, for assessment of the lamellae; however, with further refinement of this imaging technique, improved resolution may be accomplished in future studies.

An Oligosaccharide Rich Diet Increases Akkermansia spp. Bacteria in the Equine Microbiota

Some oligosaccharides induce growth of anti-inflammatory bacterial species and induce regulatory immunity in humans as well as animals. We have shown that the equine gut microbiota and the immune-microbial homeostasis largely stabilize within the first 50 days of life. Furthermore, we have previously established that certain bacterial species in the equine gut correlated with regulatory immunity. Accordingly, we hypothesized that an oligosaccharide rich diet fed to foals during the first 50 days would increase the abundance of bacterial species associated with regulatory immunity, and that this would influence immune responses in the foals. Eight pregnant mares and their foals were fed an oligosaccharide rich diet from 4 weeks before expected parturition until 49 days post-partum. Six mares and foals served as control. Fecal microbiota from mares and foals was characterized using 16S rRNA gene amplicon high throughput sequencing. On Day 49 the test foals had significantly higher abundances of Akkermansia spp. Blood sampled from the foals in the test group on Day 7, 28, and 49 showed non-significant increases in IgA, and decreases in IgG on Day 49. In BALB/cBomTac mice inoculated with gut microbiota from test and control foals we found increased species richness, increased relative abundance of several species identified as potentially anti-inflammatory in horses, which were unclassified Clostridiales, Ruminococcaceae, Ruminococcus, Oscilospira, and Coprococcus. We also found increased il10 expression in the ileum if inoculated with test foal microbiota. We conclude that an oligosaccharide diet fed to foals in the "window of opportunity," the first 50 days of life, increases the abundance of anti-inflammatory species in the microbiota with potentially anti-inflammatory effects on regulatory immunity.

Nutritional Considerations When Dealing with an Obese Adult Equine

Equine obesity is common, reducing quality of life and requiring dietary energy restriction. Equine obesity is identified using subjective body condition scoring. Considerations are given for life stage and health status when managing obese equines. Every effort should be made to maximize feeding duration, and minimize time spent without feed while meeting all essential nutrient requirements. Limiting total daily dry matter intake to 2% of current bodyweight per day of a low caloric, forage-based diet may result in adequate body weight loss. Weight loss and weight management plans should be monitored for success and potential gastrointestinal, metabolic, and/or behavioral complications.

Ethanol-Soluble Carbohydrates of Cool-Season Grasses: Prediction of Concentration by Near-Infrared Reflectance Spectroscopy (NIRS) and Evaluation of Effects of Cultivar and Management

Ethanol-soluble carbohydrates (ESCs) of cool-season grasses include mono- and disaccharides and sometimes short-chain fructans, which may exacerbate the risk of pasture-associated laminitis. A calibration for prediction of ESC concentrations by near-infrared reflectance spectroscopy (NIRS) was developed from 323 samples of four cool-season grass species (orchardgrass, Kentucky bluegrass, tall fescue, and perennial ryegrass) across 10 cultivars collected in central Kentucky in the morning and afternoon over two growing seasons. The calibration, which had accuracy above 95%, was used to predict ESC concentrations of 1,532 samples from the second growing season. ESC concentrations increased in the afternoon compared to the morning across all cultivars. In the majority of samples, ESC concentrations were not affected by nitrogen application to plots. Use of NIRS has the potential to evaluate management and cultivar effects on ESC concentrations in cool-season grass pastures.

The application of a new laminitis scoring method to model the rate and pattern of improvement from equine endocrinopathic laminitis in a clinical setting

Background

Endocrinopathic, or hyperinsulinaemia-associated laminitis (HAL) is a common and debilitating equine foot disease, and although no pharmacological treatments are registered, several are under development. To evaluate the effect of such treatments, an accurate and consistent method is needed to track the clinical signs of laminitis over time, and the natural history of the disease, in terms of a ‘normal’ pattern of improvement, needs to be understood. This study examined the improvement pattern in clinical cases of naturally-occurring HAL subjected to a range of best-practice interventions, using two different scoring methods. Eighty horses and ponies with suspected HAL were enrolled in a study conducted at 16 veterinary practices across Germany. The severity of laminitis was assessed by independent veterinarians using both the traditional Obel method and a modified Obel method developed by Meier and colleagues. Assessments were made on the day of diagnosis (d 0), then on days 4, 9, 14, 25 and 42 during the intervention period. Pain medications were withheld for 24 h prior to clinical examination in all cases.

Results

Time to marked improvement from laminitis varied between individuals, but was difficult to monitor accurately using the Obel method, with the median grade being 2/4 on days 0 and 4, then 0/4 from d 9 onwards. More subtle changes could be identified using the Meier method, however, and the median scores were seen to follow the form of an exponential decay model in most horses, improving from 8/12 on d 0, to 0/12 on d 25. Within this composite scoring method, considerable variation was observed in the rate of improvement of individual clinical signs, with the average time taken for each sign to reach a median score of 0 ranging from 4 days (foot lift and weight shifting) to 25 days (gait when turned in a circle) across all 80 horses.

Conclusions

The Meier method provides a reliable and consistent method for monitoring the clinical status of horses with HAL, and despite the variability, the pattern of improvement described here should provide a useful benchmark against which individual cases and new treatments can be assessed.

Changes of microbial and metabolome of the equine hindgut during oligofructose-induced laminitis

Background

Laminitis is a common and serve disease which caused by inflammation and pathological changes of the laminar junction. However, the pathologic mechanism remains unclear. In this study we aimed to investigate changes of the gut microbiota and metabolomics in oligofructose-induced laminitis of horses.

Results

Animals submitted to treatment with oligofructose had lower fecal pH but higher lactic acid, histamine, and Lipopolysaccharide (LPS) in serum. Meanwhile, oligofructose altered composition of the hindgut bacterial community, demonstrated by increasing relative abundance of Lactobacillus and Megasphaera. In addition, the metabolome analysis revealed that treatment with oligofructose decreased 84 metabolites while 53 metabolites increased, such as dihydrothymine, N3,N4-Dimethyl-L-arginine, 10E,12Z-Octadecadienoic acid, and asparagine. Pathway analysis revealed that aldosterone synthesis and secretion, regulation of lipolysis in adipocytes, steroid hormone biosynthesis, pyrimidine metabolism, biosynthesis of unsaturated fatty acids, and galactose metabolism were significantly different between healthy and laminitis horses. Furthermore, correlation analysis between gut microbiota and metabolites indicated that Lactobacillus and/or Megasphaera were positively associated with the dihydrothymine, N3,N4-Dimethyl-L-arginine, 10E,12Z-Octadecadienoic acid, and asparagine.

Conclusions

These results revealed that disturbance of gut microbiota and changes of metabolites were occurred during the development of equine laminitis, and these results may provide novel insights to detect biomarkers for a better understanding of the potential mechanism and prevention strategies for laminitis in horses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-020-02686-9.

Genetics and Signaling Pathways of Laminitis

Laminitis is a devastating disease with diverse etiologies and few, if any, effective treatments. Gene expression and hypothesis-generating genomic studies have provided a fresh look at the key molecular players at crucial timepoints in diverse experimental and naturally affected tissues. We summarize findings to date, and propose a unifying model of the laminitis disease process that includes several pathogenesis concepts shared with other diseases of epidermal and epithelial tissues. The value of these new pathways as potential therapeutic targets is exciting but will require careful future work to validate new methods and launch systematic clinical trials.

The influence of equine body weight gain on inflammatory cytokine expressions of adipose tissue in response to endotoxin challenge

Background

Human obesity is linked with systemic inflammation. However, it is still controversial if equines produce more inflammatory cytokines with increasing body weight and if the production of those show breed type specific patterns. The main objective of this study was to determine if diet induced obesity is associated with increased inflammatory signatures in adipose tissue of equines and if a breed predisposition exists between ponies and horses. Additionally, we aimed to identify adipose tissue depot differences in inflammatory cytokine expression. Nineteen healthy, non-overweight and metabolically healthy equines received a hypercaloric diet for 2 years. Body weight, body condition score and cresty neck score were assessed weekly throughout the study. At three time points, insulin sensitivity was determined by a combined glucose-insulin test. Adipose tissue samples were collected from two intra-abdominal and two subcutaneous depots under general anesthesia at each time point after an endotoxin trigger. In the adipose tissue samples levels of CD68 mRNA (a marker of macrophage infiltration) and pro-inflammatory cytokine mRNA (IL-1β, IL-6 and TNFα) were analyzed with RT-qPCR. As markers of lipid metabolism mRNA levels of lipoprotein lipase (LPL) and fatty acid binding protein 4 (FABP4) were determined with RT-qPCR.

Results

CD68 mRNA levels increased with body weight gain in several adipose tissue (AT) depots (Wilcoxon signed rank test with Bonferroni correction; retroperitoneal AT horses: P = 0.023, mesocolonial AT horses: P = 0.023, subcutaneous tail head AT ponies: P = 0.015). In both abdominal depots CD68 mRNA levels were higher than in subcutaneous adipose tissue depots (Kruskal–Wallis-ANOVA with Bonferroni correction: P < 0.05). No breed related differences were found. Pro-inflammatory cytokine mRNA IL-1β, IL-6 and TNFα levels were higher in subcutaneous depots compared to abdominal depots after body weight gain. IL-1β, IL-6 and TNFα mRNA levels of mesocolon adipose tissue were higher in obese horses compared to obese ponies (Mann–Whitney-U test; IL-1β: P = 0.006; IL-6: P = 0.003; TNFα: P = 0.049). In general, horses had higher FABP4 and LPL mRNA levels compared to ponies in neck AT and tail AT at all time points.

Conclusion

Our findings suggest an increased invasion of macrophages in intra-abdominal adipose tissue with increasing body weight gain in equines in combination with a low dose endotoxin stimulus. This might predispose equines to obesity related comorbidities. In obese horses mesocolon adipose tissue showed higher inflammatory cytokine expression compared to obese ponies. Additionally, subcutaneous adipose tissue expressed more pro-inflammatory cytokines compared to intra-abdominal adipose tissue. Horses had higher FABP4 and LPL mRNA levels in selected AT depots which may indicate a higher fat storage capacity than in ponies. The differences in lipid storage might be associated with a higher susceptibility to obesity-related comorbidities in ponies in comparison to 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.

Novel technique for prevention of rotation of the distal phalanx relative to the hoof wall in horses with acute laminitis

OBJECTIVE

To determine the holding capacity of a 5.5-mm-diameter cortical bone screw when placed in the third phalanx (P3) of horses and assess whether screw placement through the dorsal hoof wall into P3 would be tolerated by clinically normal horses and would alleviate signs of pain and prevent P3 rotation in horses with oligofructose-induced laminitis.

ANIMALS

40 limbs from 10 equine cadavers and 19 clinically normal adult horses.

PROCEDURES

In part 1 of a 3-part study, a 5.5-mm-diameter cortical bone screw was inserted by use of a lag-screw technique through the dorsal hoof wall midline into P3 of 40 cadaveric limbs and tested to failure to determine screw pullout force. In part 2, 6 horses had 5.5-mm-diameter cortical bone screws placed in both forefeet as described for part 1. Screws were removed 4 days after placement. Horses were monitored for lameness before and for 2 weeks after screw removal. In part 3, 13 horses were randomly assigned to serve as controls (n = 3) or undergo screw placement without (group 2; 6) or with (group 3; 4) a washer. Following the acquisition of baseline data, horses were sedated and administered oligofructose (10 g/kg) via a stomach tube. Twenty-four hours later, screws were placed as previously described in both forefeet of horses in groups 2 and 3. Horses were assessed every 4 hours, and radiographic images of the feet were obtained at 96 and 120 hours after oligofructose administration. Horses were euthanized, and the feet were harvested for histologic examination.

RESULTS

The mean ± SD screw pullout force was 3,908.7 ± 1,473.4 N, and it was positively affected by the depth of screw insertion into P3. Horses of part 2 tolerated screw placement and removal well and did not become lame. All horses of part 3 developed signs of acute lameness, and the distance between P3 and the dorsal hoof wall increased slightly over time. The change in the ratio of the dorsal hoof wall width at the extensor process of P3 to that at the tip of P3 over time was the only variable significantly associated with treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Placement of a 5.5-mm-diameter cortical bone screw through the dorsal hoof wall into P3 had sufficient holding power to counteract the pull of the deep digital flexor tendon in approximately 500-kg horses, and placement of such a screw was well tolerated by clinically normal horses but did not alleviate signs of pain in horses with oligofructose-induced laminitis. Further research is necessary before this technique can be recommended for horses with naturally occurring acute laminitis.

The Equine Hoof: Laminitis, Progenitor (Stem) Cells, and Therapy Development

The equine hoof capsule, composed of modified epidermis and dermis, is vital for protecting the third phalanx from forces of locomotion. There are descriptions of laminitis, defined as inflammation of sensitive hoof tissues but recognized as pathologic changes with or without inflammatory mediators, in the earliest records of domesticated horses. Laminitis can range from mild to serious, and signs can be acute, chronic, or transition from acute, severe inflammation to permanently abnormal tissue. Damage within the intricate dermal and epidermal connections of the primary and secondary lamellae is often associated with lifelong changes in hoof growth, repair, and conformation. Decades of research contribute to contemporary standards of care that include systemic and local therapies as well as mechanical hoof support. Despite this, consistent mechanisms to restore healthy tissue formation following a laminitic insult are lacking. Endogenous and exogenous progenitor cell contributions to healthy tissue formation is established for most tissues. There is comparably little information about equine hoof progenitor cells. Equine hoof anatomy, laminitis, and progenitor cells are covered in this review. The potential of progenitor cells to advance in vitro equine hoof tissue models and translate to clinical therapies may significantly improve prevention and treatment of a devastating condition that has afflicted equine companions throughout history.

Influence of digital hypothermia on lamellar events related to IL-6/gp130 signalling in equine sepsis-related laminitis

BACKGROUND

Interleukin-6 (IL-6) is consistently increased in the digital lamellae in different studies of sepsis-related laminitis (SRL). IL-6 signalling through the gp130 receptor activates similar signalling (i.e. mTORC1-related signalling) previously reported to be activated in models of endocrinopathic laminitis.

OBJECTIVES

To assess the activation state of signalling proteins downstream of IL-6/gp130 receptor complex activation in an experimental model of SRL.

STUDY DESIGN

Randomised experimental study.

METHODS

Lamellar phospho-(P) protein concentrations downstream of the IL-6/gp130 receptors were assessed in the oligofructose (OF) model of SRL. Fifteen Standardbred horses were administered water (CON, n = 8) or oligofructose (OF, n = 7) via a nasogastric tube. At 12 h post-OF/water administration, one randomly assigned forelimb was exposed to continuous digital hypothermia (CDH) by placement in ice water (ICE, maintained at <7°C); the other forelimb was maintained at ambient temperature (AMB). Lamellar tissue samples were collected after 24 h of CDH from both ICE and AMB forelimbs and immediately snap-frozen. Lamellar proteins of interest were assessed by immunoblotting and immunofluorescence.

RESULTS

Immunoblotting revealed increase (P<0.05) in the phosphorylation states of Akt (Ser 473), RPS6 (Ser235/236), RPS6 (Ser240/244), STAT3 (Ser727) and STAT3 (Tyr705) in lamellar tissue from OF-treated animals (AMB OF vs. AMB CON limbs); CDH resulted in decreased (P<0.05) lamellar concentrations of phosphorylated Akt, p70S6K, RPS6 (235/236), RPS6 (240/244) and STAT3 (S727) in OF-treated animals (AMB OF vs. ICE OF). Immunofluorescence showed that activated/phosphorylated forms of RPS6 and STAT3 were primarily localised to lamellar epithelial cells.

MAIN LIMITATIONS

The nature, sequence and timing of sub-cellular events in this experimental model may differ from those that accompany naturally occurring sepsis.

CONCLUSIONS

There were increased lamellar concentrations of activated signalling proteins downstream of the IL-6/Gp130 receptor complex in OF-treated horses; CDH inhibited this activation for the majority of the proteins assessed. These results demonstrate similar lamellar signalling (e.g. mTORC1-related signalling) and, therefore, possible therapeutic targets occurring in sepsis-related laminitis as previously reported in models of endocrinopathic laminitis.

Modification of the equine gastrointestinal microbiota by Jerusalem artichoke meal supplementation

The objective of this study was to investigate the impact of natural prebiotic active compounds on the microbial composition in different regions of the equine gastrointestinal tract. Twelve adult horses (body weight [bwt] 534 ± 64.5 kg; age 14 ± 7.5 years) were randomly divided into two feeding groups. Six horses received a basal diet consisting of 1.5 kg hay/100 kg bwt x d^-1 and oat grains equal to 1.19 g starch/kg bwt x d^-1, supplemented with Jerusalem artichoke meal providing prebiotic fructooligosaccharides + inulin in a quantity of 0.15 g/kg bwt x d^-1. The remaining horses received a placebo added to the basal diet. The horses were fed for 21 d and euthanized at the end of the feeding period. Digesta samples from different parts of the gastrointestinal tract were taken, DNA extracted and the V1-V2 region of the 16S rRNA gene amplified. Supplementation with the prebiotic increased the relative abundance of Lactobacillus (P < 0.05), with a concurrent reduction of the relative abundance of Streptococcus mainly in the stomach (P < 0.05). In the hindgut, the supplemental prebiotic also increased the relative abundance of Lactobacillus but further reduced the relative abundance of fibrolytic bacteria, specifically the unclassified members of the families Lachnospiraceae (P < 0.05) and Ruminococcaceae. The relative abundance of the genus Ruminococcus increased solely in the caecum and colon transversum. Overall, the addition of the prebiotic significantly increased the diversity in nearly all parts of the gastrointestinal tract (P < 0.05). The feeding of this natural prebiotic compound to horses had an impact on the microbial community in the entire gastrointestinal tract. Furthermore, the effect on the bacterial community in the foregut (especially the stomach) was more pronounced in comparison to the effect in the hindgut. Therefore, the impact on stomach health should be carefully considered.

A "modified Obel" method for the severity scoring of (endocrinopathic) equine laminitis

BACKGROUND

Laminitis is a common equine disease characterized by foot pain, and is commonly diagnosed using a five-grade Obel system developed in 1948 using sepsis-related cases. However, endocrinopathic laminitis is now the most common form of the disease and clinical signs may be mild, or spread across two Obel grades. This paper describes a modified method which assigns scores to discreet clinical signs, providing a wider scale suitable for use in a research setting.

METHODS

The "modified Obel" method was developed using an iterative process. First, a prototype method was developed during the detailed observation of 37 ponies undergoing a laminitis induction experiment. The final method was refined and validated using video footage taken during the induction study and from a clinical trial of naturally occurring endocrinopathic laminitis cases. The Obel method was deconstructed and key laminitis signs were evaluated to develop a three-stage, five criteria method that employs a severity scale of 0-12. Veterinarians (n = 28) were recruited to watch and assess 15 video recordings of cases of varying severity, using the Obel and "modified Obel" methods. The inter-observer agreement (reproducibility) was determined using Kendall's coefficient of concordance (Kendall W) and Krippendorf's alpha reliability coefficient. A total of 14 veterinarians repeated the exercise 2-4 weeks after their original assessment, to determine intra-observer agreement (repeatability), assessed using a weighted kappa statistic (kw). Agreement between methods was calculated by converting all "modified Obel" scores to Obel grades and calculating the mean and distribution of the differences.

RESULTS

The "modified Obel" and Obel methods showed excellent and similar inter-observer agreement based on the Kendall W value (0.87, P < 0.001 vs. 0.85, P < 0.001) and Krippendorf's alpha (95% CI) value (0.83 [0.53-0.90] vs. 0.77 [0.55-0.85]). Based on the kw value, the "modified Obel" method also had substantial repeatability, although slightly less than the Obel method, (0.80 vs. 0.91). Excellent agreement between the methods was found, with the mean difference (95% CI), comparing the Obel grade, with the "modified Obel" score converted to an Obel grade, being -0.12 (-0.19 to -0.06) grades. The Obel and converted "modified Obel" grades were identical 62% of the time (259/420) and a difference of one grade (higher or lower) occurred in 35% of cases (148/420).

CONCLUSION

Both methods show excellent agreement, reproducibility and repeatability when used to diagnose endocrinopathic laminitis. The "modified Obel" method is a three-step examination process for severity-scoring of endocrinopathic laminitis, initially proposed for use within a research setting. When using the modified method a diagnosis of laminitis also requires clinical acumen. The allocation of scores for specific clinical signs should be particularly useful in research trials monitoring laminitis recovery.

Are There Shared Mechanisms in the Pathophysiology of Different Clinical Forms of Laminitis and What Are the Implications for Prevention and Treatment?

Laminitis is a consequence of primary disease processes elsewhere in the body. The key pathophysiologic events are insulin dysregulation in endocrinopathic laminitis, ischemia in supporting limb laminitis, and inflammation in sepsis-related laminitis. These apparently disparate mechanisms converge to cause lamellar attachment failure through epithelial cell adhesion loss and stretch, possibly mediated by common growth factor signaling pathways. Tissue damage through mechanical distraction, inflammation, pain, and a proliferative epithelial healing response are features of acute laminitis regardless of the cause. Preventive and treatment strategies based on knowledge of these unique and common mechanistic events are likely to improve clinical outcomes.

Continuous digital hypothermia prevents lamellar failure in the euglycaemic hyperinsulinaemic clamp model of equine laminitis

BACKGROUND

Continuous digital hypothermia can prevent the development and progression of laminitis associated with sepsis but its effects on laminitis due to hyperinsulinaemia are unknown.

OBJECTIVES

To determine the effects of continuous digital hypothermia on laminitis development in the euglycaemic hyperinsulinaemic clamp model.

STUDY DESIGN

Randomised, controlled (within subject), blinded, experiment.

METHODS

Eight clinically normal Standardbred horses underwent laminitis induction using the euglycaemic hyperinsulinaemic clamp model (EHC). At initiation of the EHC, one forelimb was continuously cooled (ICE), with the other maintained at ambient temperature (AMB). Dorsal lamellar sections (proximal, middle, distal) were harvested 48 h after initiation of the EHC and were analysed using histological scoring (0-3) and histomorphometry. Cellular proliferation was quantified by counting epidermal cell nuclei staining positive with an immunohistochemical proliferation marker (TPX2).

RESULTS

Severe elongation and disruption of SEL with dermo-epidermal separation (score of 3) was observed in all AMB feet at one or more section locations, but was not observed in any ICE sections. Overall 92% of the AMB sections received the most severe histological score (grade 3) and 8% were grade 2, whereas ICE sections were classified as either grade 1 (50%) or grade 2 (50%). Relative to AMB feet, ICE sections were 98% less likely to exhibit grades 2 or 3 (OR: 0.02, 95% CI 0.001, 0.365; P<0.01). Histomorphometry measurements of total and nonkeratinised primary epidermal lamellar length were significantly increased (P<0.01) in AMB limbs compared with ICE. TPX2 positive cell counts were significantly increased (P<0.01) in AMB limbs compared with ICE.

MAIN LIMITATIONS

Continuous digital hypothermia was initiated before recognition of laminitis and therefore the clinical applicability requires further investigation.

CONCLUSIONS

Continuous digital hypothermia reduced the severity of laminitis in the EHC model and prevented histological lesions compatible with lamellar structural failure.

Whole body and partial body cryotherapies - lessons from human practice and possible application for horses

Whole body and partial body cryotherapies (WBC and PBC) have been successfully used in human medicine, and currently also are being proposed in veterinary practice.

In horses, only the partial body cryotherapy provided in cryosauna is considered, due to the technical conditions. These therapies have been dedicated to human patients with rheumatic and inflammatory diseases as well as an assistance during training in athletes. The anti-inflammatory effects have been demonstrated clinically and indicated by the changes in several hematological and immunological parameters, however, various patterns have been described, depending on the protocols and the treating subjects. The numbers of white blood cells and the differential counts either increased or remained unchanged but the cytokine concentrations generally changed towards various anti-inflammatory profiles and the modifications of immunological molecules having paracrine effects have been reported.

In equine practice, local cold therapies have been successfully used, so the therapy in cryosauna, which allows for a much shorter procedure with much lower temperature seems promising.

Evaluation of digital cryotherapy using a commercially available sleeve style ice boot in healthy horses and horses receiving i.v. endotoxin

BACKGROUND

Continuous digital cryotherapy experimentally prevents development and reduces severity of sepsis-associated laminitis. A sleeve style ice boot where ice is in direct contact with the skin, and water drains from the boot is being used clinically for distal limb cryotherapy. The degree of cooling achieved by this boot is unknown.

OBJECTIVES

Evaluate skin and lamellar cooling after application of the ice sleeve in healthy horses, and the same horses during an endotoxaemia model.

STUDY DESIGN

Prospective study, crossover design.

METHODS

In eight healthy horses thermocouples were inserted into dorsal lamellae of both front feet, and under skin on both metacarpi. One forelimb received cryotherapy using sleeve style ice boot, with contralateral limb as control. Temperature was recorded on data logging devices at 5 min intervals during each cryotherapy session. Day 1: temperature data was collected for healthy horses. Day 2: data was collected for the same horses during i.v. administration of endotoxin.

RESULTS

In healthy and endotoxaemic horses, the sleeve style ice boot significantly decreased mean skin (7.2°C and 5.8°C respectively) and lamellar (10.8°C and 9.6°C respectively) temperatures compared with control limbs (P<0.001). Skin and lamellar temperatures in endotoxaemic horses undergoing cryotherapy were significantly colder than in healthy horses (P = 0.01).

MAIN LIMITATIONS

Order of treatment not randomised.

CONCLUSIONS

The boot caused significant decreases in lamellar temperatures compared with untreated control limbs in all horses. Endotoxaemic horses had significantly colder lamellae and skin than healthy horses. This study is the first to show that a sleeve style boot, where ice does not cover the hoof, can cause significant decreases in lamellar temperatures through cooling of blood as it travels to the foot.

Browse silage as potential feed for captive wild ungulates in southern Africa: A review

The objective of the review was to assess the potential of indigenous browse trees as sustainable feed supplement in the form of silage for captive wild ungulates. Several attempts to use silage as feed in zoos in temperate regions have been conducted with success. Information on silage from the indigenous browse trees preferred by wild ungulates in southern Africa is scanty. The use of silage from the browse trees is of interest as it has potential to reduce or replace expensive feed sources (pellets, fruits and farm produce) currently offered in southern African zoos, game farms and reserves, especially during the cold-dry season. Considerable leaf biomass from the indigenous browse trees can be produced for silage making. High nutrient content and minerals from indigenous browsable trees are highly recognised. Indigenous browse trees have low water-soluble carbohydrates (WSC) that render them undesirable for fermentation. Techniques such as wilting browse leaves, mixing cereal crops with browse leaves, and use of additives such as urea and enzymes have been studied extensively to increase WSC of silage from the indigenous browse trees. Anti-nutritional factors from the indigenous browse preferred by the wild ungulates have also been studied extensively. Indigenous browse silages are a potential feed resource for the captive wild ungulates. If the browse trees are used to make silage, they are likely to improve performance of wild ungulates in captivity, especially during the cold-dry season when browse is scarce. Research is needed to assess the feasibility of sustainable production and the effective use of silage from indigenous browse trees in southern Africa. Improving intake and nutrient utilisation and reducing the concentrations of anti-nutritional compounds in silage from the indigenous browse trees of southern Africa should be the focus for animal nutrition research that need further investigation.

Effect of Continuous Digital Hypothermia on Lamellar Inflammatory Signaling When Applied at a Clinically-Relevant Timepoint in the Oligofructose Laminitis Model

BACKGROUND

Although continuous digital hypothermia (CDH) protects lamellae from injury in the oligofructose (OF) model of sepsis-related laminitis (SRL), conflicting results exist from these studies regarding effects of CDH on lamellar inflammatory events.

HYPOTHESIS/OBJECTIVES

To determine the effect of CDH on lamellar inflammatory events in normal and OF-treated horses when instituted at a clinically relevant time point (onset of clinical signs of sepsis in this model).

ANIMALS

Standardbred geldings (n = 15) aged 3-11 years were used.

METHODS

In a randomized, controlled discovery study, animals were administered either OF (OF group, n = 8) or water (CON group, n = 8) by nasogastric tube and CDH was initiated in one forelimb (ICE) 12 hours later. Lamellar tissue samples were collected 24 hours after initiation of CDH (ICE and ambient [AMB] forelimbs). Lamellar mRNA concentrations of inflammatory mediators and lamellar leukocyte numbers were assessed using qPCR and immunohistochemistry, respectively; values from four sample groups (CON AMB, OF AMB, CON ICE, and OF ICE) were analyzed using mixed model linear regression.

RESULTS

Although lamellar mRNA concentrations of multiple inflammatory mediators (IL-1β, IL-6, CXCL1, MCP2, COX-2) were increased after OF administration (OF AMB group versus CON AMB; P < 0.05), only 2 inflammatory mediators (IL-6 and COX-2) and lamellar leukocyte numbers were decreased with CDH (OF ICE versus OF AMB; P < 0.05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Continuous digital hypothermia initiated at a time point similar to that commonly used clinically (clinical onset of sepsis) resulted in a more focused inhibition of inflammatory signaling.

Intraruminal infusion of oligofructose alters ruminal microbiota and induces acute laminitis in sheep

The objectives of this study were to examine the clinical response, changes in ruminal bacterial microbiota, and inflammatory response in lamellar tissues during oligofructose-induced laminitis. Ten fistulated sheep were randomly assigned into a control group ( = 5) and a treatment group ( = 5). The treatment group was infused with oligofructose (21 g/kg BW) by rumen cannula, and the control group was sham-treated with saline. Results showed that all 5 sheep treated with oligofructose developed anorexia and diarrhea 8 to 12 h after the administration of oligofructose. By 12 to 24 h after treatment, the treatment group developed lameness and roach back. Compared with the control group, oligofructose administration decreased ( < 0.001) the rumen pH and concentrations of total VFA and increased ( < 0.001) the level of lactic acid in the rumen. Microbial data analysis revealed that oligofructose infusion increased the abundance of ( = 0.009) and ( = 0.008) and decreased the percentage of unclassified Christensenellaceae ( = 0.028), unclassified Ruminococcaceae ( = 0.009), ( = 0.016), unclassified Lachnospiraceae ( = 0.009), and ( = 0.009) compared with the control group. Oligofructose infusion decreased the ACE ( = 0.047) and Shannon ( = 0.009) indices compared with the control group. The histomorphology analysis revealed that oligofructose overload resulted in damage to the dermoepidermal junction in the lamellar tissue of sheep. Quantitative real-time PCR results showed that compared with the control group, the mRNA expression of membrane-type metalloproteinase-1 ( = 0.049) was downregulated whereas the expression of proinflammatory IL-6 ( = 0.004) and matrix metalloprotease-9 ( = 0.037) was upregulated in the lamellar tissues of the oligofructose treatment group. In general, the present study provides the foundation for a sheep model of oligofructose-overload-induced acute laminitis that could be used in later experiments. Our findings suggest that intraruminal infusion of oligofructose altered ruminal microbiota and resulted in acute laminitis and that the inflammatory damage to the lamellae tissue may be related to the upregulation of matrix metalloprotease-9. The information generated will provide more insight into the systemic effects of lameness caused by oligofructose overload in sheep.

The effect of hypothermia on influx of leukocytes in the digital lamellae of horses with oligofructose-induced laminitis

Sepsis-related laminitis (SRL) is a common complication in the septic/endotoxemic critically-ill equine patient, in which lamellar injury and failure commonly lead to crippling distal displacement of the distal phalanx. Similar to organ injury in human sepsis, lamellar injury in SRL has been associated with inflammatory events, including the influx of leukocytes into the lamellar tissue and markedly increased expression of a wide array of inflammatory mediators at the onset of Obel grade 1 (OG1) laminitis. The only treatment reported both clinically and experimentally to protect the lamellae in SRL, local hypothermia ("cryotherapy"), has been demonstrated to effectively inhibit lamellar expression of multiple inflammatory mediators when initiated at the time of administration of a carbohydrate overload in experimental models of SRL. However, the effect of hypothermia on leukocyte influx into affected tissue has not been assessed. We hypothesized that cryotherapy inhibits leukocyte emigration into the digital lamellae in SRL. Immunohistochemical staining using leukocyte markers MAC387 (marker of neutrophils, activated monocytes) and CD163 (monocyte/macrophage-specific marker) was performed on archived lamellar tissue samples from an experimental model of SRL in which one forelimb was maintained at ambient temperature (AMB) and one forelimb was immersed in ice water (ICE) immediately following enteral oligofructose administration (10g/kg, n=14 horses). Lamellae were harvested at 24h post-oligofructose administration (DEV, n=7) or at the onset of OG1 laminitis (OG1, n=7). Both MAC387-positive and CD163-positive cells were counted by a single blinded investigator on images [n=10 (40× fields/digit for MAC387 and 20x fields/digit for CD163)] obtained using Aperio microscopy imaging analysis software. Data were assessed for normality and analyzed with a paired t-test and one-way ANOVA with significance set at p<0.05. MAC387-positive cells were present in low numbers in the lamellar tissue and were decreased in the hypothermic limbs (vs. AMB limbs, p<0.05) in the OG1 group; no change in CD163-positive cell numbers was noted across the conditions of the model. This study demonstrated that hypothermia of the distal limbs instituted early in the disease process in the horse at risk of SRL significantly attenuates the increase of MAC387-positive leukocytes in the digital lamellae, but has minimal effect on increases in lamellar concentrations of the major leukocyte cell type present in that tissue, CD163-positive mononuclear cells.

A liquid chromatography-tandem mass spectrometry-based investigation of the lamellar interstitial metabolome in healthy horses and during experimental laminitis induction

Lamellar bioenergetic failure is thought to contribute to laminitis pathogenesis but current knowledge of lamellar bioenergetic physiology is limited. Metabolomic analysis (MA) can systematically profile multiple metabolites. Applied to lamellar microdialysis samples (dialysate), lamellar bioenergetic changes during laminitis (the laminitis metabolome) can be characterised. The objectives of this study were to develop a technique for targeted MA of lamellar and skin dialysates in normal horses, and to compare the lamellar and plasma metabolomic profiles of normal horses with those from horses developing experimentally induced laminitis. Archived lamellar and skin dialysates (n = 7) and tissues (n = 6) from normal horses, and lamellar dialysate and plasma from horses given either 10 g/kg oligofructose (treatment group, OFT; n = 4) or sham (control group, CON; n = 4) were analysed. The concentrations of 44 intermediates of central carbon metabolism (CCM) were determined using liquid chromatography-tandem mass spectrometry. Data were analysed using multivariate (MVA) and univariate (UVA) analysis methods. The plasma metabolome appeared to be more variable than the lamellar metabolome by MVA, driven by malate, pyruvate, aconitate and glycolate. In lamellar dialysate, these metabolites decreased in OFT horses at the later time points. Plasma malate was markedly increased after 6 h in OFT horses. Plasma malate concentrations between OFT and CON at this time point were significantly different by UVA. MA of lamellar CCM was capable of differentiating horses developing experimental laminitis from controls. Lamellar malate, pyruvate, aconitate and glycolate, and plasma malate alone were identified as the source of differentiation between OFT and CON groups. These results highlighted clear discriminators between OFT and CON horses, suggesting that changes in energy metabolism occur locally in the lamellar tissue during laminitis development. The biological significance of these alterations requires further investigation.

Distribution of technetium-99m PEG-liposomes during oligofructose-induced laminitis development in horses

Liposomes are phospholipid nanoparticles used for targeted drug delivery. This study aimed to determine whether intravenous liposomes accumulate in lamellar tissue during laminitis development in horses so as to assess their potential for targeted lamellar drug delivery. Polyethylene-glycol (PEG) coated liposomes were prepared according to the film hydration method and labelled using (99m)Tc-hexamethyl-propylene-amine-oxime. Six horses received 10 g/kg oligofructose via nasogastric tube to induce laminitis, and four control horses received water via nasogastric tube. All horses received 300 µmol (99m)Tc-PEG-liposomes (5.5 GBq) plus 5.5 µmol/kg PEG-liposomes by slow intravenous infusion. Scintigraphic imaging was performed at 0, 6 and 12 h post-infusion. Technetium-99m liposome uptake was measured in regions of interest over the hoof, fetlock and metacarpus. At the study end-point horses were euthanased, tissue samples collected and tissue liposome levels were calculated as the percentage of the injected dose of (99m)Tc-liposomes per kilogram of tissue. Data were analysed non-parametrically. All horses receiving oligofructose developed clinical and histological signs of laminitis. Technetium-99m liposome uptake in the hoof increased with time in laminitis horses (P = 0.04), but decreased with time in control horses (P = 0.01). Technetium-99m liposome levels in lamellar tissue from laminitis horses were 3.2-fold higher than controls (P = 0.02) and were also higher in laminitis vs. control skin, muscle, jejunum, colon, and kidney (P < 0.05). Liposomes accumulated in lamellar tissue during oligofructose-induced laminitis development and demonstrated potential for targeted lamellar drug delivery in acute laminitis. This study provides further evidence that lamellar inflammation occurs during laminitis development. Liposome accumulation also occurred in the skin, muscle, jejunum, colon and kidneys, suggesting systemic inflammation in this model.

Pathology of Natural Cases of Equine Endocrinopathic Laminitis Associated With Hyperinsulinemia

Laminitis in equids is a clinical syndrome usually associated with systemic disease. Endocrinopathies recently have been recognized as the most common cause of laminitis, with hyperinsulinemia playing a key role. Descriptions of laminitis-associated lesions have been confusing due to the wide range of experimental models used, failure of adequate clinical documentation for naturally occurring cases, lack of separate analysis of inflammatory and endocrinopathic laminitis, and uncertainty regarding normal morphological variation of lamellae. In this study, lamellar morphology and pathology were described in 14 laminitic horses and ponies that had hyperinsulinemia (>20 mIU/l), with reference to 25 age- and breed-matched controls. The type and severity of lesions noted had no correlation with reported clinical duration and in at least some cases must have preceded it. Lesions were largely localized abaxially within the lamellar tissue and included apoptotic cell death, as well as lamellar fusion, hyperplasia, and partial replacement with aberrant keratin containing nucleated debris and proteinaceous lakes. The lesions resulted in irregular margins between the inner horn and the lamellar tissue. Acute separation originated from the abaxial region, with minimal associated inflammation. Axially, epidermal lamellar tapering was the most frequent morphological observation. The lesions in these chronic cases of laminitis were similar to those described in some inflammatory laminitis models and contained features seen in developmental phases of hyperinsulinemic models. These findings support the theory that repeated episodes of subclinical laminitis occur prior to clinical presentation. In addition, the pathology does not include extensive basement membrane failure seen in some inflammatory models.

Ultrafiltration of equine digital lamellar tissue

There are no experimentally validated pharmacological means of preventing laminitis; however, locally acting pharmaceutical agents with the potential to prevent laminitis have been identified. Demonstrating therapeutic drug concentrations in lamellar tissue is essential for evaluating the efficacy of these agents. The aim of this study was to develop an experimental technique for repeatedly sampling lamellar interstitial fluid. A technique for placing ultrafiltration probes was developed in vitro using 15 cadaver limbs. Subsequently, lamellar ultrafiltration probes were placed in one forelimb in six living horses. Interstitial fluid was collected continuously from the probes as ultrafiltrate for 4 (n = 4) or 14 days (n = 2). The rate of ultrafiltrate collection was calculated every 12 h. Biochemical analyses were performed on ultrafiltrate collected on night 1 (12-24 h post-implantation) and night 4 (84-96 h post-implantation). Sections surrounding the probe and control tissue from the contralateral limb were harvested, stained with H&E and Masson's trichrome and scored based on the tissue response to the probe. Ultrafiltration probes were placed in the lamellar tissue in all six horses. Ultrafiltrate was collected from these probes at 55 (30-63) μL/h (median [interquartile range]). Fluid production decreased significantly with time from night 3 onwards (P < 0.05). There was no significant change in the constituents of the ultrafiltrate between nights 1 and 4 (P > 0.05). The technique was well tolerated. This study demonstrates that ultrafiltration can be used to sample equine digital lamellar interstitial fluid, and has potential for measuring lamellar drug levels.

Fibre digestibility, abundance of faecal bacteria and plasma acetate concentrations in overweight adult mares

The purpose of the present study was to compare digestibility of grass hay, faecal and plasma volatile fatty acid (VFA) concentrations, and faecal bacterial abundance in overweight and moderate-condition mares. Five overweight adult mixed-breed mares and five adult mixed-breed mares in moderate condition were housed individually and limit-fed orchard grass (Dactylis glomerata) hay at 20 g/kg body weight (as fed) daily for 14 d. Forage DM and fibre digestibility were determined using AOAC methods; digestible energy was measured using bomb calorimetry; plasma and faecal VFA concentrations were determined by use of GC and MS; faecal Firmicutes, Bacteroidetes, Fibrobacter succinogenes, Ruminococcus flavefaciens and total bacteria abundance was determined by quantitative real-time PCR using previously designed phylum-specific 16S ribosomal RNA gene primers. No differences in hay digestibility, faecal VFA concentrations or faecal bacterial abundance were detected between overweight and moderate-condition mares. Mean plasma acetate concentrations were higher (P = 0·03) in overweight (1·55 (range 1·43-1·65) mmol/l) v. moderate-condition (1·39 (range 1·22-1·47) mmol/l) mares. We conclude that the higher plasma acetate in overweight mares should be further investigated as a potential link between gut microbes and obesity in horses.

Continuous digital hypothermia initiated after the onset of lameness prevents lamellar failure in the oligofructose laminitis model

REASONS FOR PERFORMING STUDY

Prophylactic digital hypothermia reduces the severity of acute laminitis experimentally but there is no evidence for its efficacy as a treatment once lameness has already developed.

OBJECTIVES

To investigate the therapeutic effects of digital hypothermia, applied after the onset of lameness, in an experimental acute laminitis model.

STUDY DESIGN

Randomised, controlled (within subject), blinded, experimental trial.

METHODS

Eight Standardbred horses underwent laminitis induction using the oligofructose model. Once lameness was detected at the walk, one forelimb was continuously cooled (CRYO), with the other forelimb maintained at ambient temperature (NON-RX). Dorsal lamellar sections (proximal, middle and distal) harvested 36 h after the onset of lameness/initiation of cryotherapy were analysed by 2 blinded observers: laminitis pathology was scored (0 [normal] to 4 [severe]) and morphometric analyses performed.

RESULTS

Median (interquartile range) histological scores were greater (P<0.05) in NON-RX (proximal 2.8 [2.5-4]; middle 3.5 [2-4]; distal 2.5 [2-3.8]) compared with CRYO limbs (proximal 0.5 [0.5-1.4]; middle 1 [0.6-1]; distal 0.75 [0.5-1]). There was complete physical separation of lamellar dermis from epidermis (score of 4) in 4 of the NON-RX feet at one or more section level(s), which was not observed in any CRYO sections. Histomorphometry was thus limited to sections that remained intact; there was a trend of increased total (TELL) and secondary (SELL) epidermal lamellar length and decreased secondary epidermal lamellar width (SELW) in NON-RX limbs compared with CRYO at all 3 levels; differences were significant (P<0.05) for SELL and SELW in the distal sections.

CONCLUSIONS

Digital hypothermia reduced the severity of lamellar injury and prevented lamellar structural failure (complete dermoepidermal separation) when initiated at the detection of lameness in an acute laminitis model. This study provides the first evidence to support the use of therapeutic digital hypothermia as a treatment for acute laminitis.

An in vitro model of the horse gut microbiome enables identification of lactate-utilizing bacteria that differentially respond to starch induction

Laminitis is a chronic, crippling disease triggered by the sudden influx of dietary starch. Starch reaches the hindgut resulting in enrichment of lactic acid bacteria, lactate accumulation, and acidification of the gut contents. Bacterial products enter the bloodstream and precipitate systemic inflammation. Hindgut lactate levels are normally low because specific bacterial groups convert lactate to short chain fatty acids. Why this mechanism fails when lactate levels rapidly rise, and why some hindgut communities can recover is unknown. Fecal samples from three adult horses eating identical diets provided bacterial communities for this in vitro study. Triplicate microcosms of fecal slurries were enriched with lactate and/or starch. Metabolic products (short chain fatty acids, headspace gases, and hydrogen sulfide) were measured and microbial community compositions determined using Illumina 16S rRNA sequencing over 12-hour intervals. We report that patterns of change in short chain fatty acid levels and pH in our in vitro system are similar to those seen in in vivo laminitis induction models. Community differences between microcosms with disparate abilities to clear excess lactate suggest profiles conferring resistance of starch-induction conditions. Where lactate levels recover following starch induction conditions, propionate and acetate levels rise correspondingly and taxa related to Megasphaeraelsdenii reach levels exceeding 70% relative abundance. In lactate and control cultures, taxa related to Veillonellamontpellierensis are enriched as lactate levels fall. Understanding these community differences and factors promoting the growth of specific lactate utilizing taxa may be useful to prevent acidosis under starch-induction conditions.